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although the entertainment industry is constantly releasing a new hollywood blockbuster , tv series , video game , graphic novel , or comic book about batman ’ s latest adventures , it is important to understand that the extraordinary image of a human being with bat features and qualities existed long ago in the americas . this is one of the key messages from this unique pendant from ancient panama . archaeologists found this pendant with the remains of a male elder in a grave at the cemetery called sitio conte , located west of panama city in the province of coclé and approximately twenty-five miles from the pacific ocean . the sitio conte cemetery was one of several major regional cemeteries in the first millennium c.e . currently , archaeologists are excavating el caño , another major cemetery very close to sitio conte with similar types of graves and art objects . at least 200 people , mostly adult men , were buried at the sitio conte cemetery between 750 and 950 c.e . besides this pendant , the male elder 's grave was filled with pottery and tools as well as many types of jewelry and ornaments in various materials , including metals , animal bone , and stone . the bat-human pendant was found near two other pendants that look completely different—one displays two male warriors ( below ) and the other one mixes bat and crocodile imagery . aside from this older man and his items , fourteen men of various ages were interred alongside him in the grave and most of them also had some pottery , tools , jewelry , or ornaments . materials and function the bat-human pendant is in very good condition overall . one loss can be observed at the right bottom corner and another one can be seen at the left top corner . it is made with a gold-copper alloy ( typical of ancient central american metalwork ) , and showcases the artists ’ skills with a variety of materials and techniques . it was fabricated using the lost-wax method , which requires many steps before the pendant is cast by pouring liquid metal into a mold . in addition to casting , the curved wings with pointed extensions were made from sheets hammered into shape and attached to the body at the shoulders . along with casting and hammering , the artists also inlaid materials into the four round and now empty depressions . the inlays have not survived after being buried for centuries in water-logged soil ( the cemetery was located along the great coclé river ) . however , archaeologists have observed traces of resin in the large central depression , indicating that some sort of stone was held in place through this method . the other three depressions were inlaid differently , which is indicated by pairs of holes in the metal back . such holes would have had a cord pass through the back , holding the stone in place . it is likely that the smaller depressions would have once held pyrite or emeralds . emeralds were a highly valued material and were used across mesoamerica and central america . in fact , a pendant in another sitio conte grave has a large square emerald in its back and , as such , bears witness from ancient panama to the value of greenstone across mesoamerica and central america . on the back of the pendant are two suspension rings , which confirm that this object was designed to be hung on a cord around the neck , either alone , or , more likely , with other pendants such as those found in the grave . there is evidence dating from the time of spanish conquest in the 16th century that people living on the caribbean coast of panama wore mirrors suspended from their necks . iconography in addition to the mixture of techniques and materials , this pendant ’ s imagery also is a blend : human being and bat . today there are more than one hundred known bat species in panama . several features of the pendant resemble bats such as its large ears , interlocking canines , and partially folded wings with pointed contours . the triangular or leaf-like nose panel resembles that of the leaf-nosed bats ( family phyllostomidae ) . bats—especially with the wings spread open—are a popular subject for sitio conte pottery and pendants . however , this figure stands straight on two legs with two arms and hands raised like that of a human . all of its fingers are separated from the wings—unlike actual bats whose free thumb and fingers are encased in its wings . the figure has a trapezoidal forehead contour and upper and lower sets of square teeth behind canines . these features resemble human-shaped pottery vessels found in sitio conte graves . the figure is dressed in a loincloth , which is articulated by contour lines that run across the knees and a triangular cloth tucked between the legs . the bat-human figure also wears an elaborate head ornament in the shape of a trapezoidal panel . symbolism it is not hard to understand why humans create images of themselves possessing the bat ’ s striking physical features and impressive abilities , such as adroit flight and locating prey at night . bat-human imagery in ancient central american art is often linked to religious beliefs and practices . there is evidence of ritual specialists in ancient central american societies : men and women who go through rigorous training about the natural and supernatural worlds to gain knowledge that helped them accomplish a goal for the community . the specialists may have animal assistants and they may also transform into these assistants during rituals to acquire the animal ’ s features and abilities . beliefs and practices of ritual specialists may also help us understand the pyrite originally in the central depression ( and possibly the three smaller ones : ) ritual specialists used mirrors like doorways opening into the supernatural realm . mirrors let them see parts of the universe invisible to the ordinary eye . together , these observations may even lead to the hypothesis that the man buried with it served as a ritual specialist in his community in central panama . unfortunately , there is no way to confirm his identity or role in his society . that said , other tools in his immediate vicinity in the grave can be linked to ritual : he had two pyrite mirrors ( only their stone backs survive today ) and a pair of painted ceramic incense burners . whatever the man ’ s exact identity in his community , today we can see very clearly a man outfitted for his afterlife with many powerful ornaments , tools , and images . essay by dr. karen o ’ day river of gold : precolumbian treasures from sitio conte , university of pennsylvania museum of archaeology and anthropology ( penn museum ) additional resources : the mirror pendant in the form of a bat-human at the peabody museum of archaeology and ethnology , harvard university warwick bray , sitio conte metalwork in its pan-american context , '' in river of gold : pre-columbian treasures from sitio conte* , edited by pamela hearne and robert j. sharer ( the university museum , university of pennsylvania , philadelphia , 1992 ) , pp . 32-46 . megan gambino , the call of the panama bats , smithsonian magazine , 2009 pamela hearne and robert j. sharer , river of gold : treasures from sitio conte ( the university museum university of pennsylvania , philadelphia , 1992 ) . john w. hoopes , and oscar m. fonseca z. , `` goldwork and chibchan identity : endogenous change and diffuse unity in the isthmo-colombian area , '' in gold and power in ancient costa rica , panama , and colombia , edited by jeffrey quilter & amp ; john w. hoopes ( dumbarton oaks research library and collection , washington , dc. , 2003 ) , pp . 49-89 . john kricher , a neotropical companion , an introduction to the animals , plants , & amp ; ecosystems of the new world tropics ( princeton university press , princeton , new jersey , 1997 ) . olga linares , `` ecology and the arts in ancient panama : on the development of social rank and symbolism in the central provinces , '' studies in pre-columbian art and archaeology , number seventeen ( dumbarton oaks research library and collection , washington , dc. , 1977 ) . samuel k. lothrop , coclé : an archaeological study of central panama , part i. memoirs of the peabody museum of archaeology and ethnology , harvard university vol . vii . ( peabody museum , cambridge , massachusetts ) . julia mayo and carlos mayo , `` el descubrimiento de un cementerio de élite en el caño : indicios de un patrón funerario en el valle de río grande , coclé , panamá , '' arqueología iberoamericana vol 20 , 2013 , pp . 3-27 . laura navarro and joaquín arroyo-cabrales , `` bats in ancient mesoamerica , '' in the archaeology of mesoamerican animals , edited by christopher m. getz and kitty f. emery , ( lockwood press , atlanta , georgia ) , pp . 583-605 . karen o ’ day , `` the sitio conte cemetery in ancient panama : where lord 15 wore his ornaments in 'great quantity , ' '' in wearing culture : dress and regalia in early mesoamerica and central america , edited by heather orr and matthew g. looper ( university press of colorado , boulder 2014 ) , pp . 1-28 . nicholas j. saunders , “ 'catching the light ' : technologies of power and enchantment in pre-columbian goldworking , '' in gold and power in ancient costa rica , panama , and colombia , edited by jeffrey quilter & amp ; john w. hoopes ( dumbarton oaks research library and collection , washington , dc . 2003 ) , pp . 15-47 . rebecca stone , the jaguar within : shamanic trance in ancient central and south american art ( university of texas press , austin , 2011 ) rebecca stone-miller , seeing with new eyes : highlights of the michael c. carlos museum collection of art of the ancient americas ( michael c. carlos museum , atlanta , georgia ) . a.r . williams , `` the golden chiefs of panama , '' national geographic 221 ( 1 ) , pp . 66-81 .
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although the entertainment industry is constantly releasing a new hollywood blockbuster , tv series , video game , graphic novel , or comic book about batman ’ s latest adventures , it is important to understand that the extraordinary image of a human being with bat features and qualities existed long ago in the americas . this is one of the key messages from this unique pendant from ancient panama .
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is this institutional tomb robbery consider science ?
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buddhism in china buddhism probably arrived in china during the han dynasty ( 206 b.c.e . - 220 c.e . ) , and became a central feature of chinese culture during the period of division that followed . buddhist teaching ascribed great merit to the reproduction of images of buddhas and bodhisattvas , in which the artisans had to follow strict rules of iconography . a twelfth-century catalogue of the chinese imperial painting collection lists daoist and buddhist works from the time of gu kaizhi ( c. 344-406 c.e . ) onwards . however , no paintings by major artists of this period have survived , because foreign religions were proscribed between 842 and 845 , and many buddhist monuments and works of art were destroyed . the valley of the thousand buddhas what has survived from the tang period ( 618-906 ) is an important collection of buddhist paintings on silk and paper , found in cave 17 , in the valley of the thousand buddhas at the chinese end of the silk road . since dunhuang was under tibetan occupation at this time , its cave shrines and paintings escaped destruction . the `` caves of the thousand buddhas , '' or qianfodong , are situated at mogao , about 25 kilometres south-east of the oasis town of dunhuang in gansu province , western china , in the middle of the desert . by the late fourth century , the area had become a busy desert crossroads on the caravan routes of the silk road linking china and the west . traders , pilgrims and other travelers stopped at the oasis town to stock up with provisions , pray for the journey ahead or give thanks for their survival . at about this time wandering monks carved the first caves into the long cliff stretching almost 2 kilometers in length along the daquan river . over the next millennium more than 1000 caves of varying sizes were dug . around five hundred of these were decorated as cave temples , carved from the gravel conglomerate of the escarpment . this material was not suitable for sculpture , as at other famous buddhist cave temples at yungang and longmen . the caves of the thousand buddhas gained their name from the legend of a monk who dreamt he saw a cloud with a thousand buddhas floating over the valley . sealed for a thousand years , then rediscovered when the silk road was abandoned under the ming dynasty ( 1368-1644 ) , oasis towns lost their importance and many were deserted . although the mogao caves were not completely abandoned , by the nineteenth century they were largely forgotten , with only a few monks staying at the site . unknown to them , at some point in the early eleventh century , an incredible archive—with up to 50,000 documents , hundreds of paintings , together with textiles and other artifacts—was sealed up in one of the caves ( cave 17 ) . its entrance concealed behind a wall painting , the cave remained hidden from sight for centuries , until 1900 , when it was discovered by wang yuanlu , a daoist monk who had appointed himself abbot and guardian of the caves . the first western expedition to reach dunhuang , led by a hungarian count , arrived in 1879 . more than twenty years later one of its members , lajos lóczy , drew the attention of the hungarian-born marc aurel stein , by then a well-known british archaeologist and explorer , to the importance of the caves . stein reached dunhuang and mogao in 1907 during his second expedition to central asia . by this time , he had heard rumors of the walled-in cave and its contents . after delicate negotiations with wang yuanlu , stein negotiated access to the cave . `` heaped up in layers , '' stein wrote , `` but without any order , there appeared in the dim light of the priest 's little lamp a solid mass of manuscript bundles rising to a height of nearly ten feet ... . not in the driest soil could relics of a ruined site have so completely escaped injury as they had here in a carefully selected rock chamber , where , hidden behind a brick wall , ... . these masses of manuscripts had lain undisturbed for centuries . '' ( m. aurel stein , ruins of desert cathay ( 1912 ; reprint , new york , dover , 1987 ) . the abbot eventually sold stein seven thousand complete manuscripts and six thousand fragments , as well as several cases loaded with paintings , embroideries and other artifacts ; the money was used to fund restoration work at the caves.the manuscripts are now in the british library and the paintings have been divided between the national museum in new delhi and the british museum , where over three hundred paintings on silk , hemp and paper are kept . this painting is inscribed with the characters yinlu pu or `` bodhisattva leading the way . '' it is one of several examples from mogao of a bodhisattva leading the beautifully clad donor figure to the pure land , or paradise , indicated by a chinese building floating on clouds in the top left corner . the two figures are also supported by a cloud indicating that they are flying . the bodhisattva , shown much larger than the donor , is holding a censer and a banner in his hand . the banner is one of many of the same type found at mogao , with a triangular headpiece and streamers . the woman appears to be very wealthy , with gold hairpins in her hair . actual examples of these were found in chinese tombs . her fashionably plump figure suggests that the painting was executed in the ninth or tenth century . suggested readings : h. wang ( ed . ) , sir aurel stein . proceedings of the british museum study day 2002 ( london , british museum occasional paper 142 , 2004 ) . h. wang , money on the silk road . the evidence from eastern central asiato c. ad 800 ( london , british museum press , 2004 ) . s. whitfield , aurel stein on the silk road ( london , british museum press , 2004 ) . j. falconer , a. kelecsenyi , a. karteszi and l. russell-smith ( e. apor and h. wang eds . ) , catalogue of the collections of sir aurel stein in the library of the hungarian academy of sciences ( published jointly by the british museum and the library of the hungarian academy of sciences , budapest [ lhas oriental series 11 ] , 2002 ) . h. wang ( ed . ) , handbook to the stein collections in the uk ( london , british museum occasional paper 129 , 1999 ) . © trustees of the british museum
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buddhism in china buddhism probably arrived in china during the han dynasty ( 206 b.c.e . - 220 c.e .
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was there a religion native to china before buddhism ?
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buddhism in china buddhism probably arrived in china during the han dynasty ( 206 b.c.e . - 220 c.e . ) , and became a central feature of chinese culture during the period of division that followed . buddhist teaching ascribed great merit to the reproduction of images of buddhas and bodhisattvas , in which the artisans had to follow strict rules of iconography . a twelfth-century catalogue of the chinese imperial painting collection lists daoist and buddhist works from the time of gu kaizhi ( c. 344-406 c.e . ) onwards . however , no paintings by major artists of this period have survived , because foreign religions were proscribed between 842 and 845 , and many buddhist monuments and works of art were destroyed . the valley of the thousand buddhas what has survived from the tang period ( 618-906 ) is an important collection of buddhist paintings on silk and paper , found in cave 17 , in the valley of the thousand buddhas at the chinese end of the silk road . since dunhuang was under tibetan occupation at this time , its cave shrines and paintings escaped destruction . the `` caves of the thousand buddhas , '' or qianfodong , are situated at mogao , about 25 kilometres south-east of the oasis town of dunhuang in gansu province , western china , in the middle of the desert . by the late fourth century , the area had become a busy desert crossroads on the caravan routes of the silk road linking china and the west . traders , pilgrims and other travelers stopped at the oasis town to stock up with provisions , pray for the journey ahead or give thanks for their survival . at about this time wandering monks carved the first caves into the long cliff stretching almost 2 kilometers in length along the daquan river . over the next millennium more than 1000 caves of varying sizes were dug . around five hundred of these were decorated as cave temples , carved from the gravel conglomerate of the escarpment . this material was not suitable for sculpture , as at other famous buddhist cave temples at yungang and longmen . the caves of the thousand buddhas gained their name from the legend of a monk who dreamt he saw a cloud with a thousand buddhas floating over the valley . sealed for a thousand years , then rediscovered when the silk road was abandoned under the ming dynasty ( 1368-1644 ) , oasis towns lost their importance and many were deserted . although the mogao caves were not completely abandoned , by the nineteenth century they were largely forgotten , with only a few monks staying at the site . unknown to them , at some point in the early eleventh century , an incredible archive—with up to 50,000 documents , hundreds of paintings , together with textiles and other artifacts—was sealed up in one of the caves ( cave 17 ) . its entrance concealed behind a wall painting , the cave remained hidden from sight for centuries , until 1900 , when it was discovered by wang yuanlu , a daoist monk who had appointed himself abbot and guardian of the caves . the first western expedition to reach dunhuang , led by a hungarian count , arrived in 1879 . more than twenty years later one of its members , lajos lóczy , drew the attention of the hungarian-born marc aurel stein , by then a well-known british archaeologist and explorer , to the importance of the caves . stein reached dunhuang and mogao in 1907 during his second expedition to central asia . by this time , he had heard rumors of the walled-in cave and its contents . after delicate negotiations with wang yuanlu , stein negotiated access to the cave . `` heaped up in layers , '' stein wrote , `` but without any order , there appeared in the dim light of the priest 's little lamp a solid mass of manuscript bundles rising to a height of nearly ten feet ... . not in the driest soil could relics of a ruined site have so completely escaped injury as they had here in a carefully selected rock chamber , where , hidden behind a brick wall , ... . these masses of manuscripts had lain undisturbed for centuries . '' ( m. aurel stein , ruins of desert cathay ( 1912 ; reprint , new york , dover , 1987 ) . the abbot eventually sold stein seven thousand complete manuscripts and six thousand fragments , as well as several cases loaded with paintings , embroideries and other artifacts ; the money was used to fund restoration work at the caves.the manuscripts are now in the british library and the paintings have been divided between the national museum in new delhi and the british museum , where over three hundred paintings on silk , hemp and paper are kept . this painting is inscribed with the characters yinlu pu or `` bodhisattva leading the way . '' it is one of several examples from mogao of a bodhisattva leading the beautifully clad donor figure to the pure land , or paradise , indicated by a chinese building floating on clouds in the top left corner . the two figures are also supported by a cloud indicating that they are flying . the bodhisattva , shown much larger than the donor , is holding a censer and a banner in his hand . the banner is one of many of the same type found at mogao , with a triangular headpiece and streamers . the woman appears to be very wealthy , with gold hairpins in her hair . actual examples of these were found in chinese tombs . her fashionably plump figure suggests that the painting was executed in the ninth or tenth century . suggested readings : h. wang ( ed . ) , sir aurel stein . proceedings of the british museum study day 2002 ( london , british museum occasional paper 142 , 2004 ) . h. wang , money on the silk road . the evidence from eastern central asiato c. ad 800 ( london , british museum press , 2004 ) . s. whitfield , aurel stein on the silk road ( london , british museum press , 2004 ) . j. falconer , a. kelecsenyi , a. karteszi and l. russell-smith ( e. apor and h. wang eds . ) , catalogue of the collections of sir aurel stein in the library of the hungarian academy of sciences ( published jointly by the british museum and the library of the hungarian academy of sciences , budapest [ lhas oriental series 11 ] , 2002 ) . h. wang ( ed . ) , handbook to the stein collections in the uk ( london , british museum occasional paper 129 , 1999 ) . © trustees of the british museum
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proceedings of the british museum study day 2002 ( london , british museum occasional paper 142 , 2004 ) . h. wang , money on the silk road . the evidence from eastern central asiato c. ad 800 ( london , british museum press , 2004 ) .
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did buddism spread through the silk route ?
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buddhism in china buddhism probably arrived in china during the han dynasty ( 206 b.c.e . - 220 c.e . ) , and became a central feature of chinese culture during the period of division that followed . buddhist teaching ascribed great merit to the reproduction of images of buddhas and bodhisattvas , in which the artisans had to follow strict rules of iconography . a twelfth-century catalogue of the chinese imperial painting collection lists daoist and buddhist works from the time of gu kaizhi ( c. 344-406 c.e . ) onwards . however , no paintings by major artists of this period have survived , because foreign religions were proscribed between 842 and 845 , and many buddhist monuments and works of art were destroyed . the valley of the thousand buddhas what has survived from the tang period ( 618-906 ) is an important collection of buddhist paintings on silk and paper , found in cave 17 , in the valley of the thousand buddhas at the chinese end of the silk road . since dunhuang was under tibetan occupation at this time , its cave shrines and paintings escaped destruction . the `` caves of the thousand buddhas , '' or qianfodong , are situated at mogao , about 25 kilometres south-east of the oasis town of dunhuang in gansu province , western china , in the middle of the desert . by the late fourth century , the area had become a busy desert crossroads on the caravan routes of the silk road linking china and the west . traders , pilgrims and other travelers stopped at the oasis town to stock up with provisions , pray for the journey ahead or give thanks for their survival . at about this time wandering monks carved the first caves into the long cliff stretching almost 2 kilometers in length along the daquan river . over the next millennium more than 1000 caves of varying sizes were dug . around five hundred of these were decorated as cave temples , carved from the gravel conglomerate of the escarpment . this material was not suitable for sculpture , as at other famous buddhist cave temples at yungang and longmen . the caves of the thousand buddhas gained their name from the legend of a monk who dreamt he saw a cloud with a thousand buddhas floating over the valley . sealed for a thousand years , then rediscovered when the silk road was abandoned under the ming dynasty ( 1368-1644 ) , oasis towns lost their importance and many were deserted . although the mogao caves were not completely abandoned , by the nineteenth century they were largely forgotten , with only a few monks staying at the site . unknown to them , at some point in the early eleventh century , an incredible archive—with up to 50,000 documents , hundreds of paintings , together with textiles and other artifacts—was sealed up in one of the caves ( cave 17 ) . its entrance concealed behind a wall painting , the cave remained hidden from sight for centuries , until 1900 , when it was discovered by wang yuanlu , a daoist monk who had appointed himself abbot and guardian of the caves . the first western expedition to reach dunhuang , led by a hungarian count , arrived in 1879 . more than twenty years later one of its members , lajos lóczy , drew the attention of the hungarian-born marc aurel stein , by then a well-known british archaeologist and explorer , to the importance of the caves . stein reached dunhuang and mogao in 1907 during his second expedition to central asia . by this time , he had heard rumors of the walled-in cave and its contents . after delicate negotiations with wang yuanlu , stein negotiated access to the cave . `` heaped up in layers , '' stein wrote , `` but without any order , there appeared in the dim light of the priest 's little lamp a solid mass of manuscript bundles rising to a height of nearly ten feet ... . not in the driest soil could relics of a ruined site have so completely escaped injury as they had here in a carefully selected rock chamber , where , hidden behind a brick wall , ... . these masses of manuscripts had lain undisturbed for centuries . '' ( m. aurel stein , ruins of desert cathay ( 1912 ; reprint , new york , dover , 1987 ) . the abbot eventually sold stein seven thousand complete manuscripts and six thousand fragments , as well as several cases loaded with paintings , embroideries and other artifacts ; the money was used to fund restoration work at the caves.the manuscripts are now in the british library and the paintings have been divided between the national museum in new delhi and the british museum , where over three hundred paintings on silk , hemp and paper are kept . this painting is inscribed with the characters yinlu pu or `` bodhisattva leading the way . '' it is one of several examples from mogao of a bodhisattva leading the beautifully clad donor figure to the pure land , or paradise , indicated by a chinese building floating on clouds in the top left corner . the two figures are also supported by a cloud indicating that they are flying . the bodhisattva , shown much larger than the donor , is holding a censer and a banner in his hand . the banner is one of many of the same type found at mogao , with a triangular headpiece and streamers . the woman appears to be very wealthy , with gold hairpins in her hair . actual examples of these were found in chinese tombs . her fashionably plump figure suggests that the painting was executed in the ninth or tenth century . suggested readings : h. wang ( ed . ) , sir aurel stein . proceedings of the british museum study day 2002 ( london , british museum occasional paper 142 , 2004 ) . h. wang , money on the silk road . the evidence from eastern central asiato c. ad 800 ( london , british museum press , 2004 ) . s. whitfield , aurel stein on the silk road ( london , british museum press , 2004 ) . j. falconer , a. kelecsenyi , a. karteszi and l. russell-smith ( e. apor and h. wang eds . ) , catalogue of the collections of sir aurel stein in the library of the hungarian academy of sciences ( published jointly by the british museum and the library of the hungarian academy of sciences , budapest [ lhas oriental series 11 ] , 2002 ) . h. wang ( ed . ) , handbook to the stein collections in the uk ( london , british museum occasional paper 129 , 1999 ) . © trustees of the british museum
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buddhism in china buddhism probably arrived in china during the han dynasty ( 206 b.c.e . - 220 c.e .
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how and when did buddhism take over from confucianism ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society .
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whats the basic difference between an anthropologist and a paleontologist ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society .
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what does `` b.c.e '' stand for ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools .
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why do we have to always base things on assumption ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains .
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what prehistoric skills for communications existed and what those skills were ( as and when discovered ) that have been discovered which assisted in understanding and writing the prehistoric information of homosapiens ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world .
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what is the difference between anthropology and paleontology ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains .
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can someone help me explain the paradox of `` the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago '' , and `` archaeologists have discovered written records in egypt from 3200 bce , which is the accepted date at which history begins there '' ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ?
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how would you know that these are actually accurate and there might be more out there that 's more than you think there is like proving if mythology was real and not fake ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) .
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there are many years of history and i am very interested i wonder when did the world start ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains .
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the third bullet point at the top says that hieroglyphs in egypt were the oldest writing found , from 3200 bce , but was n't sumerian text created in 3000 bce ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ?
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can a group of symbols scratched on a rock representing something be considered writing ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit .
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in which language the historical documents available at egypt ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in .
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when explaining carbon dating what does bump off mean ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society .
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when you say that the neutron bumps off the proton ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools .
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maybe earlier societies used pictures to 'write ' things too ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident .
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in the eighth paragraph , how are the narratives surprisingly rich ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . ''
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how can u tell the age of a dinosaur bone that you randomly find in a layered ground platform like-landscape structure ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in .
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how do we know that carbon dating is accurate ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society .
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what if the hyroglyphs were a translation of a slang greek ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience .
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is the rise of domestication somehow connected to the rise of agriculture ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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why would people have so much intrest in the paloelithic life ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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what are some other ways archaeologists and historians might consider dividing the study of the past ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in .
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what is the difference between carbon dating and stratigraphic dating ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology .
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what is historians main tool ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) .
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how can be the skeleton in layer or in the land for very long time ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it .
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what are some examples of dead languages ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it .
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how do you determine if a language is a dead language ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society .
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why was scholars define prehistory ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ?
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what is the difference between prehistory and history ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) .
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what tools do archaeologists use ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in .
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is bce or bc earlier in time ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ?
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if historians are willing to acknowledge that the writings of civilizations or man could be biased or untrue , why use them as a `` credible '' source of information ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology .
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has there been any evidence that languages written in stone may have been destroyed by a conquering tribes or armies ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there .
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how would we be able to determine that man destroyed the hieroglyphs and that it was n't the simple decay of time that wiped out these early records of recorded history ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in .
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do the archeologist do more than one carbon dating measurements ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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what happens when historisns find new information that contradicts information thay have found previously , how do they know which information to trust ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques .
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can you tell me more about the tools mentioned in written records that archaeologists use to excavate ancient structures and burial sites ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology .
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i am confused written was invented in egypt or mesopotamia ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques .
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in the first paragraph , why is the human species now listed as homo sapiens sapiens ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today .
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what evidence have we recently found to say our modern human species has changed ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society .
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so was it the sumerian civilization that began writting or was the egyptians ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ?
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also do hieroglyphs count as history or pre-history ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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what are some other ways archaeologists and historians might consider dividing the study of the past ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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if historians consider mythology and lore that correlates between regions but that are n't introduced at the same time frame is it common for them to use it to see when the culture and people traveled ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records !
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is someone working on sharing/teaching a common world view ?
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overview scholars define prehistory as events that occurred before the existence of written records in a given culture or society . history refers to the time period after the invention of written records in a given culture or society . archaeologists have discovered written records in egypt from as early as 3200 bce , which is the accepted date at which history `` begins '' there . written records give historians resources to deal with that are more detailed in some ways than other records , such as archaeological or biological remains . the scope of history historians currently think that anatomically modern humans—our subspecies of homosapiens sapiens—have been around for roughly 200,000 of the planet ’ s 4.5 billion years . and even though 200,000 years is less that one 20,000th of the history of the planet , it is still a very long time ! for context , 200,000 years would represent at least 6,000 generations of your ancestors ( your grandparents are only 2 generations from you ) . 200,000 years is also nearly 1,000 times as long as the united states has been a country . it is 100 times as distant in the past as the time of jesus and the roman empire . it 's also 40 times as distant in the past as the earliest written records we have found . think about the scope of what must have happened during that time : adventures , sorrows , environmental change , and the rise and fall of civilizations . as historians , we have the privilege of exploring this vast expanse of human experience . written records our main tool as historians is what has been written by those who came before us . in fact , this is what formally defines history and sometimes sets it apart from archaeology and anthropology . for example , the oldest written records archaeologists have discovered in egypt are from over 5,000 years ago ; the date when they were created is the currently accepted date at which formal history ( as opposed to `` prehistory '' ) begins in that part of the world . of course , we might one day find older records ! even with written records , though , we have to be careful and thoughtful . the writing may be in a dead language that we know little about . if one tribe conquers another , we might only get the biased , one-sided story of those who won and wrote about it . many times , narratives are only written down after generations of being transmitted orally , through speech , with every transmitter of the story consciously or unconsciously changing the specifics . even for events that happened yesterday , two direct observers could have two completely different perceptions of what happened , how , and why . you can imagine that things get even tougher for prehistory , or the events that occurred before the existence of written records . but we still have many tools . archaeologists can excavate ancient structures and burial sites and begin to infer how the people lived from fossils ( like human remains ) and artifacts ( human-made items ) . archaeologists can estimate the age of fossils and artifacts through several techniques . carbon dating measures the amount of radioactive carbon in fossils to place them in time . age can also be determined by identifying the age of the layer of rock that the artifacts are buried in . this is called stratigraphic dating , from the latin word_stratum_ , meaning `` layer . '' linguists can often piece together possible human migrations and connections based on similarities in modern , living languages . similarly , geneticists can piece together how humanity may have spread and intermingled based on genetic similarities and differences in populations today . $ ^1 $ uncertainty remains by putting all of these pieces together , we can construct surprisingly rich narratives of the distant past . but we should never let the tools and knowledge we have make us overconfident . after all , every piece of historical evidence needs to be closely read , sourced , interpreted , contextualized , and compared with other available sources . these kinds of thinking and questioning are the historians ' toolkit . even today , we can only piece together a tiny fragment of all that has occurred . and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ? should prehistory and history be divided as they currently are—prehistory meaning before writing , and history meaning after writing ? what are some other ways archaeologists and historians might consider dividing the study of the past ? how much information—artifacts , fossils , or other evidence—do you think needs to be present in order for something to be “ knowable ” ?
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and a lot of that understanding could very well be wrong because it is inevitably partial and incomplete . many things that historians take as a given today will be questioned by future historians armed with new tools and new evidence . what do you think ?
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in the conclusion , is there an example of a future tool that historians are developing to better tell the stories of prehistory ?
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key points mixtures with uniform composition are called homogeneous mixtures or solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . introduction : mixtures and solutions in real life , we often encounter substances that are mixtures of different elements and compounds . one example of a mixture is the human body . did you know that the human body is approximately $ 57\ % $ water by mass ? we are basically an assortment of biological molecules , gases , and inorganic ions dissolved in water . i do n't know about you , but i find that pretty mind-boggling ! if substances are mixed together in such a way that the composition is the same throughout the sample , they are called homogeneous mixtures . in contrast , a mixture that does not have a uniform composition throughout the sample is called heterogeneous . homogeneous mixtures are also known as solutions , and solutions can contain components that are solids , liquids and/or gases . we often want to be able to quantify the amount of a species that is in the solution , which is called the concentration of that species . in this article , we 'll look at how to describe solutions quantitatively , and discuss how that information can be used when doing stoichiometric calculations . molar concentration the component of a solution that is present in the largest amount is known as the solvent . any chemical species mixed in the solvent is called a solute , and solutes can be gases , liquids , or solids . for example , earth 's atmosphere is a mixture of $ 78\ % $ nitrogen gas , $ 21\ % $ oxygen gas , and $ 1\ % $ argon , carbon dioxide , and other gases . we can think of the atmosphere as a solution where nitrogen gas is the solvent , and the solutes are oxygen , argon and carbon dioxide . the molarity or molar concentration of a solute is defined as the number of moles of solute per liter of solution ( not per liter of solvent ! ) : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molarity has units of $ \dfrac { \text { mol } } { \text { liter } } $ , which can be abbreviated as molar or $ \text m $ ( pronounced `` molar '' ) . the molar concentration of the solute is sometimes abbreviated by putting square brackets around the chemical formula of the solute . for example , the concentration of chloride ions in a solution can be written as $ [ \text { cl } ^- ] $ . molar concentration allows us to convert between the volume of the solution and the moles ( or mass ) of the solute . concept check : bronze is an alloy that can be thought of as a solid solution of ~ $ 88\ % $ copper mixed with $ 12\ % $ tin . what is the solute and solvent in bronze ? example 1 : calculating the molar concentration of a solute let 's consider a solution made by dissolving $ 2.355\ , \text g $ of sulfuric acid , $ \text h_2 \text { so } _4 $ , in water . the total volume of the solution is $ 50.0\ , \text { ml } $ . what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ? to find $ [ \text h_2 \text { so } _4 ] $ we need to find out how many moles of sulfuric acid are in solution . we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ? example 2 : making a solution with a specific concentration sometimes we have a desired concentration and volume of solution , and we want to know how much solute we need to make the solution . in that case , we can rearrange the molarity equation to solve for the moles of solute . $ \text { mol solute } = { \text { molarity } } \times { \text { l of solution } } $ for example , let 's say we want to make $ 0.250\ , \text { l } $ of an aqueous solution with $ [ \text { nacl } ] =0.800\ , \text { m } $ . what mass of the solute , $ \text { nacl } $ , would we need to make this solution ? we can use the rearranged molarity equation to calculate the moles of $ \text { nacl } $ needed for the specified concentration and volume : $ \begin { align } \text { mol nacl } & amp ; = [ \text { nacl } ] \times { \text { l of solution } } \ & amp ; =0.800\ , \dfrac { \text { mol } } { \cancel { \text l } } \times 0.250\ , \cancel { \text { l } } \ & amp ; =0.200\ , \text { mol nacl } \end { align } $ we can then use the molecular weight of sodium chloride , $ 58.44\ , \dfrac { \text g } { \text { mol } } $ , to convert from moles to grams of $ \text { nacl } $ : $ \text { mass of nacl } =0.200\ , \cancel { \text { mol } } \times \dfrac { 58.44\ , \text g } { 1\ , \cancel { \text { mol } } } = 11.7\ , \text { g nacl } $ in practice , we could use this information to make our solution as follows : step $ 1.~ $ weigh out $ 11.7\ , \text g $ of sodium chloride . step $ 2.~ $ transfer the sodium chloride to a clean , dry flask . step $ 3.~ $ add water to the $ \text { nacl } $ until the total volume of the solution is $ 250\ , \text { ml } $ . step $ 4.~ $ stir until the $ \text { nacl } $ is completely dissolved . the accuracy of our molar concentration depends on our choice of glassware , as well as the accuracy of the balance we use to measure out the solute . the glassware determines the accuracy of our solution volume . if we are n't being too picky , we might mix the solution in a erlenmeyer flask or beaker . if we want to extremely precise , such as when making a standard solution for an analytical chemistry experiment , we would probably mix the solute and solvent in a volumetric flask ( see picture below ) . summary mixtures with uniform composition are called homogeneous solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . try it : the stoichiometry of a precipitation reaction molarity is a useful concept for stoichiometric calculations involving reactions in solution , such precipitation and neutralization reactions . for example , consider the precipitation reaction that occurs between $ \text { pb ( no } _3 ) _2 ( aq ) $ and $ \text { ki } ( aq ) $ . when these two solutions are combined , bright yellow $ \text { pbi } _2 ( s ) $ precipitates out of solution . the balanced equation for this reaction is : $ \text { pb ( no } _3 ) _2 ( aq ) + 2\text { ki } ( aq ) \rightarrow \text { pbi } _2 ( s ) + 2\text { kno } _3 ( aq ) $ if we have $ 0.1\ , \text { l } $ of $ 0.10\ , \text { m pb ( no } _3 ) _2 $ , what volume of $ 0.10\ , \text { m ki } ( aq ) $ should we add to react with all the $ \text { pb ( no } _3 ) _2 ( aq ) $ ?
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example 2 : making a solution with a specific concentration sometimes we have a desired concentration and volume of solution , and we want to know how much solute we need to make the solution . in that case , we can rearrange the molarity equation to solve for the moles of solute . $ \text { mol solute } = { \text { molarity } } \times { \text { l of solution } } $ for example , let 's say we want to make $ 0.250\ , \text { l } $ of an aqueous solution with $ [ \text { nacl } ] =0.800\ , \text { m } $ .
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i was told in school that molarity should be moles/dm^3 , but is this different from moles/litres ?
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key points mixtures with uniform composition are called homogeneous mixtures or solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . introduction : mixtures and solutions in real life , we often encounter substances that are mixtures of different elements and compounds . one example of a mixture is the human body . did you know that the human body is approximately $ 57\ % $ water by mass ? we are basically an assortment of biological molecules , gases , and inorganic ions dissolved in water . i do n't know about you , but i find that pretty mind-boggling ! if substances are mixed together in such a way that the composition is the same throughout the sample , they are called homogeneous mixtures . in contrast , a mixture that does not have a uniform composition throughout the sample is called heterogeneous . homogeneous mixtures are also known as solutions , and solutions can contain components that are solids , liquids and/or gases . we often want to be able to quantify the amount of a species that is in the solution , which is called the concentration of that species . in this article , we 'll look at how to describe solutions quantitatively , and discuss how that information can be used when doing stoichiometric calculations . molar concentration the component of a solution that is present in the largest amount is known as the solvent . any chemical species mixed in the solvent is called a solute , and solutes can be gases , liquids , or solids . for example , earth 's atmosphere is a mixture of $ 78\ % $ nitrogen gas , $ 21\ % $ oxygen gas , and $ 1\ % $ argon , carbon dioxide , and other gases . we can think of the atmosphere as a solution where nitrogen gas is the solvent , and the solutes are oxygen , argon and carbon dioxide . the molarity or molar concentration of a solute is defined as the number of moles of solute per liter of solution ( not per liter of solvent ! ) : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molarity has units of $ \dfrac { \text { mol } } { \text { liter } } $ , which can be abbreviated as molar or $ \text m $ ( pronounced `` molar '' ) . the molar concentration of the solute is sometimes abbreviated by putting square brackets around the chemical formula of the solute . for example , the concentration of chloride ions in a solution can be written as $ [ \text { cl } ^- ] $ . molar concentration allows us to convert between the volume of the solution and the moles ( or mass ) of the solute . concept check : bronze is an alloy that can be thought of as a solid solution of ~ $ 88\ % $ copper mixed with $ 12\ % $ tin . what is the solute and solvent in bronze ? example 1 : calculating the molar concentration of a solute let 's consider a solution made by dissolving $ 2.355\ , \text g $ of sulfuric acid , $ \text h_2 \text { so } _4 $ , in water . the total volume of the solution is $ 50.0\ , \text { ml } $ . what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ? to find $ [ \text h_2 \text { so } _4 ] $ we need to find out how many moles of sulfuric acid are in solution . we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ? example 2 : making a solution with a specific concentration sometimes we have a desired concentration and volume of solution , and we want to know how much solute we need to make the solution . in that case , we can rearrange the molarity equation to solve for the moles of solute . $ \text { mol solute } = { \text { molarity } } \times { \text { l of solution } } $ for example , let 's say we want to make $ 0.250\ , \text { l } $ of an aqueous solution with $ [ \text { nacl } ] =0.800\ , \text { m } $ . what mass of the solute , $ \text { nacl } $ , would we need to make this solution ? we can use the rearranged molarity equation to calculate the moles of $ \text { nacl } $ needed for the specified concentration and volume : $ \begin { align } \text { mol nacl } & amp ; = [ \text { nacl } ] \times { \text { l of solution } } \ & amp ; =0.800\ , \dfrac { \text { mol } } { \cancel { \text l } } \times 0.250\ , \cancel { \text { l } } \ & amp ; =0.200\ , \text { mol nacl } \end { align } $ we can then use the molecular weight of sodium chloride , $ 58.44\ , \dfrac { \text g } { \text { mol } } $ , to convert from moles to grams of $ \text { nacl } $ : $ \text { mass of nacl } =0.200\ , \cancel { \text { mol } } \times \dfrac { 58.44\ , \text g } { 1\ , \cancel { \text { mol } } } = 11.7\ , \text { g nacl } $ in practice , we could use this information to make our solution as follows : step $ 1.~ $ weigh out $ 11.7\ , \text g $ of sodium chloride . step $ 2.~ $ transfer the sodium chloride to a clean , dry flask . step $ 3.~ $ add water to the $ \text { nacl } $ until the total volume of the solution is $ 250\ , \text { ml } $ . step $ 4.~ $ stir until the $ \text { nacl } $ is completely dissolved . the accuracy of our molar concentration depends on our choice of glassware , as well as the accuracy of the balance we use to measure out the solute . the glassware determines the accuracy of our solution volume . if we are n't being too picky , we might mix the solution in a erlenmeyer flask or beaker . if we want to extremely precise , such as when making a standard solution for an analytical chemistry experiment , we would probably mix the solute and solvent in a volumetric flask ( see picture below ) . summary mixtures with uniform composition are called homogeneous solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . try it : the stoichiometry of a precipitation reaction molarity is a useful concept for stoichiometric calculations involving reactions in solution , such precipitation and neutralization reactions . for example , consider the precipitation reaction that occurs between $ \text { pb ( no } _3 ) _2 ( aq ) $ and $ \text { ki } ( aq ) $ . when these two solutions are combined , bright yellow $ \text { pbi } _2 ( s ) $ precipitates out of solution . the balanced equation for this reaction is : $ \text { pb ( no } _3 ) _2 ( aq ) + 2\text { ki } ( aq ) \rightarrow \text { pbi } _2 ( s ) + 2\text { kno } _3 ( aq ) $ if we have $ 0.1\ , \text { l } $ of $ 0.10\ , \text { m pb ( no } _3 ) _2 $ , what volume of $ 0.10\ , \text { m ki } ( aq ) $ should we add to react with all the $ \text { pb ( no } _3 ) _2 ( aq ) $ ?
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the molarity or molar concentration of a solute is defined as the number of moles of solute per liter of solution ( not per liter of solvent ! ) : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molarity has units of $ \dfrac { \text { mol } } { \text { liter } } $ , which can be abbreviated as molar or $ \text m $ ( pronounced `` molar '' ) . the molar concentration of the solute is sometimes abbreviated by putting square brackets around the chemical formula of the solute .
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in the question that says : is molarity the same thing as molality ?
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key points mixtures with uniform composition are called homogeneous mixtures or solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . introduction : mixtures and solutions in real life , we often encounter substances that are mixtures of different elements and compounds . one example of a mixture is the human body . did you know that the human body is approximately $ 57\ % $ water by mass ? we are basically an assortment of biological molecules , gases , and inorganic ions dissolved in water . i do n't know about you , but i find that pretty mind-boggling ! if substances are mixed together in such a way that the composition is the same throughout the sample , they are called homogeneous mixtures . in contrast , a mixture that does not have a uniform composition throughout the sample is called heterogeneous . homogeneous mixtures are also known as solutions , and solutions can contain components that are solids , liquids and/or gases . we often want to be able to quantify the amount of a species that is in the solution , which is called the concentration of that species . in this article , we 'll look at how to describe solutions quantitatively , and discuss how that information can be used when doing stoichiometric calculations . molar concentration the component of a solution that is present in the largest amount is known as the solvent . any chemical species mixed in the solvent is called a solute , and solutes can be gases , liquids , or solids . for example , earth 's atmosphere is a mixture of $ 78\ % $ nitrogen gas , $ 21\ % $ oxygen gas , and $ 1\ % $ argon , carbon dioxide , and other gases . we can think of the atmosphere as a solution where nitrogen gas is the solvent , and the solutes are oxygen , argon and carbon dioxide . the molarity or molar concentration of a solute is defined as the number of moles of solute per liter of solution ( not per liter of solvent ! ) : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molarity has units of $ \dfrac { \text { mol } } { \text { liter } } $ , which can be abbreviated as molar or $ \text m $ ( pronounced `` molar '' ) . the molar concentration of the solute is sometimes abbreviated by putting square brackets around the chemical formula of the solute . for example , the concentration of chloride ions in a solution can be written as $ [ \text { cl } ^- ] $ . molar concentration allows us to convert between the volume of the solution and the moles ( or mass ) of the solute . concept check : bronze is an alloy that can be thought of as a solid solution of ~ $ 88\ % $ copper mixed with $ 12\ % $ tin . what is the solute and solvent in bronze ? example 1 : calculating the molar concentration of a solute let 's consider a solution made by dissolving $ 2.355\ , \text g $ of sulfuric acid , $ \text h_2 \text { so } _4 $ , in water . the total volume of the solution is $ 50.0\ , \text { ml } $ . what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ? to find $ [ \text h_2 \text { so } _4 ] $ we need to find out how many moles of sulfuric acid are in solution . we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ? example 2 : making a solution with a specific concentration sometimes we have a desired concentration and volume of solution , and we want to know how much solute we need to make the solution . in that case , we can rearrange the molarity equation to solve for the moles of solute . $ \text { mol solute } = { \text { molarity } } \times { \text { l of solution } } $ for example , let 's say we want to make $ 0.250\ , \text { l } $ of an aqueous solution with $ [ \text { nacl } ] =0.800\ , \text { m } $ . what mass of the solute , $ \text { nacl } $ , would we need to make this solution ? we can use the rearranged molarity equation to calculate the moles of $ \text { nacl } $ needed for the specified concentration and volume : $ \begin { align } \text { mol nacl } & amp ; = [ \text { nacl } ] \times { \text { l of solution } } \ & amp ; =0.800\ , \dfrac { \text { mol } } { \cancel { \text l } } \times 0.250\ , \cancel { \text { l } } \ & amp ; =0.200\ , \text { mol nacl } \end { align } $ we can then use the molecular weight of sodium chloride , $ 58.44\ , \dfrac { \text g } { \text { mol } } $ , to convert from moles to grams of $ \text { nacl } $ : $ \text { mass of nacl } =0.200\ , \cancel { \text { mol } } \times \dfrac { 58.44\ , \text g } { 1\ , \cancel { \text { mol } } } = 11.7\ , \text { g nacl } $ in practice , we could use this information to make our solution as follows : step $ 1.~ $ weigh out $ 11.7\ , \text g $ of sodium chloride . step $ 2.~ $ transfer the sodium chloride to a clean , dry flask . step $ 3.~ $ add water to the $ \text { nacl } $ until the total volume of the solution is $ 250\ , \text { ml } $ . step $ 4.~ $ stir until the $ \text { nacl } $ is completely dissolved . the accuracy of our molar concentration depends on our choice of glassware , as well as the accuracy of the balance we use to measure out the solute . the glassware determines the accuracy of our solution volume . if we are n't being too picky , we might mix the solution in a erlenmeyer flask or beaker . if we want to extremely precise , such as when making a standard solution for an analytical chemistry experiment , we would probably mix the solute and solvent in a volumetric flask ( see picture below ) . summary mixtures with uniform composition are called homogeneous solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . try it : the stoichiometry of a precipitation reaction molarity is a useful concept for stoichiometric calculations involving reactions in solution , such precipitation and neutralization reactions . for example , consider the precipitation reaction that occurs between $ \text { pb ( no } _3 ) _2 ( aq ) $ and $ \text { ki } ( aq ) $ . when these two solutions are combined , bright yellow $ \text { pbi } _2 ( s ) $ precipitates out of solution . the balanced equation for this reaction is : $ \text { pb ( no } _3 ) _2 ( aq ) + 2\text { ki } ( aq ) \rightarrow \text { pbi } _2 ( s ) + 2\text { kno } _3 ( aq ) $ if we have $ 0.1\ , \text { l } $ of $ 0.10\ , \text { m pb ( no } _3 ) _2 $ , what volume of $ 0.10\ , \text { m ki } ( aq ) $ should we add to react with all the $ \text { pb ( no } _3 ) _2 ( aq ) $ ?
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concept check : bronze is an alloy that can be thought of as a solid solution of ~ $ 88\ % $ copper mixed with $ 12\ % $ tin . what is the solute and solvent in bronze ? example 1 : calculating the molar concentration of a solute let 's consider a solution made by dissolving $ 2.355\ , \text g $ of sulfuric acid , $ \text h_2 \text { so } _4 $ , in water .
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in hint one how do you know there is .1l of solute ?
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key points mixtures with uniform composition are called homogeneous mixtures or solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . introduction : mixtures and solutions in real life , we often encounter substances that are mixtures of different elements and compounds . one example of a mixture is the human body . did you know that the human body is approximately $ 57\ % $ water by mass ? we are basically an assortment of biological molecules , gases , and inorganic ions dissolved in water . i do n't know about you , but i find that pretty mind-boggling ! if substances are mixed together in such a way that the composition is the same throughout the sample , they are called homogeneous mixtures . in contrast , a mixture that does not have a uniform composition throughout the sample is called heterogeneous . homogeneous mixtures are also known as solutions , and solutions can contain components that are solids , liquids and/or gases . we often want to be able to quantify the amount of a species that is in the solution , which is called the concentration of that species . in this article , we 'll look at how to describe solutions quantitatively , and discuss how that information can be used when doing stoichiometric calculations . molar concentration the component of a solution that is present in the largest amount is known as the solvent . any chemical species mixed in the solvent is called a solute , and solutes can be gases , liquids , or solids . for example , earth 's atmosphere is a mixture of $ 78\ % $ nitrogen gas , $ 21\ % $ oxygen gas , and $ 1\ % $ argon , carbon dioxide , and other gases . we can think of the atmosphere as a solution where nitrogen gas is the solvent , and the solutes are oxygen , argon and carbon dioxide . the molarity or molar concentration of a solute is defined as the number of moles of solute per liter of solution ( not per liter of solvent ! ) : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molarity has units of $ \dfrac { \text { mol } } { \text { liter } } $ , which can be abbreviated as molar or $ \text m $ ( pronounced `` molar '' ) . the molar concentration of the solute is sometimes abbreviated by putting square brackets around the chemical formula of the solute . for example , the concentration of chloride ions in a solution can be written as $ [ \text { cl } ^- ] $ . molar concentration allows us to convert between the volume of the solution and the moles ( or mass ) of the solute . concept check : bronze is an alloy that can be thought of as a solid solution of ~ $ 88\ % $ copper mixed with $ 12\ % $ tin . what is the solute and solvent in bronze ? example 1 : calculating the molar concentration of a solute let 's consider a solution made by dissolving $ 2.355\ , \text g $ of sulfuric acid , $ \text h_2 \text { so } _4 $ , in water . the total volume of the solution is $ 50.0\ , \text { ml } $ . what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ? to find $ [ \text h_2 \text { so } _4 ] $ we need to find out how many moles of sulfuric acid are in solution . we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ? example 2 : making a solution with a specific concentration sometimes we have a desired concentration and volume of solution , and we want to know how much solute we need to make the solution . in that case , we can rearrange the molarity equation to solve for the moles of solute . $ \text { mol solute } = { \text { molarity } } \times { \text { l of solution } } $ for example , let 's say we want to make $ 0.250\ , \text { l } $ of an aqueous solution with $ [ \text { nacl } ] =0.800\ , \text { m } $ . what mass of the solute , $ \text { nacl } $ , would we need to make this solution ? we can use the rearranged molarity equation to calculate the moles of $ \text { nacl } $ needed for the specified concentration and volume : $ \begin { align } \text { mol nacl } & amp ; = [ \text { nacl } ] \times { \text { l of solution } } \ & amp ; =0.800\ , \dfrac { \text { mol } } { \cancel { \text l } } \times 0.250\ , \cancel { \text { l } } \ & amp ; =0.200\ , \text { mol nacl } \end { align } $ we can then use the molecular weight of sodium chloride , $ 58.44\ , \dfrac { \text g } { \text { mol } } $ , to convert from moles to grams of $ \text { nacl } $ : $ \text { mass of nacl } =0.200\ , \cancel { \text { mol } } \times \dfrac { 58.44\ , \text g } { 1\ , \cancel { \text { mol } } } = 11.7\ , \text { g nacl } $ in practice , we could use this information to make our solution as follows : step $ 1.~ $ weigh out $ 11.7\ , \text g $ of sodium chloride . step $ 2.~ $ transfer the sodium chloride to a clean , dry flask . step $ 3.~ $ add water to the $ \text { nacl } $ until the total volume of the solution is $ 250\ , \text { ml } $ . step $ 4.~ $ stir until the $ \text { nacl } $ is completely dissolved . the accuracy of our molar concentration depends on our choice of glassware , as well as the accuracy of the balance we use to measure out the solute . the glassware determines the accuracy of our solution volume . if we are n't being too picky , we might mix the solution in a erlenmeyer flask or beaker . if we want to extremely precise , such as when making a standard solution for an analytical chemistry experiment , we would probably mix the solute and solvent in a volumetric flask ( see picture below ) . summary mixtures with uniform composition are called homogeneous solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . try it : the stoichiometry of a precipitation reaction molarity is a useful concept for stoichiometric calculations involving reactions in solution , such precipitation and neutralization reactions . for example , consider the precipitation reaction that occurs between $ \text { pb ( no } _3 ) _2 ( aq ) $ and $ \text { ki } ( aq ) $ . when these two solutions are combined , bright yellow $ \text { pbi } _2 ( s ) $ precipitates out of solution . the balanced equation for this reaction is : $ \text { pb ( no } _3 ) _2 ( aq ) + 2\text { ki } ( aq ) \rightarrow \text { pbi } _2 ( s ) + 2\text { kno } _3 ( aq ) $ if we have $ 0.1\ , \text { l } $ of $ 0.10\ , \text { m pb ( no } _3 ) _2 $ , what volume of $ 0.10\ , \text { m ki } ( aq ) $ should we add to react with all the $ \text { pb ( no } _3 ) _2 ( aq ) $ ?
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one example of a mixture is the human body . did you know that the human body is approximately $ 57\ % $ water by mass ? we are basically an assortment of biological molecules , gases , and inorganic ions dissolved in water . i do n't know about you , but i find that pretty mind-boggling !
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how would you find the molarity of so2 if you have it dissolved in 100 grams of water at 85 degrees celcius ?
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key points mixtures with uniform composition are called homogeneous mixtures or solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . introduction : mixtures and solutions in real life , we often encounter substances that are mixtures of different elements and compounds . one example of a mixture is the human body . did you know that the human body is approximately $ 57\ % $ water by mass ? we are basically an assortment of biological molecules , gases , and inorganic ions dissolved in water . i do n't know about you , but i find that pretty mind-boggling ! if substances are mixed together in such a way that the composition is the same throughout the sample , they are called homogeneous mixtures . in contrast , a mixture that does not have a uniform composition throughout the sample is called heterogeneous . homogeneous mixtures are also known as solutions , and solutions can contain components that are solids , liquids and/or gases . we often want to be able to quantify the amount of a species that is in the solution , which is called the concentration of that species . in this article , we 'll look at how to describe solutions quantitatively , and discuss how that information can be used when doing stoichiometric calculations . molar concentration the component of a solution that is present in the largest amount is known as the solvent . any chemical species mixed in the solvent is called a solute , and solutes can be gases , liquids , or solids . for example , earth 's atmosphere is a mixture of $ 78\ % $ nitrogen gas , $ 21\ % $ oxygen gas , and $ 1\ % $ argon , carbon dioxide , and other gases . we can think of the atmosphere as a solution where nitrogen gas is the solvent , and the solutes are oxygen , argon and carbon dioxide . the molarity or molar concentration of a solute is defined as the number of moles of solute per liter of solution ( not per liter of solvent ! ) : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molarity has units of $ \dfrac { \text { mol } } { \text { liter } } $ , which can be abbreviated as molar or $ \text m $ ( pronounced `` molar '' ) . the molar concentration of the solute is sometimes abbreviated by putting square brackets around the chemical formula of the solute . for example , the concentration of chloride ions in a solution can be written as $ [ \text { cl } ^- ] $ . molar concentration allows us to convert between the volume of the solution and the moles ( or mass ) of the solute . concept check : bronze is an alloy that can be thought of as a solid solution of ~ $ 88\ % $ copper mixed with $ 12\ % $ tin . what is the solute and solvent in bronze ? example 1 : calculating the molar concentration of a solute let 's consider a solution made by dissolving $ 2.355\ , \text g $ of sulfuric acid , $ \text h_2 \text { so } _4 $ , in water . the total volume of the solution is $ 50.0\ , \text { ml } $ . what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ? to find $ [ \text h_2 \text { so } _4 ] $ we need to find out how many moles of sulfuric acid are in solution . we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ? example 2 : making a solution with a specific concentration sometimes we have a desired concentration and volume of solution , and we want to know how much solute we need to make the solution . in that case , we can rearrange the molarity equation to solve for the moles of solute . $ \text { mol solute } = { \text { molarity } } \times { \text { l of solution } } $ for example , let 's say we want to make $ 0.250\ , \text { l } $ of an aqueous solution with $ [ \text { nacl } ] =0.800\ , \text { m } $ . what mass of the solute , $ \text { nacl } $ , would we need to make this solution ? we can use the rearranged molarity equation to calculate the moles of $ \text { nacl } $ needed for the specified concentration and volume : $ \begin { align } \text { mol nacl } & amp ; = [ \text { nacl } ] \times { \text { l of solution } } \ & amp ; =0.800\ , \dfrac { \text { mol } } { \cancel { \text l } } \times 0.250\ , \cancel { \text { l } } \ & amp ; =0.200\ , \text { mol nacl } \end { align } $ we can then use the molecular weight of sodium chloride , $ 58.44\ , \dfrac { \text g } { \text { mol } } $ , to convert from moles to grams of $ \text { nacl } $ : $ \text { mass of nacl } =0.200\ , \cancel { \text { mol } } \times \dfrac { 58.44\ , \text g } { 1\ , \cancel { \text { mol } } } = 11.7\ , \text { g nacl } $ in practice , we could use this information to make our solution as follows : step $ 1.~ $ weigh out $ 11.7\ , \text g $ of sodium chloride . step $ 2.~ $ transfer the sodium chloride to a clean , dry flask . step $ 3.~ $ add water to the $ \text { nacl } $ until the total volume of the solution is $ 250\ , \text { ml } $ . step $ 4.~ $ stir until the $ \text { nacl } $ is completely dissolved . the accuracy of our molar concentration depends on our choice of glassware , as well as the accuracy of the balance we use to measure out the solute . the glassware determines the accuracy of our solution volume . if we are n't being too picky , we might mix the solution in a erlenmeyer flask or beaker . if we want to extremely precise , such as when making a standard solution for an analytical chemistry experiment , we would probably mix the solute and solvent in a volumetric flask ( see picture below ) . summary mixtures with uniform composition are called homogeneous solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . try it : the stoichiometry of a precipitation reaction molarity is a useful concept for stoichiometric calculations involving reactions in solution , such precipitation and neutralization reactions . for example , consider the precipitation reaction that occurs between $ \text { pb ( no } _3 ) _2 ( aq ) $ and $ \text { ki } ( aq ) $ . when these two solutions are combined , bright yellow $ \text { pbi } _2 ( s ) $ precipitates out of solution . the balanced equation for this reaction is : $ \text { pb ( no } _3 ) _2 ( aq ) + 2\text { ki } ( aq ) \rightarrow \text { pbi } _2 ( s ) + 2\text { kno } _3 ( aq ) $ if we have $ 0.1\ , \text { l } $ of $ 0.10\ , \text { m pb ( no } _3 ) _2 $ , what volume of $ 0.10\ , \text { m ki } ( aq ) $ should we add to react with all the $ \text { pb ( no } _3 ) _2 ( aq ) $ ?
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step $ 3.~ $ add water to the $ \text { nacl } $ until the total volume of the solution is $ 250\ , \text { ml } $ . step $ 4.~ $ stir until the $ \text { nacl } $ is completely dissolved . the accuracy of our molar concentration depends on our choice of glassware , as well as the accuracy of the balance we use to measure out the solute .
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( or if the equation happened to have 4ki , could we simply multiply 0.1l x 4 ) ?
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key points mixtures with uniform composition are called homogeneous mixtures or solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . introduction : mixtures and solutions in real life , we often encounter substances that are mixtures of different elements and compounds . one example of a mixture is the human body . did you know that the human body is approximately $ 57\ % $ water by mass ? we are basically an assortment of biological molecules , gases , and inorganic ions dissolved in water . i do n't know about you , but i find that pretty mind-boggling ! if substances are mixed together in such a way that the composition is the same throughout the sample , they are called homogeneous mixtures . in contrast , a mixture that does not have a uniform composition throughout the sample is called heterogeneous . homogeneous mixtures are also known as solutions , and solutions can contain components that are solids , liquids and/or gases . we often want to be able to quantify the amount of a species that is in the solution , which is called the concentration of that species . in this article , we 'll look at how to describe solutions quantitatively , and discuss how that information can be used when doing stoichiometric calculations . molar concentration the component of a solution that is present in the largest amount is known as the solvent . any chemical species mixed in the solvent is called a solute , and solutes can be gases , liquids , or solids . for example , earth 's atmosphere is a mixture of $ 78\ % $ nitrogen gas , $ 21\ % $ oxygen gas , and $ 1\ % $ argon , carbon dioxide , and other gases . we can think of the atmosphere as a solution where nitrogen gas is the solvent , and the solutes are oxygen , argon and carbon dioxide . the molarity or molar concentration of a solute is defined as the number of moles of solute per liter of solution ( not per liter of solvent ! ) : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molarity has units of $ \dfrac { \text { mol } } { \text { liter } } $ , which can be abbreviated as molar or $ \text m $ ( pronounced `` molar '' ) . the molar concentration of the solute is sometimes abbreviated by putting square brackets around the chemical formula of the solute . for example , the concentration of chloride ions in a solution can be written as $ [ \text { cl } ^- ] $ . molar concentration allows us to convert between the volume of the solution and the moles ( or mass ) of the solute . concept check : bronze is an alloy that can be thought of as a solid solution of ~ $ 88\ % $ copper mixed with $ 12\ % $ tin . what is the solute and solvent in bronze ? example 1 : calculating the molar concentration of a solute let 's consider a solution made by dissolving $ 2.355\ , \text g $ of sulfuric acid , $ \text h_2 \text { so } _4 $ , in water . the total volume of the solution is $ 50.0\ , \text { ml } $ . what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ? to find $ [ \text h_2 \text { so } _4 ] $ we need to find out how many moles of sulfuric acid are in solution . we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ? example 2 : making a solution with a specific concentration sometimes we have a desired concentration and volume of solution , and we want to know how much solute we need to make the solution . in that case , we can rearrange the molarity equation to solve for the moles of solute . $ \text { mol solute } = { \text { molarity } } \times { \text { l of solution } } $ for example , let 's say we want to make $ 0.250\ , \text { l } $ of an aqueous solution with $ [ \text { nacl } ] =0.800\ , \text { m } $ . what mass of the solute , $ \text { nacl } $ , would we need to make this solution ? we can use the rearranged molarity equation to calculate the moles of $ \text { nacl } $ needed for the specified concentration and volume : $ \begin { align } \text { mol nacl } & amp ; = [ \text { nacl } ] \times { \text { l of solution } } \ & amp ; =0.800\ , \dfrac { \text { mol } } { \cancel { \text l } } \times 0.250\ , \cancel { \text { l } } \ & amp ; =0.200\ , \text { mol nacl } \end { align } $ we can then use the molecular weight of sodium chloride , $ 58.44\ , \dfrac { \text g } { \text { mol } } $ , to convert from moles to grams of $ \text { nacl } $ : $ \text { mass of nacl } =0.200\ , \cancel { \text { mol } } \times \dfrac { 58.44\ , \text g } { 1\ , \cancel { \text { mol } } } = 11.7\ , \text { g nacl } $ in practice , we could use this information to make our solution as follows : step $ 1.~ $ weigh out $ 11.7\ , \text g $ of sodium chloride . step $ 2.~ $ transfer the sodium chloride to a clean , dry flask . step $ 3.~ $ add water to the $ \text { nacl } $ until the total volume of the solution is $ 250\ , \text { ml } $ . step $ 4.~ $ stir until the $ \text { nacl } $ is completely dissolved . the accuracy of our molar concentration depends on our choice of glassware , as well as the accuracy of the balance we use to measure out the solute . the glassware determines the accuracy of our solution volume . if we are n't being too picky , we might mix the solution in a erlenmeyer flask or beaker . if we want to extremely precise , such as when making a standard solution for an analytical chemistry experiment , we would probably mix the solute and solvent in a volumetric flask ( see picture below ) . summary mixtures with uniform composition are called homogeneous solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . try it : the stoichiometry of a precipitation reaction molarity is a useful concept for stoichiometric calculations involving reactions in solution , such precipitation and neutralization reactions . for example , consider the precipitation reaction that occurs between $ \text { pb ( no } _3 ) _2 ( aq ) $ and $ \text { ki } ( aq ) $ . when these two solutions are combined , bright yellow $ \text { pbi } _2 ( s ) $ precipitates out of solution . the balanced equation for this reaction is : $ \text { pb ( no } _3 ) _2 ( aq ) + 2\text { ki } ( aq ) \rightarrow \text { pbi } _2 ( s ) + 2\text { kno } _3 ( aq ) $ if we have $ 0.1\ , \text { l } $ of $ 0.10\ , \text { m pb ( no } _3 ) _2 $ , what volume of $ 0.10\ , \text { m ki } ( aq ) $ should we add to react with all the $ \text { pb ( no } _3 ) _2 ( aq ) $ ?
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if we want to extremely precise , such as when making a standard solution for an analytical chemistry experiment , we would probably mix the solute and solvent in a volumetric flask ( see picture below ) . summary mixtures with uniform composition are called homogeneous solutions . mixtures with non-uniform composition are heterogeneous mixtures .
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can someone please give me some examples of some heterogeneous and homogeneous things ?
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key points mixtures with uniform composition are called homogeneous mixtures or solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . introduction : mixtures and solutions in real life , we often encounter substances that are mixtures of different elements and compounds . one example of a mixture is the human body . did you know that the human body is approximately $ 57\ % $ water by mass ? we are basically an assortment of biological molecules , gases , and inorganic ions dissolved in water . i do n't know about you , but i find that pretty mind-boggling ! if substances are mixed together in such a way that the composition is the same throughout the sample , they are called homogeneous mixtures . in contrast , a mixture that does not have a uniform composition throughout the sample is called heterogeneous . homogeneous mixtures are also known as solutions , and solutions can contain components that are solids , liquids and/or gases . we often want to be able to quantify the amount of a species that is in the solution , which is called the concentration of that species . in this article , we 'll look at how to describe solutions quantitatively , and discuss how that information can be used when doing stoichiometric calculations . molar concentration the component of a solution that is present in the largest amount is known as the solvent . any chemical species mixed in the solvent is called a solute , and solutes can be gases , liquids , or solids . for example , earth 's atmosphere is a mixture of $ 78\ % $ nitrogen gas , $ 21\ % $ oxygen gas , and $ 1\ % $ argon , carbon dioxide , and other gases . we can think of the atmosphere as a solution where nitrogen gas is the solvent , and the solutes are oxygen , argon and carbon dioxide . the molarity or molar concentration of a solute is defined as the number of moles of solute per liter of solution ( not per liter of solvent ! ) : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molarity has units of $ \dfrac { \text { mol } } { \text { liter } } $ , which can be abbreviated as molar or $ \text m $ ( pronounced `` molar '' ) . the molar concentration of the solute is sometimes abbreviated by putting square brackets around the chemical formula of the solute . for example , the concentration of chloride ions in a solution can be written as $ [ \text { cl } ^- ] $ . molar concentration allows us to convert between the volume of the solution and the moles ( or mass ) of the solute . concept check : bronze is an alloy that can be thought of as a solid solution of ~ $ 88\ % $ copper mixed with $ 12\ % $ tin . what is the solute and solvent in bronze ? example 1 : calculating the molar concentration of a solute let 's consider a solution made by dissolving $ 2.355\ , \text g $ of sulfuric acid , $ \text h_2 \text { so } _4 $ , in water . the total volume of the solution is $ 50.0\ , \text { ml } $ . what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ? to find $ [ \text h_2 \text { so } _4 ] $ we need to find out how many moles of sulfuric acid are in solution . we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ? example 2 : making a solution with a specific concentration sometimes we have a desired concentration and volume of solution , and we want to know how much solute we need to make the solution . in that case , we can rearrange the molarity equation to solve for the moles of solute . $ \text { mol solute } = { \text { molarity } } \times { \text { l of solution } } $ for example , let 's say we want to make $ 0.250\ , \text { l } $ of an aqueous solution with $ [ \text { nacl } ] =0.800\ , \text { m } $ . what mass of the solute , $ \text { nacl } $ , would we need to make this solution ? we can use the rearranged molarity equation to calculate the moles of $ \text { nacl } $ needed for the specified concentration and volume : $ \begin { align } \text { mol nacl } & amp ; = [ \text { nacl } ] \times { \text { l of solution } } \ & amp ; =0.800\ , \dfrac { \text { mol } } { \cancel { \text l } } \times 0.250\ , \cancel { \text { l } } \ & amp ; =0.200\ , \text { mol nacl } \end { align } $ we can then use the molecular weight of sodium chloride , $ 58.44\ , \dfrac { \text g } { \text { mol } } $ , to convert from moles to grams of $ \text { nacl } $ : $ \text { mass of nacl } =0.200\ , \cancel { \text { mol } } \times \dfrac { 58.44\ , \text g } { 1\ , \cancel { \text { mol } } } = 11.7\ , \text { g nacl } $ in practice , we could use this information to make our solution as follows : step $ 1.~ $ weigh out $ 11.7\ , \text g $ of sodium chloride . step $ 2.~ $ transfer the sodium chloride to a clean , dry flask . step $ 3.~ $ add water to the $ \text { nacl } $ until the total volume of the solution is $ 250\ , \text { ml } $ . step $ 4.~ $ stir until the $ \text { nacl } $ is completely dissolved . the accuracy of our molar concentration depends on our choice of glassware , as well as the accuracy of the balance we use to measure out the solute . the glassware determines the accuracy of our solution volume . if we are n't being too picky , we might mix the solution in a erlenmeyer flask or beaker . if we want to extremely precise , such as when making a standard solution for an analytical chemistry experiment , we would probably mix the solute and solvent in a volumetric flask ( see picture below ) . summary mixtures with uniform composition are called homogeneous solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . try it : the stoichiometry of a precipitation reaction molarity is a useful concept for stoichiometric calculations involving reactions in solution , such precipitation and neutralization reactions . for example , consider the precipitation reaction that occurs between $ \text { pb ( no } _3 ) _2 ( aq ) $ and $ \text { ki } ( aq ) $ . when these two solutions are combined , bright yellow $ \text { pbi } _2 ( s ) $ precipitates out of solution . the balanced equation for this reaction is : $ \text { pb ( no } _3 ) _2 ( aq ) + 2\text { ki } ( aq ) \rightarrow \text { pbi } _2 ( s ) + 2\text { kno } _3 ( aq ) $ if we have $ 0.1\ , \text { l } $ of $ 0.10\ , \text { m pb ( no } _3 ) _2 $ , what volume of $ 0.10\ , \text { m ki } ( aq ) $ should we add to react with all the $ \text { pb ( no } _3 ) _2 ( aq ) $ ?
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the total volume of the solution is $ 50.0\ , \text { ml } $ . what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ? to find $ [ \text h_2 \text { so } _4 ] $ we need to find out how many moles of sulfuric acid are in solution .
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so if the sulfuric acid no longer exists in solution after disassociating , then how can we say that the molar concentration of h+ is double the molar concentration of a solute that no longer exists ?
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key points mixtures with uniform composition are called homogeneous mixtures or solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . introduction : mixtures and solutions in real life , we often encounter substances that are mixtures of different elements and compounds . one example of a mixture is the human body . did you know that the human body is approximately $ 57\ % $ water by mass ? we are basically an assortment of biological molecules , gases , and inorganic ions dissolved in water . i do n't know about you , but i find that pretty mind-boggling ! if substances are mixed together in such a way that the composition is the same throughout the sample , they are called homogeneous mixtures . in contrast , a mixture that does not have a uniform composition throughout the sample is called heterogeneous . homogeneous mixtures are also known as solutions , and solutions can contain components that are solids , liquids and/or gases . we often want to be able to quantify the amount of a species that is in the solution , which is called the concentration of that species . in this article , we 'll look at how to describe solutions quantitatively , and discuss how that information can be used when doing stoichiometric calculations . molar concentration the component of a solution that is present in the largest amount is known as the solvent . any chemical species mixed in the solvent is called a solute , and solutes can be gases , liquids , or solids . for example , earth 's atmosphere is a mixture of $ 78\ % $ nitrogen gas , $ 21\ % $ oxygen gas , and $ 1\ % $ argon , carbon dioxide , and other gases . we can think of the atmosphere as a solution where nitrogen gas is the solvent , and the solutes are oxygen , argon and carbon dioxide . the molarity or molar concentration of a solute is defined as the number of moles of solute per liter of solution ( not per liter of solvent ! ) : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molarity has units of $ \dfrac { \text { mol } } { \text { liter } } $ , which can be abbreviated as molar or $ \text m $ ( pronounced `` molar '' ) . the molar concentration of the solute is sometimes abbreviated by putting square brackets around the chemical formula of the solute . for example , the concentration of chloride ions in a solution can be written as $ [ \text { cl } ^- ] $ . molar concentration allows us to convert between the volume of the solution and the moles ( or mass ) of the solute . concept check : bronze is an alloy that can be thought of as a solid solution of ~ $ 88\ % $ copper mixed with $ 12\ % $ tin . what is the solute and solvent in bronze ? example 1 : calculating the molar concentration of a solute let 's consider a solution made by dissolving $ 2.355\ , \text g $ of sulfuric acid , $ \text h_2 \text { so } _4 $ , in water . the total volume of the solution is $ 50.0\ , \text { ml } $ . what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ? to find $ [ \text h_2 \text { so } _4 ] $ we need to find out how many moles of sulfuric acid are in solution . we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ? example 2 : making a solution with a specific concentration sometimes we have a desired concentration and volume of solution , and we want to know how much solute we need to make the solution . in that case , we can rearrange the molarity equation to solve for the moles of solute . $ \text { mol solute } = { \text { molarity } } \times { \text { l of solution } } $ for example , let 's say we want to make $ 0.250\ , \text { l } $ of an aqueous solution with $ [ \text { nacl } ] =0.800\ , \text { m } $ . what mass of the solute , $ \text { nacl } $ , would we need to make this solution ? we can use the rearranged molarity equation to calculate the moles of $ \text { nacl } $ needed for the specified concentration and volume : $ \begin { align } \text { mol nacl } & amp ; = [ \text { nacl } ] \times { \text { l of solution } } \ & amp ; =0.800\ , \dfrac { \text { mol } } { \cancel { \text l } } \times 0.250\ , \cancel { \text { l } } \ & amp ; =0.200\ , \text { mol nacl } \end { align } $ we can then use the molecular weight of sodium chloride , $ 58.44\ , \dfrac { \text g } { \text { mol } } $ , to convert from moles to grams of $ \text { nacl } $ : $ \text { mass of nacl } =0.200\ , \cancel { \text { mol } } \times \dfrac { 58.44\ , \text g } { 1\ , \cancel { \text { mol } } } = 11.7\ , \text { g nacl } $ in practice , we could use this information to make our solution as follows : step $ 1.~ $ weigh out $ 11.7\ , \text g $ of sodium chloride . step $ 2.~ $ transfer the sodium chloride to a clean , dry flask . step $ 3.~ $ add water to the $ \text { nacl } $ until the total volume of the solution is $ 250\ , \text { ml } $ . step $ 4.~ $ stir until the $ \text { nacl } $ is completely dissolved . the accuracy of our molar concentration depends on our choice of glassware , as well as the accuracy of the balance we use to measure out the solute . the glassware determines the accuracy of our solution volume . if we are n't being too picky , we might mix the solution in a erlenmeyer flask or beaker . if we want to extremely precise , such as when making a standard solution for an analytical chemistry experiment , we would probably mix the solute and solvent in a volumetric flask ( see picture below ) . summary mixtures with uniform composition are called homogeneous solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . try it : the stoichiometry of a precipitation reaction molarity is a useful concept for stoichiometric calculations involving reactions in solution , such precipitation and neutralization reactions . for example , consider the precipitation reaction that occurs between $ \text { pb ( no } _3 ) _2 ( aq ) $ and $ \text { ki } ( aq ) $ . when these two solutions are combined , bright yellow $ \text { pbi } _2 ( s ) $ precipitates out of solution . the balanced equation for this reaction is : $ \text { pb ( no } _3 ) _2 ( aq ) + 2\text { ki } ( aq ) \rightarrow \text { pbi } _2 ( s ) + 2\text { kno } _3 ( aq ) $ if we have $ 0.1\ , \text { l } $ of $ 0.10\ , \text { m pb ( no } _3 ) _2 $ , what volume of $ 0.10\ , \text { m ki } ( aq ) $ should we add to react with all the $ \text { pb ( no } _3 ) _2 ( aq ) $ ?
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the molarity or molar concentration of a solute is defined as the number of moles of solute per liter of solution ( not per liter of solvent ! ) : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molarity has units of $ \dfrac { \text { mol } } { \text { liter } } $ , which can be abbreviated as molar or $ \text m $ ( pronounced `` molar '' ) . the molar concentration of the solute is sometimes abbreviated by putting square brackets around the chemical formula of the solute .
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what is the difference between molarity and molality ?
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key points mixtures with uniform composition are called homogeneous mixtures or solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . introduction : mixtures and solutions in real life , we often encounter substances that are mixtures of different elements and compounds . one example of a mixture is the human body . did you know that the human body is approximately $ 57\ % $ water by mass ? we are basically an assortment of biological molecules , gases , and inorganic ions dissolved in water . i do n't know about you , but i find that pretty mind-boggling ! if substances are mixed together in such a way that the composition is the same throughout the sample , they are called homogeneous mixtures . in contrast , a mixture that does not have a uniform composition throughout the sample is called heterogeneous . homogeneous mixtures are also known as solutions , and solutions can contain components that are solids , liquids and/or gases . we often want to be able to quantify the amount of a species that is in the solution , which is called the concentration of that species . in this article , we 'll look at how to describe solutions quantitatively , and discuss how that information can be used when doing stoichiometric calculations . molar concentration the component of a solution that is present in the largest amount is known as the solvent . any chemical species mixed in the solvent is called a solute , and solutes can be gases , liquids , or solids . for example , earth 's atmosphere is a mixture of $ 78\ % $ nitrogen gas , $ 21\ % $ oxygen gas , and $ 1\ % $ argon , carbon dioxide , and other gases . we can think of the atmosphere as a solution where nitrogen gas is the solvent , and the solutes are oxygen , argon and carbon dioxide . the molarity or molar concentration of a solute is defined as the number of moles of solute per liter of solution ( not per liter of solvent ! ) : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molarity has units of $ \dfrac { \text { mol } } { \text { liter } } $ , which can be abbreviated as molar or $ \text m $ ( pronounced `` molar '' ) . the molar concentration of the solute is sometimes abbreviated by putting square brackets around the chemical formula of the solute . for example , the concentration of chloride ions in a solution can be written as $ [ \text { cl } ^- ] $ . molar concentration allows us to convert between the volume of the solution and the moles ( or mass ) of the solute . concept check : bronze is an alloy that can be thought of as a solid solution of ~ $ 88\ % $ copper mixed with $ 12\ % $ tin . what is the solute and solvent in bronze ? example 1 : calculating the molar concentration of a solute let 's consider a solution made by dissolving $ 2.355\ , \text g $ of sulfuric acid , $ \text h_2 \text { so } _4 $ , in water . the total volume of the solution is $ 50.0\ , \text { ml } $ . what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ? to find $ [ \text h_2 \text { so } _4 ] $ we need to find out how many moles of sulfuric acid are in solution . we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ? example 2 : making a solution with a specific concentration sometimes we have a desired concentration and volume of solution , and we want to know how much solute we need to make the solution . in that case , we can rearrange the molarity equation to solve for the moles of solute . $ \text { mol solute } = { \text { molarity } } \times { \text { l of solution } } $ for example , let 's say we want to make $ 0.250\ , \text { l } $ of an aqueous solution with $ [ \text { nacl } ] =0.800\ , \text { m } $ . what mass of the solute , $ \text { nacl } $ , would we need to make this solution ? we can use the rearranged molarity equation to calculate the moles of $ \text { nacl } $ needed for the specified concentration and volume : $ \begin { align } \text { mol nacl } & amp ; = [ \text { nacl } ] \times { \text { l of solution } } \ & amp ; =0.800\ , \dfrac { \text { mol } } { \cancel { \text l } } \times 0.250\ , \cancel { \text { l } } \ & amp ; =0.200\ , \text { mol nacl } \end { align } $ we can then use the molecular weight of sodium chloride , $ 58.44\ , \dfrac { \text g } { \text { mol } } $ , to convert from moles to grams of $ \text { nacl } $ : $ \text { mass of nacl } =0.200\ , \cancel { \text { mol } } \times \dfrac { 58.44\ , \text g } { 1\ , \cancel { \text { mol } } } = 11.7\ , \text { g nacl } $ in practice , we could use this information to make our solution as follows : step $ 1.~ $ weigh out $ 11.7\ , \text g $ of sodium chloride . step $ 2.~ $ transfer the sodium chloride to a clean , dry flask . step $ 3.~ $ add water to the $ \text { nacl } $ until the total volume of the solution is $ 250\ , \text { ml } $ . step $ 4.~ $ stir until the $ \text { nacl } $ is completely dissolved . the accuracy of our molar concentration depends on our choice of glassware , as well as the accuracy of the balance we use to measure out the solute . the glassware determines the accuracy of our solution volume . if we are n't being too picky , we might mix the solution in a erlenmeyer flask or beaker . if we want to extremely precise , such as when making a standard solution for an analytical chemistry experiment , we would probably mix the solute and solvent in a volumetric flask ( see picture below ) . summary mixtures with uniform composition are called homogeneous solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . try it : the stoichiometry of a precipitation reaction molarity is a useful concept for stoichiometric calculations involving reactions in solution , such precipitation and neutralization reactions . for example , consider the precipitation reaction that occurs between $ \text { pb ( no } _3 ) _2 ( aq ) $ and $ \text { ki } ( aq ) $ . when these two solutions are combined , bright yellow $ \text { pbi } _2 ( s ) $ precipitates out of solution . the balanced equation for this reaction is : $ \text { pb ( no } _3 ) _2 ( aq ) + 2\text { ki } ( aq ) \rightarrow \text { pbi } _2 ( s ) + 2\text { kno } _3 ( aq ) $ if we have $ 0.1\ , \text { l } $ of $ 0.10\ , \text { m pb ( no } _3 ) _2 $ , what volume of $ 0.10\ , \text { m ki } ( aq ) $ should we add to react with all the $ \text { pb ( no } _3 ) _2 ( aq ) $ ?
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what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ? to find $ [ \text h_2 \text { so } _4 ] $ we need to find out how many moles of sulfuric acid are in solution . we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ?
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where can i find out how to find the molarity after adding the volumes of 2 solutions ?
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key points mixtures with uniform composition are called homogeneous mixtures or solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . introduction : mixtures and solutions in real life , we often encounter substances that are mixtures of different elements and compounds . one example of a mixture is the human body . did you know that the human body is approximately $ 57\ % $ water by mass ? we are basically an assortment of biological molecules , gases , and inorganic ions dissolved in water . i do n't know about you , but i find that pretty mind-boggling ! if substances are mixed together in such a way that the composition is the same throughout the sample , they are called homogeneous mixtures . in contrast , a mixture that does not have a uniform composition throughout the sample is called heterogeneous . homogeneous mixtures are also known as solutions , and solutions can contain components that are solids , liquids and/or gases . we often want to be able to quantify the amount of a species that is in the solution , which is called the concentration of that species . in this article , we 'll look at how to describe solutions quantitatively , and discuss how that information can be used when doing stoichiometric calculations . molar concentration the component of a solution that is present in the largest amount is known as the solvent . any chemical species mixed in the solvent is called a solute , and solutes can be gases , liquids , or solids . for example , earth 's atmosphere is a mixture of $ 78\ % $ nitrogen gas , $ 21\ % $ oxygen gas , and $ 1\ % $ argon , carbon dioxide , and other gases . we can think of the atmosphere as a solution where nitrogen gas is the solvent , and the solutes are oxygen , argon and carbon dioxide . the molarity or molar concentration of a solute is defined as the number of moles of solute per liter of solution ( not per liter of solvent ! ) : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molarity has units of $ \dfrac { \text { mol } } { \text { liter } } $ , which can be abbreviated as molar or $ \text m $ ( pronounced `` molar '' ) . the molar concentration of the solute is sometimes abbreviated by putting square brackets around the chemical formula of the solute . for example , the concentration of chloride ions in a solution can be written as $ [ \text { cl } ^- ] $ . molar concentration allows us to convert between the volume of the solution and the moles ( or mass ) of the solute . concept check : bronze is an alloy that can be thought of as a solid solution of ~ $ 88\ % $ copper mixed with $ 12\ % $ tin . what is the solute and solvent in bronze ? example 1 : calculating the molar concentration of a solute let 's consider a solution made by dissolving $ 2.355\ , \text g $ of sulfuric acid , $ \text h_2 \text { so } _4 $ , in water . the total volume of the solution is $ 50.0\ , \text { ml } $ . what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ? to find $ [ \text h_2 \text { so } _4 ] $ we need to find out how many moles of sulfuric acid are in solution . we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ? example 2 : making a solution with a specific concentration sometimes we have a desired concentration and volume of solution , and we want to know how much solute we need to make the solution . in that case , we can rearrange the molarity equation to solve for the moles of solute . $ \text { mol solute } = { \text { molarity } } \times { \text { l of solution } } $ for example , let 's say we want to make $ 0.250\ , \text { l } $ of an aqueous solution with $ [ \text { nacl } ] =0.800\ , \text { m } $ . what mass of the solute , $ \text { nacl } $ , would we need to make this solution ? we can use the rearranged molarity equation to calculate the moles of $ \text { nacl } $ needed for the specified concentration and volume : $ \begin { align } \text { mol nacl } & amp ; = [ \text { nacl } ] \times { \text { l of solution } } \ & amp ; =0.800\ , \dfrac { \text { mol } } { \cancel { \text l } } \times 0.250\ , \cancel { \text { l } } \ & amp ; =0.200\ , \text { mol nacl } \end { align } $ we can then use the molecular weight of sodium chloride , $ 58.44\ , \dfrac { \text g } { \text { mol } } $ , to convert from moles to grams of $ \text { nacl } $ : $ \text { mass of nacl } =0.200\ , \cancel { \text { mol } } \times \dfrac { 58.44\ , \text g } { 1\ , \cancel { \text { mol } } } = 11.7\ , \text { g nacl } $ in practice , we could use this information to make our solution as follows : step $ 1.~ $ weigh out $ 11.7\ , \text g $ of sodium chloride . step $ 2.~ $ transfer the sodium chloride to a clean , dry flask . step $ 3.~ $ add water to the $ \text { nacl } $ until the total volume of the solution is $ 250\ , \text { ml } $ . step $ 4.~ $ stir until the $ \text { nacl } $ is completely dissolved . the accuracy of our molar concentration depends on our choice of glassware , as well as the accuracy of the balance we use to measure out the solute . the glassware determines the accuracy of our solution volume . if we are n't being too picky , we might mix the solution in a erlenmeyer flask or beaker . if we want to extremely precise , such as when making a standard solution for an analytical chemistry experiment , we would probably mix the solute and solvent in a volumetric flask ( see picture below ) . summary mixtures with uniform composition are called homogeneous solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . try it : the stoichiometry of a precipitation reaction molarity is a useful concept for stoichiometric calculations involving reactions in solution , such precipitation and neutralization reactions . for example , consider the precipitation reaction that occurs between $ \text { pb ( no } _3 ) _2 ( aq ) $ and $ \text { ki } ( aq ) $ . when these two solutions are combined , bright yellow $ \text { pbi } _2 ( s ) $ precipitates out of solution . the balanced equation for this reaction is : $ \text { pb ( no } _3 ) _2 ( aq ) + 2\text { ki } ( aq ) \rightarrow \text { pbi } _2 ( s ) + 2\text { kno } _3 ( aq ) $ if we have $ 0.1\ , \text { l } $ of $ 0.10\ , \text { m pb ( no } _3 ) _2 $ , what volume of $ 0.10\ , \text { m ki } ( aq ) $ should we add to react with all the $ \text { pb ( no } _3 ) _2 ( aq ) $ ?
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example 1 : calculating the molar concentration of a solute let 's consider a solution made by dissolving $ 2.355\ , \text g $ of sulfuric acid , $ \text h_2 \text { so } _4 $ , in water . the total volume of the solution is $ 50.0\ , \text { ml } $ . what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ?
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what is the molarity of a kcl solution made by diluting 75.0 ml of a 0.200 m solution to a final volume of 100. ml ?
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key points mixtures with uniform composition are called homogeneous mixtures or solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . introduction : mixtures and solutions in real life , we often encounter substances that are mixtures of different elements and compounds . one example of a mixture is the human body . did you know that the human body is approximately $ 57\ % $ water by mass ? we are basically an assortment of biological molecules , gases , and inorganic ions dissolved in water . i do n't know about you , but i find that pretty mind-boggling ! if substances are mixed together in such a way that the composition is the same throughout the sample , they are called homogeneous mixtures . in contrast , a mixture that does not have a uniform composition throughout the sample is called heterogeneous . homogeneous mixtures are also known as solutions , and solutions can contain components that are solids , liquids and/or gases . we often want to be able to quantify the amount of a species that is in the solution , which is called the concentration of that species . in this article , we 'll look at how to describe solutions quantitatively , and discuss how that information can be used when doing stoichiometric calculations . molar concentration the component of a solution that is present in the largest amount is known as the solvent . any chemical species mixed in the solvent is called a solute , and solutes can be gases , liquids , or solids . for example , earth 's atmosphere is a mixture of $ 78\ % $ nitrogen gas , $ 21\ % $ oxygen gas , and $ 1\ % $ argon , carbon dioxide , and other gases . we can think of the atmosphere as a solution where nitrogen gas is the solvent , and the solutes are oxygen , argon and carbon dioxide . the molarity or molar concentration of a solute is defined as the number of moles of solute per liter of solution ( not per liter of solvent ! ) : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molarity has units of $ \dfrac { \text { mol } } { \text { liter } } $ , which can be abbreviated as molar or $ \text m $ ( pronounced `` molar '' ) . the molar concentration of the solute is sometimes abbreviated by putting square brackets around the chemical formula of the solute . for example , the concentration of chloride ions in a solution can be written as $ [ \text { cl } ^- ] $ . molar concentration allows us to convert between the volume of the solution and the moles ( or mass ) of the solute . concept check : bronze is an alloy that can be thought of as a solid solution of ~ $ 88\ % $ copper mixed with $ 12\ % $ tin . what is the solute and solvent in bronze ? example 1 : calculating the molar concentration of a solute let 's consider a solution made by dissolving $ 2.355\ , \text g $ of sulfuric acid , $ \text h_2 \text { so } _4 $ , in water . the total volume of the solution is $ 50.0\ , \text { ml } $ . what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ? to find $ [ \text h_2 \text { so } _4 ] $ we need to find out how many moles of sulfuric acid are in solution . we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ? example 2 : making a solution with a specific concentration sometimes we have a desired concentration and volume of solution , and we want to know how much solute we need to make the solution . in that case , we can rearrange the molarity equation to solve for the moles of solute . $ \text { mol solute } = { \text { molarity } } \times { \text { l of solution } } $ for example , let 's say we want to make $ 0.250\ , \text { l } $ of an aqueous solution with $ [ \text { nacl } ] =0.800\ , \text { m } $ . what mass of the solute , $ \text { nacl } $ , would we need to make this solution ? we can use the rearranged molarity equation to calculate the moles of $ \text { nacl } $ needed for the specified concentration and volume : $ \begin { align } \text { mol nacl } & amp ; = [ \text { nacl } ] \times { \text { l of solution } } \ & amp ; =0.800\ , \dfrac { \text { mol } } { \cancel { \text l } } \times 0.250\ , \cancel { \text { l } } \ & amp ; =0.200\ , \text { mol nacl } \end { align } $ we can then use the molecular weight of sodium chloride , $ 58.44\ , \dfrac { \text g } { \text { mol } } $ , to convert from moles to grams of $ \text { nacl } $ : $ \text { mass of nacl } =0.200\ , \cancel { \text { mol } } \times \dfrac { 58.44\ , \text g } { 1\ , \cancel { \text { mol } } } = 11.7\ , \text { g nacl } $ in practice , we could use this information to make our solution as follows : step $ 1.~ $ weigh out $ 11.7\ , \text g $ of sodium chloride . step $ 2.~ $ transfer the sodium chloride to a clean , dry flask . step $ 3.~ $ add water to the $ \text { nacl } $ until the total volume of the solution is $ 250\ , \text { ml } $ . step $ 4.~ $ stir until the $ \text { nacl } $ is completely dissolved . the accuracy of our molar concentration depends on our choice of glassware , as well as the accuracy of the balance we use to measure out the solute . the glassware determines the accuracy of our solution volume . if we are n't being too picky , we might mix the solution in a erlenmeyer flask or beaker . if we want to extremely precise , such as when making a standard solution for an analytical chemistry experiment , we would probably mix the solute and solvent in a volumetric flask ( see picture below ) . summary mixtures with uniform composition are called homogeneous solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . try it : the stoichiometry of a precipitation reaction molarity is a useful concept for stoichiometric calculations involving reactions in solution , such precipitation and neutralization reactions . for example , consider the precipitation reaction that occurs between $ \text { pb ( no } _3 ) _2 ( aq ) $ and $ \text { ki } ( aq ) $ . when these two solutions are combined , bright yellow $ \text { pbi } _2 ( s ) $ precipitates out of solution . the balanced equation for this reaction is : $ \text { pb ( no } _3 ) _2 ( aq ) + 2\text { ki } ( aq ) \rightarrow \text { pbi } _2 ( s ) + 2\text { kno } _3 ( aq ) $ if we have $ 0.1\ , \text { l } $ of $ 0.10\ , \text { m pb ( no } _3 ) _2 $ , what volume of $ 0.10\ , \text { m ki } ( aq ) $ should we add to react with all the $ \text { pb ( no } _3 ) _2 ( aq ) $ ?
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we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ? example 2 : making a solution with a specific concentration sometimes we have a desired concentration and volume of solution , and we want to know how much solute we need to make the solution . in that case , we can rearrange the molarity equation to solve for the moles of solute .
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how do i know the concentration of solute in the entire solution ?
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key points mixtures with uniform composition are called homogeneous mixtures or solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . introduction : mixtures and solutions in real life , we often encounter substances that are mixtures of different elements and compounds . one example of a mixture is the human body . did you know that the human body is approximately $ 57\ % $ water by mass ? we are basically an assortment of biological molecules , gases , and inorganic ions dissolved in water . i do n't know about you , but i find that pretty mind-boggling ! if substances are mixed together in such a way that the composition is the same throughout the sample , they are called homogeneous mixtures . in contrast , a mixture that does not have a uniform composition throughout the sample is called heterogeneous . homogeneous mixtures are also known as solutions , and solutions can contain components that are solids , liquids and/or gases . we often want to be able to quantify the amount of a species that is in the solution , which is called the concentration of that species . in this article , we 'll look at how to describe solutions quantitatively , and discuss how that information can be used when doing stoichiometric calculations . molar concentration the component of a solution that is present in the largest amount is known as the solvent . any chemical species mixed in the solvent is called a solute , and solutes can be gases , liquids , or solids . for example , earth 's atmosphere is a mixture of $ 78\ % $ nitrogen gas , $ 21\ % $ oxygen gas , and $ 1\ % $ argon , carbon dioxide , and other gases . we can think of the atmosphere as a solution where nitrogen gas is the solvent , and the solutes are oxygen , argon and carbon dioxide . the molarity or molar concentration of a solute is defined as the number of moles of solute per liter of solution ( not per liter of solvent ! ) : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molarity has units of $ \dfrac { \text { mol } } { \text { liter } } $ , which can be abbreviated as molar or $ \text m $ ( pronounced `` molar '' ) . the molar concentration of the solute is sometimes abbreviated by putting square brackets around the chemical formula of the solute . for example , the concentration of chloride ions in a solution can be written as $ [ \text { cl } ^- ] $ . molar concentration allows us to convert between the volume of the solution and the moles ( or mass ) of the solute . concept check : bronze is an alloy that can be thought of as a solid solution of ~ $ 88\ % $ copper mixed with $ 12\ % $ tin . what is the solute and solvent in bronze ? example 1 : calculating the molar concentration of a solute let 's consider a solution made by dissolving $ 2.355\ , \text g $ of sulfuric acid , $ \text h_2 \text { so } _4 $ , in water . the total volume of the solution is $ 50.0\ , \text { ml } $ . what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ? to find $ [ \text h_2 \text { so } _4 ] $ we need to find out how many moles of sulfuric acid are in solution . we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ? example 2 : making a solution with a specific concentration sometimes we have a desired concentration and volume of solution , and we want to know how much solute we need to make the solution . in that case , we can rearrange the molarity equation to solve for the moles of solute . $ \text { mol solute } = { \text { molarity } } \times { \text { l of solution } } $ for example , let 's say we want to make $ 0.250\ , \text { l } $ of an aqueous solution with $ [ \text { nacl } ] =0.800\ , \text { m } $ . what mass of the solute , $ \text { nacl } $ , would we need to make this solution ? we can use the rearranged molarity equation to calculate the moles of $ \text { nacl } $ needed for the specified concentration and volume : $ \begin { align } \text { mol nacl } & amp ; = [ \text { nacl } ] \times { \text { l of solution } } \ & amp ; =0.800\ , \dfrac { \text { mol } } { \cancel { \text l } } \times 0.250\ , \cancel { \text { l } } \ & amp ; =0.200\ , \text { mol nacl } \end { align } $ we can then use the molecular weight of sodium chloride , $ 58.44\ , \dfrac { \text g } { \text { mol } } $ , to convert from moles to grams of $ \text { nacl } $ : $ \text { mass of nacl } =0.200\ , \cancel { \text { mol } } \times \dfrac { 58.44\ , \text g } { 1\ , \cancel { \text { mol } } } = 11.7\ , \text { g nacl } $ in practice , we could use this information to make our solution as follows : step $ 1.~ $ weigh out $ 11.7\ , \text g $ of sodium chloride . step $ 2.~ $ transfer the sodium chloride to a clean , dry flask . step $ 3.~ $ add water to the $ \text { nacl } $ until the total volume of the solution is $ 250\ , \text { ml } $ . step $ 4.~ $ stir until the $ \text { nacl } $ is completely dissolved . the accuracy of our molar concentration depends on our choice of glassware , as well as the accuracy of the balance we use to measure out the solute . the glassware determines the accuracy of our solution volume . if we are n't being too picky , we might mix the solution in a erlenmeyer flask or beaker . if we want to extremely precise , such as when making a standard solution for an analytical chemistry experiment , we would probably mix the solute and solvent in a volumetric flask ( see picture below ) . summary mixtures with uniform composition are called homogeneous solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . try it : the stoichiometry of a precipitation reaction molarity is a useful concept for stoichiometric calculations involving reactions in solution , such precipitation and neutralization reactions . for example , consider the precipitation reaction that occurs between $ \text { pb ( no } _3 ) _2 ( aq ) $ and $ \text { ki } ( aq ) $ . when these two solutions are combined , bright yellow $ \text { pbi } _2 ( s ) $ precipitates out of solution . the balanced equation for this reaction is : $ \text { pb ( no } _3 ) _2 ( aq ) + 2\text { ki } ( aq ) \rightarrow \text { pbi } _2 ( s ) + 2\text { kno } _3 ( aq ) $ if we have $ 0.1\ , \text { l } $ of $ 0.10\ , \text { m pb ( no } _3 ) _2 $ , what volume of $ 0.10\ , \text { m ki } ( aq ) $ should we add to react with all the $ \text { pb ( no } _3 ) _2 ( aq ) $ ?
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the molar concentration of the solute is sometimes abbreviated by putting square brackets around the chemical formula of the solute . for example , the concentration of chloride ions in a solution can be written as $ [ \text { cl } ^- ] $ . molar concentration allows us to convert between the volume of the solution and the moles ( or mass ) of the solute .
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how do i determine the molarity of magnesium ions in a solution ?
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key points mixtures with uniform composition are called homogeneous mixtures or solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . introduction : mixtures and solutions in real life , we often encounter substances that are mixtures of different elements and compounds . one example of a mixture is the human body . did you know that the human body is approximately $ 57\ % $ water by mass ? we are basically an assortment of biological molecules , gases , and inorganic ions dissolved in water . i do n't know about you , but i find that pretty mind-boggling ! if substances are mixed together in such a way that the composition is the same throughout the sample , they are called homogeneous mixtures . in contrast , a mixture that does not have a uniform composition throughout the sample is called heterogeneous . homogeneous mixtures are also known as solutions , and solutions can contain components that are solids , liquids and/or gases . we often want to be able to quantify the amount of a species that is in the solution , which is called the concentration of that species . in this article , we 'll look at how to describe solutions quantitatively , and discuss how that information can be used when doing stoichiometric calculations . molar concentration the component of a solution that is present in the largest amount is known as the solvent . any chemical species mixed in the solvent is called a solute , and solutes can be gases , liquids , or solids . for example , earth 's atmosphere is a mixture of $ 78\ % $ nitrogen gas , $ 21\ % $ oxygen gas , and $ 1\ % $ argon , carbon dioxide , and other gases . we can think of the atmosphere as a solution where nitrogen gas is the solvent , and the solutes are oxygen , argon and carbon dioxide . the molarity or molar concentration of a solute is defined as the number of moles of solute per liter of solution ( not per liter of solvent ! ) : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molarity has units of $ \dfrac { \text { mol } } { \text { liter } } $ , which can be abbreviated as molar or $ \text m $ ( pronounced `` molar '' ) . the molar concentration of the solute is sometimes abbreviated by putting square brackets around the chemical formula of the solute . for example , the concentration of chloride ions in a solution can be written as $ [ \text { cl } ^- ] $ . molar concentration allows us to convert between the volume of the solution and the moles ( or mass ) of the solute . concept check : bronze is an alloy that can be thought of as a solid solution of ~ $ 88\ % $ copper mixed with $ 12\ % $ tin . what is the solute and solvent in bronze ? example 1 : calculating the molar concentration of a solute let 's consider a solution made by dissolving $ 2.355\ , \text g $ of sulfuric acid , $ \text h_2 \text { so } _4 $ , in water . the total volume of the solution is $ 50.0\ , \text { ml } $ . what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ? to find $ [ \text h_2 \text { so } _4 ] $ we need to find out how many moles of sulfuric acid are in solution . we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ? example 2 : making a solution with a specific concentration sometimes we have a desired concentration and volume of solution , and we want to know how much solute we need to make the solution . in that case , we can rearrange the molarity equation to solve for the moles of solute . $ \text { mol solute } = { \text { molarity } } \times { \text { l of solution } } $ for example , let 's say we want to make $ 0.250\ , \text { l } $ of an aqueous solution with $ [ \text { nacl } ] =0.800\ , \text { m } $ . what mass of the solute , $ \text { nacl } $ , would we need to make this solution ? we can use the rearranged molarity equation to calculate the moles of $ \text { nacl } $ needed for the specified concentration and volume : $ \begin { align } \text { mol nacl } & amp ; = [ \text { nacl } ] \times { \text { l of solution } } \ & amp ; =0.800\ , \dfrac { \text { mol } } { \cancel { \text l } } \times 0.250\ , \cancel { \text { l } } \ & amp ; =0.200\ , \text { mol nacl } \end { align } $ we can then use the molecular weight of sodium chloride , $ 58.44\ , \dfrac { \text g } { \text { mol } } $ , to convert from moles to grams of $ \text { nacl } $ : $ \text { mass of nacl } =0.200\ , \cancel { \text { mol } } \times \dfrac { 58.44\ , \text g } { 1\ , \cancel { \text { mol } } } = 11.7\ , \text { g nacl } $ in practice , we could use this information to make our solution as follows : step $ 1.~ $ weigh out $ 11.7\ , \text g $ of sodium chloride . step $ 2.~ $ transfer the sodium chloride to a clean , dry flask . step $ 3.~ $ add water to the $ \text { nacl } $ until the total volume of the solution is $ 250\ , \text { ml } $ . step $ 4.~ $ stir until the $ \text { nacl } $ is completely dissolved . the accuracy of our molar concentration depends on our choice of glassware , as well as the accuracy of the balance we use to measure out the solute . the glassware determines the accuracy of our solution volume . if we are n't being too picky , we might mix the solution in a erlenmeyer flask or beaker . if we want to extremely precise , such as when making a standard solution for an analytical chemistry experiment , we would probably mix the solute and solvent in a volumetric flask ( see picture below ) . summary mixtures with uniform composition are called homogeneous solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . try it : the stoichiometry of a precipitation reaction molarity is a useful concept for stoichiometric calculations involving reactions in solution , such precipitation and neutralization reactions . for example , consider the precipitation reaction that occurs between $ \text { pb ( no } _3 ) _2 ( aq ) $ and $ \text { ki } ( aq ) $ . when these two solutions are combined , bright yellow $ \text { pbi } _2 ( s ) $ precipitates out of solution . the balanced equation for this reaction is : $ \text { pb ( no } _3 ) _2 ( aq ) + 2\text { ki } ( aq ) \rightarrow \text { pbi } _2 ( s ) + 2\text { kno } _3 ( aq ) $ if we have $ 0.1\ , \text { l } $ of $ 0.10\ , \text { m pb ( no } _3 ) _2 $ , what volume of $ 0.10\ , \text { m ki } ( aq ) $ should we add to react with all the $ \text { pb ( no } _3 ) _2 ( aq ) $ ?
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we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ? example 2 : making a solution with a specific concentration sometimes we have a desired concentration and volume of solution , and we want to know how much solute we need to make the solution . in that case , we can rearrange the molarity equation to solve for the moles of solute .
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what is the molar concentration of this solution ?
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key points mixtures with uniform composition are called homogeneous mixtures or solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . introduction : mixtures and solutions in real life , we often encounter substances that are mixtures of different elements and compounds . one example of a mixture is the human body . did you know that the human body is approximately $ 57\ % $ water by mass ? we are basically an assortment of biological molecules , gases , and inorganic ions dissolved in water . i do n't know about you , but i find that pretty mind-boggling ! if substances are mixed together in such a way that the composition is the same throughout the sample , they are called homogeneous mixtures . in contrast , a mixture that does not have a uniform composition throughout the sample is called heterogeneous . homogeneous mixtures are also known as solutions , and solutions can contain components that are solids , liquids and/or gases . we often want to be able to quantify the amount of a species that is in the solution , which is called the concentration of that species . in this article , we 'll look at how to describe solutions quantitatively , and discuss how that information can be used when doing stoichiometric calculations . molar concentration the component of a solution that is present in the largest amount is known as the solvent . any chemical species mixed in the solvent is called a solute , and solutes can be gases , liquids , or solids . for example , earth 's atmosphere is a mixture of $ 78\ % $ nitrogen gas , $ 21\ % $ oxygen gas , and $ 1\ % $ argon , carbon dioxide , and other gases . we can think of the atmosphere as a solution where nitrogen gas is the solvent , and the solutes are oxygen , argon and carbon dioxide . the molarity or molar concentration of a solute is defined as the number of moles of solute per liter of solution ( not per liter of solvent ! ) : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molarity has units of $ \dfrac { \text { mol } } { \text { liter } } $ , which can be abbreviated as molar or $ \text m $ ( pronounced `` molar '' ) . the molar concentration of the solute is sometimes abbreviated by putting square brackets around the chemical formula of the solute . for example , the concentration of chloride ions in a solution can be written as $ [ \text { cl } ^- ] $ . molar concentration allows us to convert between the volume of the solution and the moles ( or mass ) of the solute . concept check : bronze is an alloy that can be thought of as a solid solution of ~ $ 88\ % $ copper mixed with $ 12\ % $ tin . what is the solute and solvent in bronze ? example 1 : calculating the molar concentration of a solute let 's consider a solution made by dissolving $ 2.355\ , \text g $ of sulfuric acid , $ \text h_2 \text { so } _4 $ , in water . the total volume of the solution is $ 50.0\ , \text { ml } $ . what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ? to find $ [ \text h_2 \text { so } _4 ] $ we need to find out how many moles of sulfuric acid are in solution . we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ? example 2 : making a solution with a specific concentration sometimes we have a desired concentration and volume of solution , and we want to know how much solute we need to make the solution . in that case , we can rearrange the molarity equation to solve for the moles of solute . $ \text { mol solute } = { \text { molarity } } \times { \text { l of solution } } $ for example , let 's say we want to make $ 0.250\ , \text { l } $ of an aqueous solution with $ [ \text { nacl } ] =0.800\ , \text { m } $ . what mass of the solute , $ \text { nacl } $ , would we need to make this solution ? we can use the rearranged molarity equation to calculate the moles of $ \text { nacl } $ needed for the specified concentration and volume : $ \begin { align } \text { mol nacl } & amp ; = [ \text { nacl } ] \times { \text { l of solution } } \ & amp ; =0.800\ , \dfrac { \text { mol } } { \cancel { \text l } } \times 0.250\ , \cancel { \text { l } } \ & amp ; =0.200\ , \text { mol nacl } \end { align } $ we can then use the molecular weight of sodium chloride , $ 58.44\ , \dfrac { \text g } { \text { mol } } $ , to convert from moles to grams of $ \text { nacl } $ : $ \text { mass of nacl } =0.200\ , \cancel { \text { mol } } \times \dfrac { 58.44\ , \text g } { 1\ , \cancel { \text { mol } } } = 11.7\ , \text { g nacl } $ in practice , we could use this information to make our solution as follows : step $ 1.~ $ weigh out $ 11.7\ , \text g $ of sodium chloride . step $ 2.~ $ transfer the sodium chloride to a clean , dry flask . step $ 3.~ $ add water to the $ \text { nacl } $ until the total volume of the solution is $ 250\ , \text { ml } $ . step $ 4.~ $ stir until the $ \text { nacl } $ is completely dissolved . the accuracy of our molar concentration depends on our choice of glassware , as well as the accuracy of the balance we use to measure out the solute . the glassware determines the accuracy of our solution volume . if we are n't being too picky , we might mix the solution in a erlenmeyer flask or beaker . if we want to extremely precise , such as when making a standard solution for an analytical chemistry experiment , we would probably mix the solute and solvent in a volumetric flask ( see picture below ) . summary mixtures with uniform composition are called homogeneous solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . try it : the stoichiometry of a precipitation reaction molarity is a useful concept for stoichiometric calculations involving reactions in solution , such precipitation and neutralization reactions . for example , consider the precipitation reaction that occurs between $ \text { pb ( no } _3 ) _2 ( aq ) $ and $ \text { ki } ( aq ) $ . when these two solutions are combined , bright yellow $ \text { pbi } _2 ( s ) $ precipitates out of solution . the balanced equation for this reaction is : $ \text { pb ( no } _3 ) _2 ( aq ) + 2\text { ki } ( aq ) \rightarrow \text { pbi } _2 ( s ) + 2\text { kno } _3 ( aq ) $ if we have $ 0.1\ , \text { l } $ of $ 0.10\ , \text { m pb ( no } _3 ) _2 $ , what volume of $ 0.10\ , \text { m ki } ( aq ) $ should we add to react with all the $ \text { pb ( no } _3 ) _2 ( aq ) $ ?
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what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ? to find $ [ \text h_2 \text { so } _4 ] $ we need to find out how many moles of sulfuric acid are in solution . we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ?
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how do you find the molarity of the ions in the compound ?
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key points mixtures with uniform composition are called homogeneous mixtures or solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . introduction : mixtures and solutions in real life , we often encounter substances that are mixtures of different elements and compounds . one example of a mixture is the human body . did you know that the human body is approximately $ 57\ % $ water by mass ? we are basically an assortment of biological molecules , gases , and inorganic ions dissolved in water . i do n't know about you , but i find that pretty mind-boggling ! if substances are mixed together in such a way that the composition is the same throughout the sample , they are called homogeneous mixtures . in contrast , a mixture that does not have a uniform composition throughout the sample is called heterogeneous . homogeneous mixtures are also known as solutions , and solutions can contain components that are solids , liquids and/or gases . we often want to be able to quantify the amount of a species that is in the solution , which is called the concentration of that species . in this article , we 'll look at how to describe solutions quantitatively , and discuss how that information can be used when doing stoichiometric calculations . molar concentration the component of a solution that is present in the largest amount is known as the solvent . any chemical species mixed in the solvent is called a solute , and solutes can be gases , liquids , or solids . for example , earth 's atmosphere is a mixture of $ 78\ % $ nitrogen gas , $ 21\ % $ oxygen gas , and $ 1\ % $ argon , carbon dioxide , and other gases . we can think of the atmosphere as a solution where nitrogen gas is the solvent , and the solutes are oxygen , argon and carbon dioxide . the molarity or molar concentration of a solute is defined as the number of moles of solute per liter of solution ( not per liter of solvent ! ) : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molarity has units of $ \dfrac { \text { mol } } { \text { liter } } $ , which can be abbreviated as molar or $ \text m $ ( pronounced `` molar '' ) . the molar concentration of the solute is sometimes abbreviated by putting square brackets around the chemical formula of the solute . for example , the concentration of chloride ions in a solution can be written as $ [ \text { cl } ^- ] $ . molar concentration allows us to convert between the volume of the solution and the moles ( or mass ) of the solute . concept check : bronze is an alloy that can be thought of as a solid solution of ~ $ 88\ % $ copper mixed with $ 12\ % $ tin . what is the solute and solvent in bronze ? example 1 : calculating the molar concentration of a solute let 's consider a solution made by dissolving $ 2.355\ , \text g $ of sulfuric acid , $ \text h_2 \text { so } _4 $ , in water . the total volume of the solution is $ 50.0\ , \text { ml } $ . what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ? to find $ [ \text h_2 \text { so } _4 ] $ we need to find out how many moles of sulfuric acid are in solution . we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ? example 2 : making a solution with a specific concentration sometimes we have a desired concentration and volume of solution , and we want to know how much solute we need to make the solution . in that case , we can rearrange the molarity equation to solve for the moles of solute . $ \text { mol solute } = { \text { molarity } } \times { \text { l of solution } } $ for example , let 's say we want to make $ 0.250\ , \text { l } $ of an aqueous solution with $ [ \text { nacl } ] =0.800\ , \text { m } $ . what mass of the solute , $ \text { nacl } $ , would we need to make this solution ? we can use the rearranged molarity equation to calculate the moles of $ \text { nacl } $ needed for the specified concentration and volume : $ \begin { align } \text { mol nacl } & amp ; = [ \text { nacl } ] \times { \text { l of solution } } \ & amp ; =0.800\ , \dfrac { \text { mol } } { \cancel { \text l } } \times 0.250\ , \cancel { \text { l } } \ & amp ; =0.200\ , \text { mol nacl } \end { align } $ we can then use the molecular weight of sodium chloride , $ 58.44\ , \dfrac { \text g } { \text { mol } } $ , to convert from moles to grams of $ \text { nacl } $ : $ \text { mass of nacl } =0.200\ , \cancel { \text { mol } } \times \dfrac { 58.44\ , \text g } { 1\ , \cancel { \text { mol } } } = 11.7\ , \text { g nacl } $ in practice , we could use this information to make our solution as follows : step $ 1.~ $ weigh out $ 11.7\ , \text g $ of sodium chloride . step $ 2.~ $ transfer the sodium chloride to a clean , dry flask . step $ 3.~ $ add water to the $ \text { nacl } $ until the total volume of the solution is $ 250\ , \text { ml } $ . step $ 4.~ $ stir until the $ \text { nacl } $ is completely dissolved . the accuracy of our molar concentration depends on our choice of glassware , as well as the accuracy of the balance we use to measure out the solute . the glassware determines the accuracy of our solution volume . if we are n't being too picky , we might mix the solution in a erlenmeyer flask or beaker . if we want to extremely precise , such as when making a standard solution for an analytical chemistry experiment , we would probably mix the solute and solvent in a volumetric flask ( see picture below ) . summary mixtures with uniform composition are called homogeneous solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . try it : the stoichiometry of a precipitation reaction molarity is a useful concept for stoichiometric calculations involving reactions in solution , such precipitation and neutralization reactions . for example , consider the precipitation reaction that occurs between $ \text { pb ( no } _3 ) _2 ( aq ) $ and $ \text { ki } ( aq ) $ . when these two solutions are combined , bright yellow $ \text { pbi } _2 ( s ) $ precipitates out of solution . the balanced equation for this reaction is : $ \text { pb ( no } _3 ) _2 ( aq ) + 2\text { ki } ( aq ) \rightarrow \text { pbi } _2 ( s ) + 2\text { kno } _3 ( aq ) $ if we have $ 0.1\ , \text { l } $ of $ 0.10\ , \text { m pb ( no } _3 ) _2 $ , what volume of $ 0.10\ , \text { m ki } ( aq ) $ should we add to react with all the $ \text { pb ( no } _3 ) _2 ( aq ) $ ?
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example 1 : calculating the molar concentration of a solute let 's consider a solution made by dissolving $ 2.355\ , \text g $ of sulfuric acid , $ \text h_2 \text { so } _4 $ , in water . the total volume of the solution is $ 50.0\ , \text { ml } $ . what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ?
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if there is 3 ml of salt dissolved in 18 ml of acid , the concentration of the solution is ?
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key points mixtures with uniform composition are called homogeneous mixtures or solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . introduction : mixtures and solutions in real life , we often encounter substances that are mixtures of different elements and compounds . one example of a mixture is the human body . did you know that the human body is approximately $ 57\ % $ water by mass ? we are basically an assortment of biological molecules , gases , and inorganic ions dissolved in water . i do n't know about you , but i find that pretty mind-boggling ! if substances are mixed together in such a way that the composition is the same throughout the sample , they are called homogeneous mixtures . in contrast , a mixture that does not have a uniform composition throughout the sample is called heterogeneous . homogeneous mixtures are also known as solutions , and solutions can contain components that are solids , liquids and/or gases . we often want to be able to quantify the amount of a species that is in the solution , which is called the concentration of that species . in this article , we 'll look at how to describe solutions quantitatively , and discuss how that information can be used when doing stoichiometric calculations . molar concentration the component of a solution that is present in the largest amount is known as the solvent . any chemical species mixed in the solvent is called a solute , and solutes can be gases , liquids , or solids . for example , earth 's atmosphere is a mixture of $ 78\ % $ nitrogen gas , $ 21\ % $ oxygen gas , and $ 1\ % $ argon , carbon dioxide , and other gases . we can think of the atmosphere as a solution where nitrogen gas is the solvent , and the solutes are oxygen , argon and carbon dioxide . the molarity or molar concentration of a solute is defined as the number of moles of solute per liter of solution ( not per liter of solvent ! ) : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molarity has units of $ \dfrac { \text { mol } } { \text { liter } } $ , which can be abbreviated as molar or $ \text m $ ( pronounced `` molar '' ) . the molar concentration of the solute is sometimes abbreviated by putting square brackets around the chemical formula of the solute . for example , the concentration of chloride ions in a solution can be written as $ [ \text { cl } ^- ] $ . molar concentration allows us to convert between the volume of the solution and the moles ( or mass ) of the solute . concept check : bronze is an alloy that can be thought of as a solid solution of ~ $ 88\ % $ copper mixed with $ 12\ % $ tin . what is the solute and solvent in bronze ? example 1 : calculating the molar concentration of a solute let 's consider a solution made by dissolving $ 2.355\ , \text g $ of sulfuric acid , $ \text h_2 \text { so } _4 $ , in water . the total volume of the solution is $ 50.0\ , \text { ml } $ . what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ? to find $ [ \text h_2 \text { so } _4 ] $ we need to find out how many moles of sulfuric acid are in solution . we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ? example 2 : making a solution with a specific concentration sometimes we have a desired concentration and volume of solution , and we want to know how much solute we need to make the solution . in that case , we can rearrange the molarity equation to solve for the moles of solute . $ \text { mol solute } = { \text { molarity } } \times { \text { l of solution } } $ for example , let 's say we want to make $ 0.250\ , \text { l } $ of an aqueous solution with $ [ \text { nacl } ] =0.800\ , \text { m } $ . what mass of the solute , $ \text { nacl } $ , would we need to make this solution ? we can use the rearranged molarity equation to calculate the moles of $ \text { nacl } $ needed for the specified concentration and volume : $ \begin { align } \text { mol nacl } & amp ; = [ \text { nacl } ] \times { \text { l of solution } } \ & amp ; =0.800\ , \dfrac { \text { mol } } { \cancel { \text l } } \times 0.250\ , \cancel { \text { l } } \ & amp ; =0.200\ , \text { mol nacl } \end { align } $ we can then use the molecular weight of sodium chloride , $ 58.44\ , \dfrac { \text g } { \text { mol } } $ , to convert from moles to grams of $ \text { nacl } $ : $ \text { mass of nacl } =0.200\ , \cancel { \text { mol } } \times \dfrac { 58.44\ , \text g } { 1\ , \cancel { \text { mol } } } = 11.7\ , \text { g nacl } $ in practice , we could use this information to make our solution as follows : step $ 1.~ $ weigh out $ 11.7\ , \text g $ of sodium chloride . step $ 2.~ $ transfer the sodium chloride to a clean , dry flask . step $ 3.~ $ add water to the $ \text { nacl } $ until the total volume of the solution is $ 250\ , \text { ml } $ . step $ 4.~ $ stir until the $ \text { nacl } $ is completely dissolved . the accuracy of our molar concentration depends on our choice of glassware , as well as the accuracy of the balance we use to measure out the solute . the glassware determines the accuracy of our solution volume . if we are n't being too picky , we might mix the solution in a erlenmeyer flask or beaker . if we want to extremely precise , such as when making a standard solution for an analytical chemistry experiment , we would probably mix the solute and solvent in a volumetric flask ( see picture below ) . summary mixtures with uniform composition are called homogeneous solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . try it : the stoichiometry of a precipitation reaction molarity is a useful concept for stoichiometric calculations involving reactions in solution , such precipitation and neutralization reactions . for example , consider the precipitation reaction that occurs between $ \text { pb ( no } _3 ) _2 ( aq ) $ and $ \text { ki } ( aq ) $ . when these two solutions are combined , bright yellow $ \text { pbi } _2 ( s ) $ precipitates out of solution . the balanced equation for this reaction is : $ \text { pb ( no } _3 ) _2 ( aq ) + 2\text { ki } ( aq ) \rightarrow \text { pbi } _2 ( s ) + 2\text { kno } _3 ( aq ) $ if we have $ 0.1\ , \text { l } $ of $ 0.10\ , \text { m pb ( no } _3 ) _2 $ , what volume of $ 0.10\ , \text { m ki } ( aq ) $ should we add to react with all the $ \text { pb ( no } _3 ) _2 ( aq ) $ ?
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example 1 : calculating the molar concentration of a solute let 's consider a solution made by dissolving $ 2.355\ , \text g $ of sulfuric acid , $ \text h_2 \text { so } _4 $ , in water . the total volume of the solution is $ 50.0\ , \text { ml } $ . what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ?
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if the density of said solution is 1.02g/ml , what is our percent by mass of barium iodide ?
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key points mixtures with uniform composition are called homogeneous mixtures or solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . introduction : mixtures and solutions in real life , we often encounter substances that are mixtures of different elements and compounds . one example of a mixture is the human body . did you know that the human body is approximately $ 57\ % $ water by mass ? we are basically an assortment of biological molecules , gases , and inorganic ions dissolved in water . i do n't know about you , but i find that pretty mind-boggling ! if substances are mixed together in such a way that the composition is the same throughout the sample , they are called homogeneous mixtures . in contrast , a mixture that does not have a uniform composition throughout the sample is called heterogeneous . homogeneous mixtures are also known as solutions , and solutions can contain components that are solids , liquids and/or gases . we often want to be able to quantify the amount of a species that is in the solution , which is called the concentration of that species . in this article , we 'll look at how to describe solutions quantitatively , and discuss how that information can be used when doing stoichiometric calculations . molar concentration the component of a solution that is present in the largest amount is known as the solvent . any chemical species mixed in the solvent is called a solute , and solutes can be gases , liquids , or solids . for example , earth 's atmosphere is a mixture of $ 78\ % $ nitrogen gas , $ 21\ % $ oxygen gas , and $ 1\ % $ argon , carbon dioxide , and other gases . we can think of the atmosphere as a solution where nitrogen gas is the solvent , and the solutes are oxygen , argon and carbon dioxide . the molarity or molar concentration of a solute is defined as the number of moles of solute per liter of solution ( not per liter of solvent ! ) : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molarity has units of $ \dfrac { \text { mol } } { \text { liter } } $ , which can be abbreviated as molar or $ \text m $ ( pronounced `` molar '' ) . the molar concentration of the solute is sometimes abbreviated by putting square brackets around the chemical formula of the solute . for example , the concentration of chloride ions in a solution can be written as $ [ \text { cl } ^- ] $ . molar concentration allows us to convert between the volume of the solution and the moles ( or mass ) of the solute . concept check : bronze is an alloy that can be thought of as a solid solution of ~ $ 88\ % $ copper mixed with $ 12\ % $ tin . what is the solute and solvent in bronze ? example 1 : calculating the molar concentration of a solute let 's consider a solution made by dissolving $ 2.355\ , \text g $ of sulfuric acid , $ \text h_2 \text { so } _4 $ , in water . the total volume of the solution is $ 50.0\ , \text { ml } $ . what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ? to find $ [ \text h_2 \text { so } _4 ] $ we need to find out how many moles of sulfuric acid are in solution . we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ? example 2 : making a solution with a specific concentration sometimes we have a desired concentration and volume of solution , and we want to know how much solute we need to make the solution . in that case , we can rearrange the molarity equation to solve for the moles of solute . $ \text { mol solute } = { \text { molarity } } \times { \text { l of solution } } $ for example , let 's say we want to make $ 0.250\ , \text { l } $ of an aqueous solution with $ [ \text { nacl } ] =0.800\ , \text { m } $ . what mass of the solute , $ \text { nacl } $ , would we need to make this solution ? we can use the rearranged molarity equation to calculate the moles of $ \text { nacl } $ needed for the specified concentration and volume : $ \begin { align } \text { mol nacl } & amp ; = [ \text { nacl } ] \times { \text { l of solution } } \ & amp ; =0.800\ , \dfrac { \text { mol } } { \cancel { \text l } } \times 0.250\ , \cancel { \text { l } } \ & amp ; =0.200\ , \text { mol nacl } \end { align } $ we can then use the molecular weight of sodium chloride , $ 58.44\ , \dfrac { \text g } { \text { mol } } $ , to convert from moles to grams of $ \text { nacl } $ : $ \text { mass of nacl } =0.200\ , \cancel { \text { mol } } \times \dfrac { 58.44\ , \text g } { 1\ , \cancel { \text { mol } } } = 11.7\ , \text { g nacl } $ in practice , we could use this information to make our solution as follows : step $ 1.~ $ weigh out $ 11.7\ , \text g $ of sodium chloride . step $ 2.~ $ transfer the sodium chloride to a clean , dry flask . step $ 3.~ $ add water to the $ \text { nacl } $ until the total volume of the solution is $ 250\ , \text { ml } $ . step $ 4.~ $ stir until the $ \text { nacl } $ is completely dissolved . the accuracy of our molar concentration depends on our choice of glassware , as well as the accuracy of the balance we use to measure out the solute . the glassware determines the accuracy of our solution volume . if we are n't being too picky , we might mix the solution in a erlenmeyer flask or beaker . if we want to extremely precise , such as when making a standard solution for an analytical chemistry experiment , we would probably mix the solute and solvent in a volumetric flask ( see picture below ) . summary mixtures with uniform composition are called homogeneous solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . try it : the stoichiometry of a precipitation reaction molarity is a useful concept for stoichiometric calculations involving reactions in solution , such precipitation and neutralization reactions . for example , consider the precipitation reaction that occurs between $ \text { pb ( no } _3 ) _2 ( aq ) $ and $ \text { ki } ( aq ) $ . when these two solutions are combined , bright yellow $ \text { pbi } _2 ( s ) $ precipitates out of solution . the balanced equation for this reaction is : $ \text { pb ( no } _3 ) _2 ( aq ) + 2\text { ki } ( aq ) \rightarrow \text { pbi } _2 ( s ) + 2\text { kno } _3 ( aq ) $ if we have $ 0.1\ , \text { l } $ of $ 0.10\ , \text { m pb ( no } _3 ) _2 $ , what volume of $ 0.10\ , \text { m ki } ( aq ) $ should we add to react with all the $ \text { pb ( no } _3 ) _2 ( aq ) $ ?
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for example , the concentration of chloride ions in a solution can be written as $ [ \text { cl } ^- ] $ . molar concentration allows us to convert between the volume of the solution and the moles ( or mass ) of the solute . concept check : bronze is an alloy that can be thought of as a solid solution of ~ $ 88\ % $ copper mixed with $ 12\ % $ tin .
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is molecular weight the same thing as molar mass ?
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key points mixtures with uniform composition are called homogeneous mixtures or solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . introduction : mixtures and solutions in real life , we often encounter substances that are mixtures of different elements and compounds . one example of a mixture is the human body . did you know that the human body is approximately $ 57\ % $ water by mass ? we are basically an assortment of biological molecules , gases , and inorganic ions dissolved in water . i do n't know about you , but i find that pretty mind-boggling ! if substances are mixed together in such a way that the composition is the same throughout the sample , they are called homogeneous mixtures . in contrast , a mixture that does not have a uniform composition throughout the sample is called heterogeneous . homogeneous mixtures are also known as solutions , and solutions can contain components that are solids , liquids and/or gases . we often want to be able to quantify the amount of a species that is in the solution , which is called the concentration of that species . in this article , we 'll look at how to describe solutions quantitatively , and discuss how that information can be used when doing stoichiometric calculations . molar concentration the component of a solution that is present in the largest amount is known as the solvent . any chemical species mixed in the solvent is called a solute , and solutes can be gases , liquids , or solids . for example , earth 's atmosphere is a mixture of $ 78\ % $ nitrogen gas , $ 21\ % $ oxygen gas , and $ 1\ % $ argon , carbon dioxide , and other gases . we can think of the atmosphere as a solution where nitrogen gas is the solvent , and the solutes are oxygen , argon and carbon dioxide . the molarity or molar concentration of a solute is defined as the number of moles of solute per liter of solution ( not per liter of solvent ! ) : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molarity has units of $ \dfrac { \text { mol } } { \text { liter } } $ , which can be abbreviated as molar or $ \text m $ ( pronounced `` molar '' ) . the molar concentration of the solute is sometimes abbreviated by putting square brackets around the chemical formula of the solute . for example , the concentration of chloride ions in a solution can be written as $ [ \text { cl } ^- ] $ . molar concentration allows us to convert between the volume of the solution and the moles ( or mass ) of the solute . concept check : bronze is an alloy that can be thought of as a solid solution of ~ $ 88\ % $ copper mixed with $ 12\ % $ tin . what is the solute and solvent in bronze ? example 1 : calculating the molar concentration of a solute let 's consider a solution made by dissolving $ 2.355\ , \text g $ of sulfuric acid , $ \text h_2 \text { so } _4 $ , in water . the total volume of the solution is $ 50.0\ , \text { ml } $ . what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ? to find $ [ \text h_2 \text { so } _4 ] $ we need to find out how many moles of sulfuric acid are in solution . we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ? example 2 : making a solution with a specific concentration sometimes we have a desired concentration and volume of solution , and we want to know how much solute we need to make the solution . in that case , we can rearrange the molarity equation to solve for the moles of solute . $ \text { mol solute } = { \text { molarity } } \times { \text { l of solution } } $ for example , let 's say we want to make $ 0.250\ , \text { l } $ of an aqueous solution with $ [ \text { nacl } ] =0.800\ , \text { m } $ . what mass of the solute , $ \text { nacl } $ , would we need to make this solution ? we can use the rearranged molarity equation to calculate the moles of $ \text { nacl } $ needed for the specified concentration and volume : $ \begin { align } \text { mol nacl } & amp ; = [ \text { nacl } ] \times { \text { l of solution } } \ & amp ; =0.800\ , \dfrac { \text { mol } } { \cancel { \text l } } \times 0.250\ , \cancel { \text { l } } \ & amp ; =0.200\ , \text { mol nacl } \end { align } $ we can then use the molecular weight of sodium chloride , $ 58.44\ , \dfrac { \text g } { \text { mol } } $ , to convert from moles to grams of $ \text { nacl } $ : $ \text { mass of nacl } =0.200\ , \cancel { \text { mol } } \times \dfrac { 58.44\ , \text g } { 1\ , \cancel { \text { mol } } } = 11.7\ , \text { g nacl } $ in practice , we could use this information to make our solution as follows : step $ 1.~ $ weigh out $ 11.7\ , \text g $ of sodium chloride . step $ 2.~ $ transfer the sodium chloride to a clean , dry flask . step $ 3.~ $ add water to the $ \text { nacl } $ until the total volume of the solution is $ 250\ , \text { ml } $ . step $ 4.~ $ stir until the $ \text { nacl } $ is completely dissolved . the accuracy of our molar concentration depends on our choice of glassware , as well as the accuracy of the balance we use to measure out the solute . the glassware determines the accuracy of our solution volume . if we are n't being too picky , we might mix the solution in a erlenmeyer flask or beaker . if we want to extremely precise , such as when making a standard solution for an analytical chemistry experiment , we would probably mix the solute and solvent in a volumetric flask ( see picture below ) . summary mixtures with uniform composition are called homogeneous solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . try it : the stoichiometry of a precipitation reaction molarity is a useful concept for stoichiometric calculations involving reactions in solution , such precipitation and neutralization reactions . for example , consider the precipitation reaction that occurs between $ \text { pb ( no } _3 ) _2 ( aq ) $ and $ \text { ki } ( aq ) $ . when these two solutions are combined , bright yellow $ \text { pbi } _2 ( s ) $ precipitates out of solution . the balanced equation for this reaction is : $ \text { pb ( no } _3 ) _2 ( aq ) + 2\text { ki } ( aq ) \rightarrow \text { pbi } _2 ( s ) + 2\text { kno } _3 ( aq ) $ if we have $ 0.1\ , \text { l } $ of $ 0.10\ , \text { m pb ( no } _3 ) _2 $ , what volume of $ 0.10\ , \text { m ki } ( aq ) $ should we add to react with all the $ \text { pb ( no } _3 ) _2 ( aq ) $ ?
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in that case , we can rearrange the molarity equation to solve for the moles of solute . $ \text { mol solute } = { \text { molarity } } \times { \text { l of solution } } $ for example , let 's say we want to make $ 0.250\ , \text { l } $ of an aqueous solution with $ [ \text { nacl } ] =0.800\ , \text { m } $ . what mass of the solute , $ \text { nacl } $ , would we need to make this solution ?
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in a problem like the one with the 0.250 l of an aqueous solution and 0.800 m , what if you were given ml ?
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key points mixtures with uniform composition are called homogeneous mixtures or solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . introduction : mixtures and solutions in real life , we often encounter substances that are mixtures of different elements and compounds . one example of a mixture is the human body . did you know that the human body is approximately $ 57\ % $ water by mass ? we are basically an assortment of biological molecules , gases , and inorganic ions dissolved in water . i do n't know about you , but i find that pretty mind-boggling ! if substances are mixed together in such a way that the composition is the same throughout the sample , they are called homogeneous mixtures . in contrast , a mixture that does not have a uniform composition throughout the sample is called heterogeneous . homogeneous mixtures are also known as solutions , and solutions can contain components that are solids , liquids and/or gases . we often want to be able to quantify the amount of a species that is in the solution , which is called the concentration of that species . in this article , we 'll look at how to describe solutions quantitatively , and discuss how that information can be used when doing stoichiometric calculations . molar concentration the component of a solution that is present in the largest amount is known as the solvent . any chemical species mixed in the solvent is called a solute , and solutes can be gases , liquids , or solids . for example , earth 's atmosphere is a mixture of $ 78\ % $ nitrogen gas , $ 21\ % $ oxygen gas , and $ 1\ % $ argon , carbon dioxide , and other gases . we can think of the atmosphere as a solution where nitrogen gas is the solvent , and the solutes are oxygen , argon and carbon dioxide . the molarity or molar concentration of a solute is defined as the number of moles of solute per liter of solution ( not per liter of solvent ! ) : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molarity has units of $ \dfrac { \text { mol } } { \text { liter } } $ , which can be abbreviated as molar or $ \text m $ ( pronounced `` molar '' ) . the molar concentration of the solute is sometimes abbreviated by putting square brackets around the chemical formula of the solute . for example , the concentration of chloride ions in a solution can be written as $ [ \text { cl } ^- ] $ . molar concentration allows us to convert between the volume of the solution and the moles ( or mass ) of the solute . concept check : bronze is an alloy that can be thought of as a solid solution of ~ $ 88\ % $ copper mixed with $ 12\ % $ tin . what is the solute and solvent in bronze ? example 1 : calculating the molar concentration of a solute let 's consider a solution made by dissolving $ 2.355\ , \text g $ of sulfuric acid , $ \text h_2 \text { so } _4 $ , in water . the total volume of the solution is $ 50.0\ , \text { ml } $ . what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ? to find $ [ \text h_2 \text { so } _4 ] $ we need to find out how many moles of sulfuric acid are in solution . we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ? example 2 : making a solution with a specific concentration sometimes we have a desired concentration and volume of solution , and we want to know how much solute we need to make the solution . in that case , we can rearrange the molarity equation to solve for the moles of solute . $ \text { mol solute } = { \text { molarity } } \times { \text { l of solution } } $ for example , let 's say we want to make $ 0.250\ , \text { l } $ of an aqueous solution with $ [ \text { nacl } ] =0.800\ , \text { m } $ . what mass of the solute , $ \text { nacl } $ , would we need to make this solution ? we can use the rearranged molarity equation to calculate the moles of $ \text { nacl } $ needed for the specified concentration and volume : $ \begin { align } \text { mol nacl } & amp ; = [ \text { nacl } ] \times { \text { l of solution } } \ & amp ; =0.800\ , \dfrac { \text { mol } } { \cancel { \text l } } \times 0.250\ , \cancel { \text { l } } \ & amp ; =0.200\ , \text { mol nacl } \end { align } $ we can then use the molecular weight of sodium chloride , $ 58.44\ , \dfrac { \text g } { \text { mol } } $ , to convert from moles to grams of $ \text { nacl } $ : $ \text { mass of nacl } =0.200\ , \cancel { \text { mol } } \times \dfrac { 58.44\ , \text g } { 1\ , \cancel { \text { mol } } } = 11.7\ , \text { g nacl } $ in practice , we could use this information to make our solution as follows : step $ 1.~ $ weigh out $ 11.7\ , \text g $ of sodium chloride . step $ 2.~ $ transfer the sodium chloride to a clean , dry flask . step $ 3.~ $ add water to the $ \text { nacl } $ until the total volume of the solution is $ 250\ , \text { ml } $ . step $ 4.~ $ stir until the $ \text { nacl } $ is completely dissolved . the accuracy of our molar concentration depends on our choice of glassware , as well as the accuracy of the balance we use to measure out the solute . the glassware determines the accuracy of our solution volume . if we are n't being too picky , we might mix the solution in a erlenmeyer flask or beaker . if we want to extremely precise , such as when making a standard solution for an analytical chemistry experiment , we would probably mix the solute and solvent in a volumetric flask ( see picture below ) . summary mixtures with uniform composition are called homogeneous solutions . mixtures with non-uniform composition are heterogeneous mixtures . the chemical in the mixture that is present in the largest amount is called the solvent , and the other components are called solutes . molarity or molar concentration is the number of moles of solute per liter of solution , which can be calculated using the following equation : $ \text { molarity } = \dfrac { \text { mol solute } } { \text { l of solution } } $ molar concentration can be used to convert between the mass or moles of solute and the volume of the solution . try it : the stoichiometry of a precipitation reaction molarity is a useful concept for stoichiometric calculations involving reactions in solution , such precipitation and neutralization reactions . for example , consider the precipitation reaction that occurs between $ \text { pb ( no } _3 ) _2 ( aq ) $ and $ \text { ki } ( aq ) $ . when these two solutions are combined , bright yellow $ \text { pbi } _2 ( s ) $ precipitates out of solution . the balanced equation for this reaction is : $ \text { pb ( no } _3 ) _2 ( aq ) + 2\text { ki } ( aq ) \rightarrow \text { pbi } _2 ( s ) + 2\text { kno } _3 ( aq ) $ if we have $ 0.1\ , \text { l } $ of $ 0.10\ , \text { m pb ( no } _3 ) _2 $ , what volume of $ 0.10\ , \text { m ki } ( aq ) $ should we add to react with all the $ \text { pb ( no } _3 ) _2 ( aq ) $ ?
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what is the molar concentration of sulfuric acid , $ [ \text h_2 \text { so } _4 ] $ ? to find $ [ \text h_2 \text { so } _4 ] $ we need to find out how many moles of sulfuric acid are in solution . we can convert the mass of the solute to moles using the molecular weight of sulfuric acid , $ 98.08\ , \dfrac { \text g } { \text { mol } } $ : $ \text { mol h } _2\text { so } _4=2.355\ , \cancel { \text { g h } _2\text { so } _4 } \times \dfrac { 1\ , \text { mol } } { 98.08\ , \cancel { \text { g } } } = 0.02401\ , \text { mol h } _2\text { so } _4 $ we can now plug in the moles of sulfuric acid and total volume of solution in the molarity equation to calculate the molar concentration of sulfuric acid : $ \begin { align } [ \text h_2 \text { so } _4 ] & amp ; = \dfrac { \text { mol solute } } { \text { l of solution } } \ \ & amp ; =\dfrac { 0.02401\ , \text { mol } } { 0.050\ , \text l } \ \ & amp ; =.48 \ , \text m\end { align } $ concept check : what is the molar concentration of $ \text h^+ $ ions in our $ 4.8\ , \text { m h } _2 \text { so } _4 $ solution ?
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how many grams of k2cro4 are needed ?
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some mountains are made of solid rock , like the rocky mountains or the swiss alps . but , some mountains are actually volcanoes . volcanoes are vents , or openings in the earth 's crust , that release ash , gases and steam , and hot liquid rock called lava . when the lava cools and hardens , it forms into the cone‐shaped mountain we think of as a volcano . most of the world 's volcanoes are found around the edges of tectonic plates , both on land and in the oceans . on land , volcanoes form when one tectonic plate moves under another . usually a thin , heavy oceanic plate subducts , or moves under , a thicker continental plate . when this happens , the ocean plate sinks into the mantle . water trapped in the rocks in this plate gets squeezed out . this causes some of the rocks to melt . the melted rock , or magma , is lighter than the surrounding rock and rises up . this magma collects in magma chambers , but it is still miles below the surface . when enough magma builds up in the magma chamber , it forces its way up to the surface and erupts , often causing volcanic eruptions . in the ocean , volcanoes erupt along cracks that are opened in the ocean floor by the spreading of two plates called a mid‐ocean ridge . magma from the earth 's upper mantle rises up to fill these cracks . as the lava cools , it forms new crust on the edges of the cracks . these mid‐ocean ridges are actually long chains of underwater volcanoes that circle the earth like the seams on a baseball . about 80 to 90 percent of all volcanic eruptions occur where the plates spread apart . hot spots some volcanoes pop up in random places , often far from the edge of a tectonic plate . these volcanoes are found over `` hot spots . '' a hot spot is an intensely hot area in the mantle below the earth 's crust . the heat that fuels the hot spot comes from very deep in the earth . this heat causes the mantle in that region to melt . the molten magma rises up and breaks through the crust to form a volcano . while the hot spot stays in one place , rooted to its deep source of heat , the tectonic plate is slowly moving above it . as the plate moves , so does the volcano , and another one forms in its place . the volcano that moved is no longer active . this is why a chain of extinct volcanoes is often found extending from a hot spot . hot spots are found around the globe , on land and in the ocean . the hawaiian islands are the youngest volcanic mountains in a long chain of volcanoes that formed over a hotspot . they are still forming today . another hot spot is under yellowstone national park , where the heat causes boiling mud pools and geysers like old faithful .
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hot spots some volcanoes pop up in random places , often far from the edge of a tectonic plate . these volcanoes are found over `` hot spots . '' a hot spot is an intensely hot area in the mantle below the earth 's crust . the heat that fuels the hot spot comes from very deep in the earth .
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does the land have to move in order to be a hot spot ?
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some mountains are made of solid rock , like the rocky mountains or the swiss alps . but , some mountains are actually volcanoes . volcanoes are vents , or openings in the earth 's crust , that release ash , gases and steam , and hot liquid rock called lava . when the lava cools and hardens , it forms into the cone‐shaped mountain we think of as a volcano . most of the world 's volcanoes are found around the edges of tectonic plates , both on land and in the oceans . on land , volcanoes form when one tectonic plate moves under another . usually a thin , heavy oceanic plate subducts , or moves under , a thicker continental plate . when this happens , the ocean plate sinks into the mantle . water trapped in the rocks in this plate gets squeezed out . this causes some of the rocks to melt . the melted rock , or magma , is lighter than the surrounding rock and rises up . this magma collects in magma chambers , but it is still miles below the surface . when enough magma builds up in the magma chamber , it forces its way up to the surface and erupts , often causing volcanic eruptions . in the ocean , volcanoes erupt along cracks that are opened in the ocean floor by the spreading of two plates called a mid‐ocean ridge . magma from the earth 's upper mantle rises up to fill these cracks . as the lava cools , it forms new crust on the edges of the cracks . these mid‐ocean ridges are actually long chains of underwater volcanoes that circle the earth like the seams on a baseball . about 80 to 90 percent of all volcanic eruptions occur where the plates spread apart . hot spots some volcanoes pop up in random places , often far from the edge of a tectonic plate . these volcanoes are found over `` hot spots . '' a hot spot is an intensely hot area in the mantle below the earth 's crust . the heat that fuels the hot spot comes from very deep in the earth . this heat causes the mantle in that region to melt . the molten magma rises up and breaks through the crust to form a volcano . while the hot spot stays in one place , rooted to its deep source of heat , the tectonic plate is slowly moving above it . as the plate moves , so does the volcano , and another one forms in its place . the volcano that moved is no longer active . this is why a chain of extinct volcanoes is often found extending from a hot spot . hot spots are found around the globe , on land and in the ocean . the hawaiian islands are the youngest volcanic mountains in a long chain of volcanoes that formed over a hotspot . they are still forming today . another hot spot is under yellowstone national park , where the heat causes boiling mud pools and geysers like old faithful .
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most of the world 's volcanoes are found around the edges of tectonic plates , both on land and in the oceans . on land , volcanoes form when one tectonic plate moves under another . usually a thin , heavy oceanic plate subducts , or moves under , a thicker continental plate .
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how can yellow stone still be active if the tectonic plate is moving ?
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some mountains are made of solid rock , like the rocky mountains or the swiss alps . but , some mountains are actually volcanoes . volcanoes are vents , or openings in the earth 's crust , that release ash , gases and steam , and hot liquid rock called lava . when the lava cools and hardens , it forms into the cone‐shaped mountain we think of as a volcano . most of the world 's volcanoes are found around the edges of tectonic plates , both on land and in the oceans . on land , volcanoes form when one tectonic plate moves under another . usually a thin , heavy oceanic plate subducts , or moves under , a thicker continental plate . when this happens , the ocean plate sinks into the mantle . water trapped in the rocks in this plate gets squeezed out . this causes some of the rocks to melt . the melted rock , or magma , is lighter than the surrounding rock and rises up . this magma collects in magma chambers , but it is still miles below the surface . when enough magma builds up in the magma chamber , it forces its way up to the surface and erupts , often causing volcanic eruptions . in the ocean , volcanoes erupt along cracks that are opened in the ocean floor by the spreading of two plates called a mid‐ocean ridge . magma from the earth 's upper mantle rises up to fill these cracks . as the lava cools , it forms new crust on the edges of the cracks . these mid‐ocean ridges are actually long chains of underwater volcanoes that circle the earth like the seams on a baseball . about 80 to 90 percent of all volcanic eruptions occur where the plates spread apart . hot spots some volcanoes pop up in random places , often far from the edge of a tectonic plate . these volcanoes are found over `` hot spots . '' a hot spot is an intensely hot area in the mantle below the earth 's crust . the heat that fuels the hot spot comes from very deep in the earth . this heat causes the mantle in that region to melt . the molten magma rises up and breaks through the crust to form a volcano . while the hot spot stays in one place , rooted to its deep source of heat , the tectonic plate is slowly moving above it . as the plate moves , so does the volcano , and another one forms in its place . the volcano that moved is no longer active . this is why a chain of extinct volcanoes is often found extending from a hot spot . hot spots are found around the globe , on land and in the ocean . the hawaiian islands are the youngest volcanic mountains in a long chain of volcanoes that formed over a hotspot . they are still forming today . another hot spot is under yellowstone national park , where the heat causes boiling mud pools and geysers like old faithful .
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while the hot spot stays in one place , rooted to its deep source of heat , the tectonic plate is slowly moving above it . as the plate moves , so does the volcano , and another one forms in its place . the volcano that moved is no longer active . this is why a chain of extinct volcanoes is often found extending from a hot spot .
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is the volcano under the ocean floor can have a possibility to explode like the youngest volcano in land ?
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some mountains are made of solid rock , like the rocky mountains or the swiss alps . but , some mountains are actually volcanoes . volcanoes are vents , or openings in the earth 's crust , that release ash , gases and steam , and hot liquid rock called lava . when the lava cools and hardens , it forms into the cone‐shaped mountain we think of as a volcano . most of the world 's volcanoes are found around the edges of tectonic plates , both on land and in the oceans . on land , volcanoes form when one tectonic plate moves under another . usually a thin , heavy oceanic plate subducts , or moves under , a thicker continental plate . when this happens , the ocean plate sinks into the mantle . water trapped in the rocks in this plate gets squeezed out . this causes some of the rocks to melt . the melted rock , or magma , is lighter than the surrounding rock and rises up . this magma collects in magma chambers , but it is still miles below the surface . when enough magma builds up in the magma chamber , it forces its way up to the surface and erupts , often causing volcanic eruptions . in the ocean , volcanoes erupt along cracks that are opened in the ocean floor by the spreading of two plates called a mid‐ocean ridge . magma from the earth 's upper mantle rises up to fill these cracks . as the lava cools , it forms new crust on the edges of the cracks . these mid‐ocean ridges are actually long chains of underwater volcanoes that circle the earth like the seams on a baseball . about 80 to 90 percent of all volcanic eruptions occur where the plates spread apart . hot spots some volcanoes pop up in random places , often far from the edge of a tectonic plate . these volcanoes are found over `` hot spots . '' a hot spot is an intensely hot area in the mantle below the earth 's crust . the heat that fuels the hot spot comes from very deep in the earth . this heat causes the mantle in that region to melt . the molten magma rises up and breaks through the crust to form a volcano . while the hot spot stays in one place , rooted to its deep source of heat , the tectonic plate is slowly moving above it . as the plate moves , so does the volcano , and another one forms in its place . the volcano that moved is no longer active . this is why a chain of extinct volcanoes is often found extending from a hot spot . hot spots are found around the globe , on land and in the ocean . the hawaiian islands are the youngest volcanic mountains in a long chain of volcanoes that formed over a hotspot . they are still forming today . another hot spot is under yellowstone national park , where the heat causes boiling mud pools and geysers like old faithful .
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as the plate moves , so does the volcano , and another one forms in its place . the volcano that moved is no longer active . this is why a chain of extinct volcanoes is often found extending from a hot spot .
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is mount st. helens the most active volcano on the face of planet earth ?
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some mountains are made of solid rock , like the rocky mountains or the swiss alps . but , some mountains are actually volcanoes . volcanoes are vents , or openings in the earth 's crust , that release ash , gases and steam , and hot liquid rock called lava . when the lava cools and hardens , it forms into the cone‐shaped mountain we think of as a volcano . most of the world 's volcanoes are found around the edges of tectonic plates , both on land and in the oceans . on land , volcanoes form when one tectonic plate moves under another . usually a thin , heavy oceanic plate subducts , or moves under , a thicker continental plate . when this happens , the ocean plate sinks into the mantle . water trapped in the rocks in this plate gets squeezed out . this causes some of the rocks to melt . the melted rock , or magma , is lighter than the surrounding rock and rises up . this magma collects in magma chambers , but it is still miles below the surface . when enough magma builds up in the magma chamber , it forces its way up to the surface and erupts , often causing volcanic eruptions . in the ocean , volcanoes erupt along cracks that are opened in the ocean floor by the spreading of two plates called a mid‐ocean ridge . magma from the earth 's upper mantle rises up to fill these cracks . as the lava cools , it forms new crust on the edges of the cracks . these mid‐ocean ridges are actually long chains of underwater volcanoes that circle the earth like the seams on a baseball . about 80 to 90 percent of all volcanic eruptions occur where the plates spread apart . hot spots some volcanoes pop up in random places , often far from the edge of a tectonic plate . these volcanoes are found over `` hot spots . '' a hot spot is an intensely hot area in the mantle below the earth 's crust . the heat that fuels the hot spot comes from very deep in the earth . this heat causes the mantle in that region to melt . the molten magma rises up and breaks through the crust to form a volcano . while the hot spot stays in one place , rooted to its deep source of heat , the tectonic plate is slowly moving above it . as the plate moves , so does the volcano , and another one forms in its place . the volcano that moved is no longer active . this is why a chain of extinct volcanoes is often found extending from a hot spot . hot spots are found around the globe , on land and in the ocean . the hawaiian islands are the youngest volcanic mountains in a long chain of volcanoes that formed over a hotspot . they are still forming today . another hot spot is under yellowstone national park , where the heat causes boiling mud pools and geysers like old faithful .
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as the plate moves , so does the volcano , and another one forms in its place . the volcano that moved is no longer active . this is why a chain of extinct volcanoes is often found extending from a hot spot .
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why might geologists still consider mount jefferson to be an active volcano ?
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some mountains are made of solid rock , like the rocky mountains or the swiss alps . but , some mountains are actually volcanoes . volcanoes are vents , or openings in the earth 's crust , that release ash , gases and steam , and hot liquid rock called lava . when the lava cools and hardens , it forms into the cone‐shaped mountain we think of as a volcano . most of the world 's volcanoes are found around the edges of tectonic plates , both on land and in the oceans . on land , volcanoes form when one tectonic plate moves under another . usually a thin , heavy oceanic plate subducts , or moves under , a thicker continental plate . when this happens , the ocean plate sinks into the mantle . water trapped in the rocks in this plate gets squeezed out . this causes some of the rocks to melt . the melted rock , or magma , is lighter than the surrounding rock and rises up . this magma collects in magma chambers , but it is still miles below the surface . when enough magma builds up in the magma chamber , it forces its way up to the surface and erupts , often causing volcanic eruptions . in the ocean , volcanoes erupt along cracks that are opened in the ocean floor by the spreading of two plates called a mid‐ocean ridge . magma from the earth 's upper mantle rises up to fill these cracks . as the lava cools , it forms new crust on the edges of the cracks . these mid‐ocean ridges are actually long chains of underwater volcanoes that circle the earth like the seams on a baseball . about 80 to 90 percent of all volcanic eruptions occur where the plates spread apart . hot spots some volcanoes pop up in random places , often far from the edge of a tectonic plate . these volcanoes are found over `` hot spots . '' a hot spot is an intensely hot area in the mantle below the earth 's crust . the heat that fuels the hot spot comes from very deep in the earth . this heat causes the mantle in that region to melt . the molten magma rises up and breaks through the crust to form a volcano . while the hot spot stays in one place , rooted to its deep source of heat , the tectonic plate is slowly moving above it . as the plate moves , so does the volcano , and another one forms in its place . the volcano that moved is no longer active . this is why a chain of extinct volcanoes is often found extending from a hot spot . hot spots are found around the globe , on land and in the ocean . the hawaiian islands are the youngest volcanic mountains in a long chain of volcanoes that formed over a hotspot . they are still forming today . another hot spot is under yellowstone national park , where the heat causes boiling mud pools and geysers like old faithful .
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some mountains are made of solid rock , like the rocky mountains or the swiss alps . but , some mountains are actually volcanoes . volcanoes are vents , or openings in the earth 's crust , that release ash , gases and steam , and hot liquid rock called lava .
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why do we have volcanoes for ?
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some mountains are made of solid rock , like the rocky mountains or the swiss alps . but , some mountains are actually volcanoes . volcanoes are vents , or openings in the earth 's crust , that release ash , gases and steam , and hot liquid rock called lava . when the lava cools and hardens , it forms into the cone‐shaped mountain we think of as a volcano . most of the world 's volcanoes are found around the edges of tectonic plates , both on land and in the oceans . on land , volcanoes form when one tectonic plate moves under another . usually a thin , heavy oceanic plate subducts , or moves under , a thicker continental plate . when this happens , the ocean plate sinks into the mantle . water trapped in the rocks in this plate gets squeezed out . this causes some of the rocks to melt . the melted rock , or magma , is lighter than the surrounding rock and rises up . this magma collects in magma chambers , but it is still miles below the surface . when enough magma builds up in the magma chamber , it forces its way up to the surface and erupts , often causing volcanic eruptions . in the ocean , volcanoes erupt along cracks that are opened in the ocean floor by the spreading of two plates called a mid‐ocean ridge . magma from the earth 's upper mantle rises up to fill these cracks . as the lava cools , it forms new crust on the edges of the cracks . these mid‐ocean ridges are actually long chains of underwater volcanoes that circle the earth like the seams on a baseball . about 80 to 90 percent of all volcanic eruptions occur where the plates spread apart . hot spots some volcanoes pop up in random places , often far from the edge of a tectonic plate . these volcanoes are found over `` hot spots . '' a hot spot is an intensely hot area in the mantle below the earth 's crust . the heat that fuels the hot spot comes from very deep in the earth . this heat causes the mantle in that region to melt . the molten magma rises up and breaks through the crust to form a volcano . while the hot spot stays in one place , rooted to its deep source of heat , the tectonic plate is slowly moving above it . as the plate moves , so does the volcano , and another one forms in its place . the volcano that moved is no longer active . this is why a chain of extinct volcanoes is often found extending from a hot spot . hot spots are found around the globe , on land and in the ocean . the hawaiian islands are the youngest volcanic mountains in a long chain of volcanoes that formed over a hotspot . they are still forming today . another hot spot is under yellowstone national park , where the heat causes boiling mud pools and geysers like old faithful .
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the melted rock , or magma , is lighter than the surrounding rock and rises up . this magma collects in magma chambers , but it is still miles below the surface . when enough magma builds up in the magma chamber , it forces its way up to the surface and erupts , often causing volcanic eruptions . in the ocean , volcanoes erupt along cracks that are opened in the ocean floor by the spreading of two plates called a mid‐ocean ridge .
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how does the magma have enough force to break the crust and shoot 3-4 metres up in the air ?
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some mountains are made of solid rock , like the rocky mountains or the swiss alps . but , some mountains are actually volcanoes . volcanoes are vents , or openings in the earth 's crust , that release ash , gases and steam , and hot liquid rock called lava . when the lava cools and hardens , it forms into the cone‐shaped mountain we think of as a volcano . most of the world 's volcanoes are found around the edges of tectonic plates , both on land and in the oceans . on land , volcanoes form when one tectonic plate moves under another . usually a thin , heavy oceanic plate subducts , or moves under , a thicker continental plate . when this happens , the ocean plate sinks into the mantle . water trapped in the rocks in this plate gets squeezed out . this causes some of the rocks to melt . the melted rock , or magma , is lighter than the surrounding rock and rises up . this magma collects in magma chambers , but it is still miles below the surface . when enough magma builds up in the magma chamber , it forces its way up to the surface and erupts , often causing volcanic eruptions . in the ocean , volcanoes erupt along cracks that are opened in the ocean floor by the spreading of two plates called a mid‐ocean ridge . magma from the earth 's upper mantle rises up to fill these cracks . as the lava cools , it forms new crust on the edges of the cracks . these mid‐ocean ridges are actually long chains of underwater volcanoes that circle the earth like the seams on a baseball . about 80 to 90 percent of all volcanic eruptions occur where the plates spread apart . hot spots some volcanoes pop up in random places , often far from the edge of a tectonic plate . these volcanoes are found over `` hot spots . '' a hot spot is an intensely hot area in the mantle below the earth 's crust . the heat that fuels the hot spot comes from very deep in the earth . this heat causes the mantle in that region to melt . the molten magma rises up and breaks through the crust to form a volcano . while the hot spot stays in one place , rooted to its deep source of heat , the tectonic plate is slowly moving above it . as the plate moves , so does the volcano , and another one forms in its place . the volcano that moved is no longer active . this is why a chain of extinct volcanoes is often found extending from a hot spot . hot spots are found around the globe , on land and in the ocean . the hawaiian islands are the youngest volcanic mountains in a long chain of volcanoes that formed over a hotspot . they are still forming today . another hot spot is under yellowstone national park , where the heat causes boiling mud pools and geysers like old faithful .
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while the hot spot stays in one place , rooted to its deep source of heat , the tectonic plate is slowly moving above it . as the plate moves , so does the volcano , and another one forms in its place . the volcano that moved is no longer active . this is why a chain of extinct volcanoes is often found extending from a hot spot .
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how do geologists know if a volcano is dormant ?
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some mountains are made of solid rock , like the rocky mountains or the swiss alps . but , some mountains are actually volcanoes . volcanoes are vents , or openings in the earth 's crust , that release ash , gases and steam , and hot liquid rock called lava . when the lava cools and hardens , it forms into the cone‐shaped mountain we think of as a volcano . most of the world 's volcanoes are found around the edges of tectonic plates , both on land and in the oceans . on land , volcanoes form when one tectonic plate moves under another . usually a thin , heavy oceanic plate subducts , or moves under , a thicker continental plate . when this happens , the ocean plate sinks into the mantle . water trapped in the rocks in this plate gets squeezed out . this causes some of the rocks to melt . the melted rock , or magma , is lighter than the surrounding rock and rises up . this magma collects in magma chambers , but it is still miles below the surface . when enough magma builds up in the magma chamber , it forces its way up to the surface and erupts , often causing volcanic eruptions . in the ocean , volcanoes erupt along cracks that are opened in the ocean floor by the spreading of two plates called a mid‐ocean ridge . magma from the earth 's upper mantle rises up to fill these cracks . as the lava cools , it forms new crust on the edges of the cracks . these mid‐ocean ridges are actually long chains of underwater volcanoes that circle the earth like the seams on a baseball . about 80 to 90 percent of all volcanic eruptions occur where the plates spread apart . hot spots some volcanoes pop up in random places , often far from the edge of a tectonic plate . these volcanoes are found over `` hot spots . '' a hot spot is an intensely hot area in the mantle below the earth 's crust . the heat that fuels the hot spot comes from very deep in the earth . this heat causes the mantle in that region to melt . the molten magma rises up and breaks through the crust to form a volcano . while the hot spot stays in one place , rooted to its deep source of heat , the tectonic plate is slowly moving above it . as the plate moves , so does the volcano , and another one forms in its place . the volcano that moved is no longer active . this is why a chain of extinct volcanoes is often found extending from a hot spot . hot spots are found around the globe , on land and in the ocean . the hawaiian islands are the youngest volcanic mountains in a long chain of volcanoes that formed over a hotspot . they are still forming today . another hot spot is under yellowstone national park , where the heat causes boiling mud pools and geysers like old faithful .
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when this happens , the ocean plate sinks into the mantle . water trapped in the rocks in this plate gets squeezed out . this causes some of the rocks to melt .
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in paragraph 4 , how does the water get trapped in the rocks in the first place and from where is it released ?
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overview john adams , a federalist , was the second president of the united states . he served from 1797-1801 . john adams 's presidency was marked by conflicts between the two newly-formed political parties : the federalists and the democratic-republicans . the conflicts between the two political parties centered on foreign policy and the balance of power between the federal government and the states ' governments . adams 's presidency the second person to take up the mantle of the presidency was john adams , who had served as vice president under george washington . adams was the nation ’ s first official federalist president ( although washington had been aligned with the ideas of the federalists , as president he had frowned on political parties and attempted to remain above partisan squabbling ) . during adams 's one-term presidency , the first two american political parties emerged and relations with france began to sour . rise of the the federalists and the democratic-republicans during the constitutional convention , factions emerged almost immediately . these factions ended up forming the first two political parties in american history : the federalists and the democratic-republicans . on one side , there were the federalists . generally , federalists lived along eastern seaboard and were wealthy merchants or well-educated people who lived in the city . they supported a stronger central government and a loose interpretation of the constitution : the idea that what the constitution did n't explicitly forbid , it allowed . the federalists also supported fixing the relationship between the united states and britain for trade reasons . on the other side were the democratic-republicans . the democratic-republicans frequently hailed from western regions and were more likely to be farmers than merchants . the democratic-republicans favored a weaker central government in favor of stronger state governments . they believed in a strict interpretation of the constitution : the idea that the federal government could n't do anything the constitution did n't explicitly permit . they also preferred a foreign alliance with france , as the french had supported the united states in the revolutionary war . check your understanding : can you fill in the missing information in the chart below ? beliefs | federalists | democratic-republicans -|-|- the federal government should be : | strong | weak state governments should be : | weak | the united states should ally with : | | france the constitution should be interpreted : | loosely | the xyz affair in 1794 , george washington sent john jay , the chief justice of the supreme court , to negotiate a treaty with the british that removed british forts from the northwest territory of the united states . he also hoped to negotiate free trade between the united states and the portion of the west indies which was occupied by the british . in exchange , the united states agreed to settle colonial debts that were owed to british merchants . known as jay 's treaty , the pro-british agreement angered the government of france , which had supported the united states in the american revolution . in response , the french navy began attacking american merchant ships . in 1797 , president adams sent diplomats to create a treaty between the united states and france . upon arrival , three french diplomats , nicknamed “ x ” , “ y ” , and “ z ” , proceeded to ask for bribes in order to start negotiations . the story eventually made its way to the american public , inciting many americans to write letters to adams , pushing for an armed conflict with the french . over the next two years , the united states carried on an undeclared naval war with france . the alien and sedition acts fear of opposition to the war within the united states prompted many federalists to call for a way to punish dissidents , chiefly those in the anti-federalist party . this took the form of the alien and sedition acts . “ alien ” refers to someone who is not from the country , and the alien act was created to allow the federal government to deport non-citizens who were a threat to national security . sedition means to write or speak in a way as to get people to rebel against the authority of a government . the sedition act , however , was created as a way to punish american citizens who criticized the american government during the war with the intent to harm the government ’ s position . under the sedition act , the government charged and prosecuted several printers who spoke against the united states and the war . even matthew lyon , a democratic-republican congress member , was jailed for criticizing president adams in a republican newspaper . the kentucky and virginia resolutions the federalist party supported the alien and sedition acts , but the democratic-republican party criticized them . they argued that the alien and sedition acts gave too much power to the federal government . thomas jefferson and james madison , leading democratic-republicans , each wrote a resolution that were later adopted by kentucky and virginia , respectively . these resolutions pushed for a strict interpretation of the constitution when it came to powers granted to the federal government . they also claimed that states had the power to ignore and disregard federal laws if they considered them outside of the bounds of their powers as described in the constitution . debate about the balance between federal and state power would continue until the civil war , remerging in issues like the nullification crisis . adams 's midnight appointments arguably , adams ’ most influential act as president happened as he was leaving office . in his last moments as president , the night before his successor ( thomas jefferson , a democratic-republican ) took office , adams attempted to appoint as many federalists as possible into empty positions as justices of the peace . these `` midnight judges '' were a ploy to stack the courts against the incoming democratic-republican party . although adams signed the judicial appointments , he failed to make sure they were delivered on time . when jefferson took office , he refused to arrange for the delivery of the remaining appointments . one of the disappointed would-be judges , william marbury , sued for his appointment . the supreme court case that followed , marbury v. madison , established the principle of judicial review : that the supreme court has the power to strike down laws if it judges that those laws violate the constitution . what do you think ? why did the adams administration pass the alien and sedition acts ? what was the most important issue dividing the federalists and the democratic republicans ?
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these `` midnight judges '' were a ploy to stack the courts against the incoming democratic-republican party . although adams signed the judicial appointments , he failed to make sure they were delivered on time . when jefferson took office , he refused to arrange for the delivery of the remaining appointments .
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how long were presidencies at this time ?
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged . one of the founders of this field was danish physicist niels bohr , who was interested in explaining the discrete line spectrum observed when light was emitted by different elements . bohr was also interested in the structure of the atom , which was a topic of much debate at the time . numerous models of the atom had been postulated based on experimental results including the discovery of the electron by j. j. thomson and the discovery of the nucleus by ernest rutherford . bohr supported the planetary model , in which electrons revolved around a positively charged nucleus like the rings around saturn—or alternatively , the planets around the sun . however , scientists still had many unanswered questions : $ $ where are the electrons , and what are they doing ? if the electrons are orbiting the nucleus , why don ’ t they fall into the nucleus as predicted by classical physics ? how is the internal structure of the atom related to the discrete emission lines produced by excited elements ? bohr addressed these questions using a seemingly simple assumption : what if some aspects of atomic structure , such as electron orbits and energies , could only take on certain values ? quantization and photons by the early 1900s , scientists were aware that some phenomena occurred in a discrete , as opposed to continuous , manner . physicists max planck and albert einstein had recently theorized that electromagnetic radiation not only behaves like a wave , but also sometimes like particles called photons . planck studied the electromagnetic radiation emitted by heated objects , and he proposed that the emitted electromagnetic radiation was `` quantized '' since the energy of light could only have values given by the following equation : $ e_ { \text { photon } } =nh\nu $ , where $ n $ is a positive integer , $ h $ is planck ’ s constant— $ 6.626 \times10^ { -34 } \ , \text { j } \cdot \text s $ —and $ \nu $ is the frequency of the light , which has units of $ \dfrac { 1 } { \text s } $ . as a consequence , the emitted electromagnetic radiation must have energies that are multiples of $ h\nu $ . einstein used planck 's results to explain why a minimum frequency of light was required to eject electrons from a metal surface in the photoelectric effect . when something is quantized , it means that only specific values are allowed , such as when playing a piano . since each key of a piano is tuned to a specific note , only a certain set of notes—which correspond to frequencies of sound waves—can be produced . as long as your piano is properly tuned , you can play an f or f sharp , but you ca n't play the note that is halfway between an f and f sharp . atomic line spectra atomic line spectra are another example of quantization . when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color . the emitted light can be refracted by a prism , producing spectra with a distinctive striped appearance due to the emission of certain wavelengths of light . for the relatively simple case of the hydrogen atom , the wavelengths of some emission lines could even be fitted to mathematical equations . the equations did not explain why the hydrogen atom emitted those particular wavelengths of light , however . prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ? bohr suggested that perhaps the electrons could only orbit the nucleus in specific orbits or shells with a fixed radius . only shells with a radius given by the equation below would be allowed , and the electron could not exist in between these shells . mathematically , we could write the allowed values of the atomic radius as $ r ( n ) =n^2\cdot r ( 1 ) $ , where $ n $ is a positive integer , and $ r ( 1 ) $ is the bohr radius , the smallest allowed radius for hydrogen . he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ . note that the energy is always going to be a negative number , and the ground state , $ n=1 $ , has the most negative value . this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ . since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu . \ \dfrac { \text c } { \lambda } & amp ; =\nu=\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~\text { divide both sides by c to solve for } \dfrac { 1 } { \lambda } .\ \ \dfrac { 1 } { \lambda } & amp ; =\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h\text c } \end { align } $ thus , we can see that the frequency—and wavelength—of the emitted photon depends on the energies of the initial and final shells of an electron in hydrogen . what have we learned since bohr proposed his model of hydrogen ? the bohr model worked beautifully for explaining the hydrogen atom and other single electron systems such as $ \text { he } ^+ $ . unfortunately , it did not do as well when applied to the spectra of more complex atoms . furthermore , the bohr model had no way of explaining why some lines are more intense than others or why some spectral lines split into multiple lines in the presence of a magnetic field—the zeeman effect . in the following decades , work by scientists such as erwin schrödinger showed that electrons can be thought of as behaving like waves and behaving as particles . this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level . bohr was the first to recognize this by incorporating the idea of quantization into the electronic structure of the hydrogen atom , and he was able to thereby explain the emission spectra of hydrogen as well as other one-electron systems .
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absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level .
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what is the reason for not radiating or absorbing energy ?
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged . one of the founders of this field was danish physicist niels bohr , who was interested in explaining the discrete line spectrum observed when light was emitted by different elements . bohr was also interested in the structure of the atom , which was a topic of much debate at the time . numerous models of the atom had been postulated based on experimental results including the discovery of the electron by j. j. thomson and the discovery of the nucleus by ernest rutherford . bohr supported the planetary model , in which electrons revolved around a positively charged nucleus like the rings around saturn—or alternatively , the planets around the sun . however , scientists still had many unanswered questions : $ $ where are the electrons , and what are they doing ? if the electrons are orbiting the nucleus , why don ’ t they fall into the nucleus as predicted by classical physics ? how is the internal structure of the atom related to the discrete emission lines produced by excited elements ? bohr addressed these questions using a seemingly simple assumption : what if some aspects of atomic structure , such as electron orbits and energies , could only take on certain values ? quantization and photons by the early 1900s , scientists were aware that some phenomena occurred in a discrete , as opposed to continuous , manner . physicists max planck and albert einstein had recently theorized that electromagnetic radiation not only behaves like a wave , but also sometimes like particles called photons . planck studied the electromagnetic radiation emitted by heated objects , and he proposed that the emitted electromagnetic radiation was `` quantized '' since the energy of light could only have values given by the following equation : $ e_ { \text { photon } } =nh\nu $ , where $ n $ is a positive integer , $ h $ is planck ’ s constant— $ 6.626 \times10^ { -34 } \ , \text { j } \cdot \text s $ —and $ \nu $ is the frequency of the light , which has units of $ \dfrac { 1 } { \text s } $ . as a consequence , the emitted electromagnetic radiation must have energies that are multiples of $ h\nu $ . einstein used planck 's results to explain why a minimum frequency of light was required to eject electrons from a metal surface in the photoelectric effect . when something is quantized , it means that only specific values are allowed , such as when playing a piano . since each key of a piano is tuned to a specific note , only a certain set of notes—which correspond to frequencies of sound waves—can be produced . as long as your piano is properly tuned , you can play an f or f sharp , but you ca n't play the note that is halfway between an f and f sharp . atomic line spectra atomic line spectra are another example of quantization . when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color . the emitted light can be refracted by a prism , producing spectra with a distinctive striped appearance due to the emission of certain wavelengths of light . for the relatively simple case of the hydrogen atom , the wavelengths of some emission lines could even be fitted to mathematical equations . the equations did not explain why the hydrogen atom emitted those particular wavelengths of light , however . prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ? bohr suggested that perhaps the electrons could only orbit the nucleus in specific orbits or shells with a fixed radius . only shells with a radius given by the equation below would be allowed , and the electron could not exist in between these shells . mathematically , we could write the allowed values of the atomic radius as $ r ( n ) =n^2\cdot r ( 1 ) $ , where $ n $ is a positive integer , and $ r ( 1 ) $ is the bohr radius , the smallest allowed radius for hydrogen . he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ . note that the energy is always going to be a negative number , and the ground state , $ n=1 $ , has the most negative value . this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ . since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu . \ \dfrac { \text c } { \lambda } & amp ; =\nu=\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~\text { divide both sides by c to solve for } \dfrac { 1 } { \lambda } .\ \ \dfrac { 1 } { \lambda } & amp ; =\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h\text c } \end { align } $ thus , we can see that the frequency—and wavelength—of the emitted photon depends on the energies of the initial and final shells of an electron in hydrogen . what have we learned since bohr proposed his model of hydrogen ? the bohr model worked beautifully for explaining the hydrogen atom and other single electron systems such as $ \text { he } ^+ $ . unfortunately , it did not do as well when applied to the spectra of more complex atoms . furthermore , the bohr model had no way of explaining why some lines are more intense than others or why some spectral lines split into multiple lines in the presence of a magnetic field—the zeeman effect . in the following decades , work by scientists such as erwin schrödinger showed that electrons can be thought of as behaving like waves and behaving as particles . this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level . bohr was the first to recognize this by incorporating the idea of quantization into the electronic structure of the hydrogen atom , and he was able to thereby explain the emission spectra of hydrogen as well as other one-electron systems .
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged .
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actually , i have heard that neutrons and protons are made up of quarks ( 6 kinds ?
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged . one of the founders of this field was danish physicist niels bohr , who was interested in explaining the discrete line spectrum observed when light was emitted by different elements . bohr was also interested in the structure of the atom , which was a topic of much debate at the time . numerous models of the atom had been postulated based on experimental results including the discovery of the electron by j. j. thomson and the discovery of the nucleus by ernest rutherford . bohr supported the planetary model , in which electrons revolved around a positively charged nucleus like the rings around saturn—or alternatively , the planets around the sun . however , scientists still had many unanswered questions : $ $ where are the electrons , and what are they doing ? if the electrons are orbiting the nucleus , why don ’ t they fall into the nucleus as predicted by classical physics ? how is the internal structure of the atom related to the discrete emission lines produced by excited elements ? bohr addressed these questions using a seemingly simple assumption : what if some aspects of atomic structure , such as electron orbits and energies , could only take on certain values ? quantization and photons by the early 1900s , scientists were aware that some phenomena occurred in a discrete , as opposed to continuous , manner . physicists max planck and albert einstein had recently theorized that electromagnetic radiation not only behaves like a wave , but also sometimes like particles called photons . planck studied the electromagnetic radiation emitted by heated objects , and he proposed that the emitted electromagnetic radiation was `` quantized '' since the energy of light could only have values given by the following equation : $ e_ { \text { photon } } =nh\nu $ , where $ n $ is a positive integer , $ h $ is planck ’ s constant— $ 6.626 \times10^ { -34 } \ , \text { j } \cdot \text s $ —and $ \nu $ is the frequency of the light , which has units of $ \dfrac { 1 } { \text s } $ . as a consequence , the emitted electromagnetic radiation must have energies that are multiples of $ h\nu $ . einstein used planck 's results to explain why a minimum frequency of light was required to eject electrons from a metal surface in the photoelectric effect . when something is quantized , it means that only specific values are allowed , such as when playing a piano . since each key of a piano is tuned to a specific note , only a certain set of notes—which correspond to frequencies of sound waves—can be produced . as long as your piano is properly tuned , you can play an f or f sharp , but you ca n't play the note that is halfway between an f and f sharp . atomic line spectra atomic line spectra are another example of quantization . when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color . the emitted light can be refracted by a prism , producing spectra with a distinctive striped appearance due to the emission of certain wavelengths of light . for the relatively simple case of the hydrogen atom , the wavelengths of some emission lines could even be fitted to mathematical equations . the equations did not explain why the hydrogen atom emitted those particular wavelengths of light , however . prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ? bohr suggested that perhaps the electrons could only orbit the nucleus in specific orbits or shells with a fixed radius . only shells with a radius given by the equation below would be allowed , and the electron could not exist in between these shells . mathematically , we could write the allowed values of the atomic radius as $ r ( n ) =n^2\cdot r ( 1 ) $ , where $ n $ is a positive integer , and $ r ( 1 ) $ is the bohr radius , the smallest allowed radius for hydrogen . he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ . note that the energy is always going to be a negative number , and the ground state , $ n=1 $ , has the most negative value . this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ . since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu . \ \dfrac { \text c } { \lambda } & amp ; =\nu=\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~\text { divide both sides by c to solve for } \dfrac { 1 } { \lambda } .\ \ \dfrac { 1 } { \lambda } & amp ; =\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h\text c } \end { align } $ thus , we can see that the frequency—and wavelength—of the emitted photon depends on the energies of the initial and final shells of an electron in hydrogen . what have we learned since bohr proposed his model of hydrogen ? the bohr model worked beautifully for explaining the hydrogen atom and other single electron systems such as $ \text { he } ^+ $ . unfortunately , it did not do as well when applied to the spectra of more complex atoms . furthermore , the bohr model had no way of explaining why some lines are more intense than others or why some spectral lines split into multiple lines in the presence of a magnetic field—the zeeman effect . in the following decades , work by scientists such as erwin schrödinger showed that electrons can be thought of as behaving like waves and behaving as particles . this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level . bohr was the first to recognize this by incorporating the idea of quantization into the electronic structure of the hydrogen atom , and he was able to thereby explain the emission spectra of hydrogen as well as other one-electron systems .
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the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu .
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what is the relationship between energy of light emitted and the periodic table ?
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged . one of the founders of this field was danish physicist niels bohr , who was interested in explaining the discrete line spectrum observed when light was emitted by different elements . bohr was also interested in the structure of the atom , which was a topic of much debate at the time . numerous models of the atom had been postulated based on experimental results including the discovery of the electron by j. j. thomson and the discovery of the nucleus by ernest rutherford . bohr supported the planetary model , in which electrons revolved around a positively charged nucleus like the rings around saturn—or alternatively , the planets around the sun . however , scientists still had many unanswered questions : $ $ where are the electrons , and what are they doing ? if the electrons are orbiting the nucleus , why don ’ t they fall into the nucleus as predicted by classical physics ? how is the internal structure of the atom related to the discrete emission lines produced by excited elements ? bohr addressed these questions using a seemingly simple assumption : what if some aspects of atomic structure , such as electron orbits and energies , could only take on certain values ? quantization and photons by the early 1900s , scientists were aware that some phenomena occurred in a discrete , as opposed to continuous , manner . physicists max planck and albert einstein had recently theorized that electromagnetic radiation not only behaves like a wave , but also sometimes like particles called photons . planck studied the electromagnetic radiation emitted by heated objects , and he proposed that the emitted electromagnetic radiation was `` quantized '' since the energy of light could only have values given by the following equation : $ e_ { \text { photon } } =nh\nu $ , where $ n $ is a positive integer , $ h $ is planck ’ s constant— $ 6.626 \times10^ { -34 } \ , \text { j } \cdot \text s $ —and $ \nu $ is the frequency of the light , which has units of $ \dfrac { 1 } { \text s } $ . as a consequence , the emitted electromagnetic radiation must have energies that are multiples of $ h\nu $ . einstein used planck 's results to explain why a minimum frequency of light was required to eject electrons from a metal surface in the photoelectric effect . when something is quantized , it means that only specific values are allowed , such as when playing a piano . since each key of a piano is tuned to a specific note , only a certain set of notes—which correspond to frequencies of sound waves—can be produced . as long as your piano is properly tuned , you can play an f or f sharp , but you ca n't play the note that is halfway between an f and f sharp . atomic line spectra atomic line spectra are another example of quantization . when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color . the emitted light can be refracted by a prism , producing spectra with a distinctive striped appearance due to the emission of certain wavelengths of light . for the relatively simple case of the hydrogen atom , the wavelengths of some emission lines could even be fitted to mathematical equations . the equations did not explain why the hydrogen atom emitted those particular wavelengths of light , however . prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ? bohr suggested that perhaps the electrons could only orbit the nucleus in specific orbits or shells with a fixed radius . only shells with a radius given by the equation below would be allowed , and the electron could not exist in between these shells . mathematically , we could write the allowed values of the atomic radius as $ r ( n ) =n^2\cdot r ( 1 ) $ , where $ n $ is a positive integer , and $ r ( 1 ) $ is the bohr radius , the smallest allowed radius for hydrogen . he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ . note that the energy is always going to be a negative number , and the ground state , $ n=1 $ , has the most negative value . this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ . since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu . \ \dfrac { \text c } { \lambda } & amp ; =\nu=\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~\text { divide both sides by c to solve for } \dfrac { 1 } { \lambda } .\ \ \dfrac { 1 } { \lambda } & amp ; =\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h\text c } \end { align } $ thus , we can see that the frequency—and wavelength—of the emitted photon depends on the energies of the initial and final shells of an electron in hydrogen . what have we learned since bohr proposed his model of hydrogen ? the bohr model worked beautifully for explaining the hydrogen atom and other single electron systems such as $ \text { he } ^+ $ . unfortunately , it did not do as well when applied to the spectra of more complex atoms . furthermore , the bohr model had no way of explaining why some lines are more intense than others or why some spectral lines split into multiple lines in the presence of a magnetic field—the zeeman effect . in the following decades , work by scientists such as erwin schrödinger showed that electrons can be thought of as behaving like waves and behaving as particles . this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level . bohr was the first to recognize this by incorporating the idea of quantization into the electronic structure of the hydrogen atom , and he was able to thereby explain the emission spectra of hydrogen as well as other one-electron systems .
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since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels .
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i was wondering , in the image representing the emission spectrum of sodium and the emission spectrum of the sun , how does this show that there is sodium in the sun 's atmosphere ?
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged . one of the founders of this field was danish physicist niels bohr , who was interested in explaining the discrete line spectrum observed when light was emitted by different elements . bohr was also interested in the structure of the atom , which was a topic of much debate at the time . numerous models of the atom had been postulated based on experimental results including the discovery of the electron by j. j. thomson and the discovery of the nucleus by ernest rutherford . bohr supported the planetary model , in which electrons revolved around a positively charged nucleus like the rings around saturn—or alternatively , the planets around the sun . however , scientists still had many unanswered questions : $ $ where are the electrons , and what are they doing ? if the electrons are orbiting the nucleus , why don ’ t they fall into the nucleus as predicted by classical physics ? how is the internal structure of the atom related to the discrete emission lines produced by excited elements ? bohr addressed these questions using a seemingly simple assumption : what if some aspects of atomic structure , such as electron orbits and energies , could only take on certain values ? quantization and photons by the early 1900s , scientists were aware that some phenomena occurred in a discrete , as opposed to continuous , manner . physicists max planck and albert einstein had recently theorized that electromagnetic radiation not only behaves like a wave , but also sometimes like particles called photons . planck studied the electromagnetic radiation emitted by heated objects , and he proposed that the emitted electromagnetic radiation was `` quantized '' since the energy of light could only have values given by the following equation : $ e_ { \text { photon } } =nh\nu $ , where $ n $ is a positive integer , $ h $ is planck ’ s constant— $ 6.626 \times10^ { -34 } \ , \text { j } \cdot \text s $ —and $ \nu $ is the frequency of the light , which has units of $ \dfrac { 1 } { \text s } $ . as a consequence , the emitted electromagnetic radiation must have energies that are multiples of $ h\nu $ . einstein used planck 's results to explain why a minimum frequency of light was required to eject electrons from a metal surface in the photoelectric effect . when something is quantized , it means that only specific values are allowed , such as when playing a piano . since each key of a piano is tuned to a specific note , only a certain set of notes—which correspond to frequencies of sound waves—can be produced . as long as your piano is properly tuned , you can play an f or f sharp , but you ca n't play the note that is halfway between an f and f sharp . atomic line spectra atomic line spectra are another example of quantization . when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color . the emitted light can be refracted by a prism , producing spectra with a distinctive striped appearance due to the emission of certain wavelengths of light . for the relatively simple case of the hydrogen atom , the wavelengths of some emission lines could even be fitted to mathematical equations . the equations did not explain why the hydrogen atom emitted those particular wavelengths of light , however . prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ? bohr suggested that perhaps the electrons could only orbit the nucleus in specific orbits or shells with a fixed radius . only shells with a radius given by the equation below would be allowed , and the electron could not exist in between these shells . mathematically , we could write the allowed values of the atomic radius as $ r ( n ) =n^2\cdot r ( 1 ) $ , where $ n $ is a positive integer , and $ r ( 1 ) $ is the bohr radius , the smallest allowed radius for hydrogen . he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ . note that the energy is always going to be a negative number , and the ground state , $ n=1 $ , has the most negative value . this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ . since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu . \ \dfrac { \text c } { \lambda } & amp ; =\nu=\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~\text { divide both sides by c to solve for } \dfrac { 1 } { \lambda } .\ \ \dfrac { 1 } { \lambda } & amp ; =\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h\text c } \end { align } $ thus , we can see that the frequency—and wavelength—of the emitted photon depends on the energies of the initial and final shells of an electron in hydrogen . what have we learned since bohr proposed his model of hydrogen ? the bohr model worked beautifully for explaining the hydrogen atom and other single electron systems such as $ \text { he } ^+ $ . unfortunately , it did not do as well when applied to the spectra of more complex atoms . furthermore , the bohr model had no way of explaining why some lines are more intense than others or why some spectral lines split into multiple lines in the presence of a magnetic field—the zeeman effect . in the following decades , work by scientists such as erwin schrödinger showed that electrons can be thought of as behaving like waves and behaving as particles . this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level . bohr was the first to recognize this by incorporating the idea of quantization into the electronic structure of the hydrogen atom , and he was able to thereby explain the emission spectra of hydrogen as well as other one-electron systems .
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prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ?
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why does'nt the bohr 's atomic model work for those atoms that have more than one electron ?
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged . one of the founders of this field was danish physicist niels bohr , who was interested in explaining the discrete line spectrum observed when light was emitted by different elements . bohr was also interested in the structure of the atom , which was a topic of much debate at the time . numerous models of the atom had been postulated based on experimental results including the discovery of the electron by j. j. thomson and the discovery of the nucleus by ernest rutherford . bohr supported the planetary model , in which electrons revolved around a positively charged nucleus like the rings around saturn—or alternatively , the planets around the sun . however , scientists still had many unanswered questions : $ $ where are the electrons , and what are they doing ? if the electrons are orbiting the nucleus , why don ’ t they fall into the nucleus as predicted by classical physics ? how is the internal structure of the atom related to the discrete emission lines produced by excited elements ? bohr addressed these questions using a seemingly simple assumption : what if some aspects of atomic structure , such as electron orbits and energies , could only take on certain values ? quantization and photons by the early 1900s , scientists were aware that some phenomena occurred in a discrete , as opposed to continuous , manner . physicists max planck and albert einstein had recently theorized that electromagnetic radiation not only behaves like a wave , but also sometimes like particles called photons . planck studied the electromagnetic radiation emitted by heated objects , and he proposed that the emitted electromagnetic radiation was `` quantized '' since the energy of light could only have values given by the following equation : $ e_ { \text { photon } } =nh\nu $ , where $ n $ is a positive integer , $ h $ is planck ’ s constant— $ 6.626 \times10^ { -34 } \ , \text { j } \cdot \text s $ —and $ \nu $ is the frequency of the light , which has units of $ \dfrac { 1 } { \text s } $ . as a consequence , the emitted electromagnetic radiation must have energies that are multiples of $ h\nu $ . einstein used planck 's results to explain why a minimum frequency of light was required to eject electrons from a metal surface in the photoelectric effect . when something is quantized , it means that only specific values are allowed , such as when playing a piano . since each key of a piano is tuned to a specific note , only a certain set of notes—which correspond to frequencies of sound waves—can be produced . as long as your piano is properly tuned , you can play an f or f sharp , but you ca n't play the note that is halfway between an f and f sharp . atomic line spectra atomic line spectra are another example of quantization . when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color . the emitted light can be refracted by a prism , producing spectra with a distinctive striped appearance due to the emission of certain wavelengths of light . for the relatively simple case of the hydrogen atom , the wavelengths of some emission lines could even be fitted to mathematical equations . the equations did not explain why the hydrogen atom emitted those particular wavelengths of light , however . prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ? bohr suggested that perhaps the electrons could only orbit the nucleus in specific orbits or shells with a fixed radius . only shells with a radius given by the equation below would be allowed , and the electron could not exist in between these shells . mathematically , we could write the allowed values of the atomic radius as $ r ( n ) =n^2\cdot r ( 1 ) $ , where $ n $ is a positive integer , and $ r ( 1 ) $ is the bohr radius , the smallest allowed radius for hydrogen . he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ . note that the energy is always going to be a negative number , and the ground state , $ n=1 $ , has the most negative value . this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ . since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu . \ \dfrac { \text c } { \lambda } & amp ; =\nu=\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~\text { divide both sides by c to solve for } \dfrac { 1 } { \lambda } .\ \ \dfrac { 1 } { \lambda } & amp ; =\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h\text c } \end { align } $ thus , we can see that the frequency—and wavelength—of the emitted photon depends on the energies of the initial and final shells of an electron in hydrogen . what have we learned since bohr proposed his model of hydrogen ? the bohr model worked beautifully for explaining the hydrogen atom and other single electron systems such as $ \text { he } ^+ $ . unfortunately , it did not do as well when applied to the spectra of more complex atoms . furthermore , the bohr model had no way of explaining why some lines are more intense than others or why some spectral lines split into multiple lines in the presence of a magnetic field—the zeeman effect . in the following decades , work by scientists such as erwin schrödinger showed that electrons can be thought of as behaving like waves and behaving as particles . this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level . bohr was the first to recognize this by incorporating the idea of quantization into the electronic structure of the hydrogen atom , and he was able to thereby explain the emission spectra of hydrogen as well as other one-electron systems .
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as long as your piano is properly tuned , you can play an f or f sharp , but you ca n't play the note that is halfway between an f and f sharp . atomic line spectra atomic line spectra are another example of quantization . when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color .
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how is atomic photon emission detected ?
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged . one of the founders of this field was danish physicist niels bohr , who was interested in explaining the discrete line spectrum observed when light was emitted by different elements . bohr was also interested in the structure of the atom , which was a topic of much debate at the time . numerous models of the atom had been postulated based on experimental results including the discovery of the electron by j. j. thomson and the discovery of the nucleus by ernest rutherford . bohr supported the planetary model , in which electrons revolved around a positively charged nucleus like the rings around saturn—or alternatively , the planets around the sun . however , scientists still had many unanswered questions : $ $ where are the electrons , and what are they doing ? if the electrons are orbiting the nucleus , why don ’ t they fall into the nucleus as predicted by classical physics ? how is the internal structure of the atom related to the discrete emission lines produced by excited elements ? bohr addressed these questions using a seemingly simple assumption : what if some aspects of atomic structure , such as electron orbits and energies , could only take on certain values ? quantization and photons by the early 1900s , scientists were aware that some phenomena occurred in a discrete , as opposed to continuous , manner . physicists max planck and albert einstein had recently theorized that electromagnetic radiation not only behaves like a wave , but also sometimes like particles called photons . planck studied the electromagnetic radiation emitted by heated objects , and he proposed that the emitted electromagnetic radiation was `` quantized '' since the energy of light could only have values given by the following equation : $ e_ { \text { photon } } =nh\nu $ , where $ n $ is a positive integer , $ h $ is planck ’ s constant— $ 6.626 \times10^ { -34 } \ , \text { j } \cdot \text s $ —and $ \nu $ is the frequency of the light , which has units of $ \dfrac { 1 } { \text s } $ . as a consequence , the emitted electromagnetic radiation must have energies that are multiples of $ h\nu $ . einstein used planck 's results to explain why a minimum frequency of light was required to eject electrons from a metal surface in the photoelectric effect . when something is quantized , it means that only specific values are allowed , such as when playing a piano . since each key of a piano is tuned to a specific note , only a certain set of notes—which correspond to frequencies of sound waves—can be produced . as long as your piano is properly tuned , you can play an f or f sharp , but you ca n't play the note that is halfway between an f and f sharp . atomic line spectra atomic line spectra are another example of quantization . when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color . the emitted light can be refracted by a prism , producing spectra with a distinctive striped appearance due to the emission of certain wavelengths of light . for the relatively simple case of the hydrogen atom , the wavelengths of some emission lines could even be fitted to mathematical equations . the equations did not explain why the hydrogen atom emitted those particular wavelengths of light , however . prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ? bohr suggested that perhaps the electrons could only orbit the nucleus in specific orbits or shells with a fixed radius . only shells with a radius given by the equation below would be allowed , and the electron could not exist in between these shells . mathematically , we could write the allowed values of the atomic radius as $ r ( n ) =n^2\cdot r ( 1 ) $ , where $ n $ is a positive integer , and $ r ( 1 ) $ is the bohr radius , the smallest allowed radius for hydrogen . he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ . note that the energy is always going to be a negative number , and the ground state , $ n=1 $ , has the most negative value . this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ . since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu . \ \dfrac { \text c } { \lambda } & amp ; =\nu=\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~\text { divide both sides by c to solve for } \dfrac { 1 } { \lambda } .\ \ \dfrac { 1 } { \lambda } & amp ; =\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h\text c } \end { align } $ thus , we can see that the frequency—and wavelength—of the emitted photon depends on the energies of the initial and final shells of an electron in hydrogen . what have we learned since bohr proposed his model of hydrogen ? the bohr model worked beautifully for explaining the hydrogen atom and other single electron systems such as $ \text { he } ^+ $ . unfortunately , it did not do as well when applied to the spectra of more complex atoms . furthermore , the bohr model had no way of explaining why some lines are more intense than others or why some spectral lines split into multiple lines in the presence of a magnetic field—the zeeman effect . in the following decades , work by scientists such as erwin schrödinger showed that electrons can be thought of as behaving like waves and behaving as particles . this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level . bohr was the first to recognize this by incorporating the idea of quantization into the electronic structure of the hydrogen atom , and he was able to thereby explain the emission spectra of hydrogen as well as other one-electron systems .
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prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ?
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also , how did bohr apply the concept of quantum energy in his model of the atom ?
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged . one of the founders of this field was danish physicist niels bohr , who was interested in explaining the discrete line spectrum observed when light was emitted by different elements . bohr was also interested in the structure of the atom , which was a topic of much debate at the time . numerous models of the atom had been postulated based on experimental results including the discovery of the electron by j. j. thomson and the discovery of the nucleus by ernest rutherford . bohr supported the planetary model , in which electrons revolved around a positively charged nucleus like the rings around saturn—or alternatively , the planets around the sun . however , scientists still had many unanswered questions : $ $ where are the electrons , and what are they doing ? if the electrons are orbiting the nucleus , why don ’ t they fall into the nucleus as predicted by classical physics ? how is the internal structure of the atom related to the discrete emission lines produced by excited elements ? bohr addressed these questions using a seemingly simple assumption : what if some aspects of atomic structure , such as electron orbits and energies , could only take on certain values ? quantization and photons by the early 1900s , scientists were aware that some phenomena occurred in a discrete , as opposed to continuous , manner . physicists max planck and albert einstein had recently theorized that electromagnetic radiation not only behaves like a wave , but also sometimes like particles called photons . planck studied the electromagnetic radiation emitted by heated objects , and he proposed that the emitted electromagnetic radiation was `` quantized '' since the energy of light could only have values given by the following equation : $ e_ { \text { photon } } =nh\nu $ , where $ n $ is a positive integer , $ h $ is planck ’ s constant— $ 6.626 \times10^ { -34 } \ , \text { j } \cdot \text s $ —and $ \nu $ is the frequency of the light , which has units of $ \dfrac { 1 } { \text s } $ . as a consequence , the emitted electromagnetic radiation must have energies that are multiples of $ h\nu $ . einstein used planck 's results to explain why a minimum frequency of light was required to eject electrons from a metal surface in the photoelectric effect . when something is quantized , it means that only specific values are allowed , such as when playing a piano . since each key of a piano is tuned to a specific note , only a certain set of notes—which correspond to frequencies of sound waves—can be produced . as long as your piano is properly tuned , you can play an f or f sharp , but you ca n't play the note that is halfway between an f and f sharp . atomic line spectra atomic line spectra are another example of quantization . when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color . the emitted light can be refracted by a prism , producing spectra with a distinctive striped appearance due to the emission of certain wavelengths of light . for the relatively simple case of the hydrogen atom , the wavelengths of some emission lines could even be fitted to mathematical equations . the equations did not explain why the hydrogen atom emitted those particular wavelengths of light , however . prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ? bohr suggested that perhaps the electrons could only orbit the nucleus in specific orbits or shells with a fixed radius . only shells with a radius given by the equation below would be allowed , and the electron could not exist in between these shells . mathematically , we could write the allowed values of the atomic radius as $ r ( n ) =n^2\cdot r ( 1 ) $ , where $ n $ is a positive integer , and $ r ( 1 ) $ is the bohr radius , the smallest allowed radius for hydrogen . he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ . note that the energy is always going to be a negative number , and the ground state , $ n=1 $ , has the most negative value . this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ . since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu . \ \dfrac { \text c } { \lambda } & amp ; =\nu=\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~\text { divide both sides by c to solve for } \dfrac { 1 } { \lambda } .\ \ \dfrac { 1 } { \lambda } & amp ; =\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h\text c } \end { align } $ thus , we can see that the frequency—and wavelength—of the emitted photon depends on the energies of the initial and final shells of an electron in hydrogen . what have we learned since bohr proposed his model of hydrogen ? the bohr model worked beautifully for explaining the hydrogen atom and other single electron systems such as $ \text { he } ^+ $ . unfortunately , it did not do as well when applied to the spectra of more complex atoms . furthermore , the bohr model had no way of explaining why some lines are more intense than others or why some spectral lines split into multiple lines in the presence of a magnetic field—the zeeman effect . in the following decades , work by scientists such as erwin schrödinger showed that electrons can be thought of as behaving like waves and behaving as particles . this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level . bohr was the first to recognize this by incorporating the idea of quantization into the electronic structure of the hydrogen atom , and he was able to thereby explain the emission spectra of hydrogen as well as other one-electron systems .
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this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus .
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what is the principle that defines plank 's constant ?
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged . one of the founders of this field was danish physicist niels bohr , who was interested in explaining the discrete line spectrum observed when light was emitted by different elements . bohr was also interested in the structure of the atom , which was a topic of much debate at the time . numerous models of the atom had been postulated based on experimental results including the discovery of the electron by j. j. thomson and the discovery of the nucleus by ernest rutherford . bohr supported the planetary model , in which electrons revolved around a positively charged nucleus like the rings around saturn—or alternatively , the planets around the sun . however , scientists still had many unanswered questions : $ $ where are the electrons , and what are they doing ? if the electrons are orbiting the nucleus , why don ’ t they fall into the nucleus as predicted by classical physics ? how is the internal structure of the atom related to the discrete emission lines produced by excited elements ? bohr addressed these questions using a seemingly simple assumption : what if some aspects of atomic structure , such as electron orbits and energies , could only take on certain values ? quantization and photons by the early 1900s , scientists were aware that some phenomena occurred in a discrete , as opposed to continuous , manner . physicists max planck and albert einstein had recently theorized that electromagnetic radiation not only behaves like a wave , but also sometimes like particles called photons . planck studied the electromagnetic radiation emitted by heated objects , and he proposed that the emitted electromagnetic radiation was `` quantized '' since the energy of light could only have values given by the following equation : $ e_ { \text { photon } } =nh\nu $ , where $ n $ is a positive integer , $ h $ is planck ’ s constant— $ 6.626 \times10^ { -34 } \ , \text { j } \cdot \text s $ —and $ \nu $ is the frequency of the light , which has units of $ \dfrac { 1 } { \text s } $ . as a consequence , the emitted electromagnetic radiation must have energies that are multiples of $ h\nu $ . einstein used planck 's results to explain why a minimum frequency of light was required to eject electrons from a metal surface in the photoelectric effect . when something is quantized , it means that only specific values are allowed , such as when playing a piano . since each key of a piano is tuned to a specific note , only a certain set of notes—which correspond to frequencies of sound waves—can be produced . as long as your piano is properly tuned , you can play an f or f sharp , but you ca n't play the note that is halfway between an f and f sharp . atomic line spectra atomic line spectra are another example of quantization . when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color . the emitted light can be refracted by a prism , producing spectra with a distinctive striped appearance due to the emission of certain wavelengths of light . for the relatively simple case of the hydrogen atom , the wavelengths of some emission lines could even be fitted to mathematical equations . the equations did not explain why the hydrogen atom emitted those particular wavelengths of light , however . prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ? bohr suggested that perhaps the electrons could only orbit the nucleus in specific orbits or shells with a fixed radius . only shells with a radius given by the equation below would be allowed , and the electron could not exist in between these shells . mathematically , we could write the allowed values of the atomic radius as $ r ( n ) =n^2\cdot r ( 1 ) $ , where $ n $ is a positive integer , and $ r ( 1 ) $ is the bohr radius , the smallest allowed radius for hydrogen . he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ . note that the energy is always going to be a negative number , and the ground state , $ n=1 $ , has the most negative value . this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ . since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu . \ \dfrac { \text c } { \lambda } & amp ; =\nu=\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~\text { divide both sides by c to solve for } \dfrac { 1 } { \lambda } .\ \ \dfrac { 1 } { \lambda } & amp ; =\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h\text c } \end { align } $ thus , we can see that the frequency—and wavelength—of the emitted photon depends on the energies of the initial and final shells of an electron in hydrogen . what have we learned since bohr proposed his model of hydrogen ? the bohr model worked beautifully for explaining the hydrogen atom and other single electron systems such as $ \text { he } ^+ $ . unfortunately , it did not do as well when applied to the spectra of more complex atoms . furthermore , the bohr model had no way of explaining why some lines are more intense than others or why some spectral lines split into multiple lines in the presence of a magnetic field—the zeeman effect . in the following decades , work by scientists such as erwin schrödinger showed that electrons can be thought of as behaving like waves and behaving as particles . this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level . bohr was the first to recognize this by incorporating the idea of quantization into the electronic structure of the hydrogen atom , and he was able to thereby explain the emission spectra of hydrogen as well as other one-electron systems .
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the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level .
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what exactly is this `` empty space '' ?
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged . one of the founders of this field was danish physicist niels bohr , who was interested in explaining the discrete line spectrum observed when light was emitted by different elements . bohr was also interested in the structure of the atom , which was a topic of much debate at the time . numerous models of the atom had been postulated based on experimental results including the discovery of the electron by j. j. thomson and the discovery of the nucleus by ernest rutherford . bohr supported the planetary model , in which electrons revolved around a positively charged nucleus like the rings around saturn—or alternatively , the planets around the sun . however , scientists still had many unanswered questions : $ $ where are the electrons , and what are they doing ? if the electrons are orbiting the nucleus , why don ’ t they fall into the nucleus as predicted by classical physics ? how is the internal structure of the atom related to the discrete emission lines produced by excited elements ? bohr addressed these questions using a seemingly simple assumption : what if some aspects of atomic structure , such as electron orbits and energies , could only take on certain values ? quantization and photons by the early 1900s , scientists were aware that some phenomena occurred in a discrete , as opposed to continuous , manner . physicists max planck and albert einstein had recently theorized that electromagnetic radiation not only behaves like a wave , but also sometimes like particles called photons . planck studied the electromagnetic radiation emitted by heated objects , and he proposed that the emitted electromagnetic radiation was `` quantized '' since the energy of light could only have values given by the following equation : $ e_ { \text { photon } } =nh\nu $ , where $ n $ is a positive integer , $ h $ is planck ’ s constant— $ 6.626 \times10^ { -34 } \ , \text { j } \cdot \text s $ —and $ \nu $ is the frequency of the light , which has units of $ \dfrac { 1 } { \text s } $ . as a consequence , the emitted electromagnetic radiation must have energies that are multiples of $ h\nu $ . einstein used planck 's results to explain why a minimum frequency of light was required to eject electrons from a metal surface in the photoelectric effect . when something is quantized , it means that only specific values are allowed , such as when playing a piano . since each key of a piano is tuned to a specific note , only a certain set of notes—which correspond to frequencies of sound waves—can be produced . as long as your piano is properly tuned , you can play an f or f sharp , but you ca n't play the note that is halfway between an f and f sharp . atomic line spectra atomic line spectra are another example of quantization . when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color . the emitted light can be refracted by a prism , producing spectra with a distinctive striped appearance due to the emission of certain wavelengths of light . for the relatively simple case of the hydrogen atom , the wavelengths of some emission lines could even be fitted to mathematical equations . the equations did not explain why the hydrogen atom emitted those particular wavelengths of light , however . prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ? bohr suggested that perhaps the electrons could only orbit the nucleus in specific orbits or shells with a fixed radius . only shells with a radius given by the equation below would be allowed , and the electron could not exist in between these shells . mathematically , we could write the allowed values of the atomic radius as $ r ( n ) =n^2\cdot r ( 1 ) $ , where $ n $ is a positive integer , and $ r ( 1 ) $ is the bohr radius , the smallest allowed radius for hydrogen . he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ . note that the energy is always going to be a negative number , and the ground state , $ n=1 $ , has the most negative value . this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ . since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu . \ \dfrac { \text c } { \lambda } & amp ; =\nu=\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~\text { divide both sides by c to solve for } \dfrac { 1 } { \lambda } .\ \ \dfrac { 1 } { \lambda } & amp ; =\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h\text c } \end { align } $ thus , we can see that the frequency—and wavelength—of the emitted photon depends on the energies of the initial and final shells of an electron in hydrogen . what have we learned since bohr proposed his model of hydrogen ? the bohr model worked beautifully for explaining the hydrogen atom and other single electron systems such as $ \text { he } ^+ $ . unfortunately , it did not do as well when applied to the spectra of more complex atoms . furthermore , the bohr model had no way of explaining why some lines are more intense than others or why some spectral lines split into multiple lines in the presence of a magnetic field—the zeeman effect . in the following decades , work by scientists such as erwin schrödinger showed that electrons can be thought of as behaving like waves and behaving as particles . this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level . bohr was the first to recognize this by incorporating the idea of quantization into the electronic structure of the hydrogen atom , and he was able to thereby explain the emission spectra of hydrogen as well as other one-electron systems .
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one of the founders of this field was danish physicist niels bohr , who was interested in explaining the discrete line spectrum observed when light was emitted by different elements . bohr was also interested in the structure of the atom , which was a topic of much debate at the time . numerous models of the atom had been postulated based on experimental results including the discovery of the electron by j. j. thomson and the discovery of the nucleus by ernest rutherford .
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how much size of an atom ?
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged . one of the founders of this field was danish physicist niels bohr , who was interested in explaining the discrete line spectrum observed when light was emitted by different elements . bohr was also interested in the structure of the atom , which was a topic of much debate at the time . numerous models of the atom had been postulated based on experimental results including the discovery of the electron by j. j. thomson and the discovery of the nucleus by ernest rutherford . bohr supported the planetary model , in which electrons revolved around a positively charged nucleus like the rings around saturn—or alternatively , the planets around the sun . however , scientists still had many unanswered questions : $ $ where are the electrons , and what are they doing ? if the electrons are orbiting the nucleus , why don ’ t they fall into the nucleus as predicted by classical physics ? how is the internal structure of the atom related to the discrete emission lines produced by excited elements ? bohr addressed these questions using a seemingly simple assumption : what if some aspects of atomic structure , such as electron orbits and energies , could only take on certain values ? quantization and photons by the early 1900s , scientists were aware that some phenomena occurred in a discrete , as opposed to continuous , manner . physicists max planck and albert einstein had recently theorized that electromagnetic radiation not only behaves like a wave , but also sometimes like particles called photons . planck studied the electromagnetic radiation emitted by heated objects , and he proposed that the emitted electromagnetic radiation was `` quantized '' since the energy of light could only have values given by the following equation : $ e_ { \text { photon } } =nh\nu $ , where $ n $ is a positive integer , $ h $ is planck ’ s constant— $ 6.626 \times10^ { -34 } \ , \text { j } \cdot \text s $ —and $ \nu $ is the frequency of the light , which has units of $ \dfrac { 1 } { \text s } $ . as a consequence , the emitted electromagnetic radiation must have energies that are multiples of $ h\nu $ . einstein used planck 's results to explain why a minimum frequency of light was required to eject electrons from a metal surface in the photoelectric effect . when something is quantized , it means that only specific values are allowed , such as when playing a piano . since each key of a piano is tuned to a specific note , only a certain set of notes—which correspond to frequencies of sound waves—can be produced . as long as your piano is properly tuned , you can play an f or f sharp , but you ca n't play the note that is halfway between an f and f sharp . atomic line spectra atomic line spectra are another example of quantization . when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color . the emitted light can be refracted by a prism , producing spectra with a distinctive striped appearance due to the emission of certain wavelengths of light . for the relatively simple case of the hydrogen atom , the wavelengths of some emission lines could even be fitted to mathematical equations . the equations did not explain why the hydrogen atom emitted those particular wavelengths of light , however . prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ? bohr suggested that perhaps the electrons could only orbit the nucleus in specific orbits or shells with a fixed radius . only shells with a radius given by the equation below would be allowed , and the electron could not exist in between these shells . mathematically , we could write the allowed values of the atomic radius as $ r ( n ) =n^2\cdot r ( 1 ) $ , where $ n $ is a positive integer , and $ r ( 1 ) $ is the bohr radius , the smallest allowed radius for hydrogen . he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ . note that the energy is always going to be a negative number , and the ground state , $ n=1 $ , has the most negative value . this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ . since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu . \ \dfrac { \text c } { \lambda } & amp ; =\nu=\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~\text { divide both sides by c to solve for } \dfrac { 1 } { \lambda } .\ \ \dfrac { 1 } { \lambda } & amp ; =\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h\text c } \end { align } $ thus , we can see that the frequency—and wavelength—of the emitted photon depends on the energies of the initial and final shells of an electron in hydrogen . what have we learned since bohr proposed his model of hydrogen ? the bohr model worked beautifully for explaining the hydrogen atom and other single electron systems such as $ \text { he } ^+ $ . unfortunately , it did not do as well when applied to the spectra of more complex atoms . furthermore , the bohr model had no way of explaining why some lines are more intense than others or why some spectral lines split into multiple lines in the presence of a magnetic field—the zeeman effect . in the following decades , work by scientists such as erwin schrödinger showed that electrons can be thought of as behaving like waves and behaving as particles . this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level . bohr was the first to recognize this by incorporating the idea of quantization into the electronic structure of the hydrogen atom , and he was able to thereby explain the emission spectra of hydrogen as well as other one-electron systems .
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according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen .
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why does the electron only fall down to the 2nd level when the 1st level is a lower configuration ?
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged . one of the founders of this field was danish physicist niels bohr , who was interested in explaining the discrete line spectrum observed when light was emitted by different elements . bohr was also interested in the structure of the atom , which was a topic of much debate at the time . numerous models of the atom had been postulated based on experimental results including the discovery of the electron by j. j. thomson and the discovery of the nucleus by ernest rutherford . bohr supported the planetary model , in which electrons revolved around a positively charged nucleus like the rings around saturn—or alternatively , the planets around the sun . however , scientists still had many unanswered questions : $ $ where are the electrons , and what are they doing ? if the electrons are orbiting the nucleus , why don ’ t they fall into the nucleus as predicted by classical physics ? how is the internal structure of the atom related to the discrete emission lines produced by excited elements ? bohr addressed these questions using a seemingly simple assumption : what if some aspects of atomic structure , such as electron orbits and energies , could only take on certain values ? quantization and photons by the early 1900s , scientists were aware that some phenomena occurred in a discrete , as opposed to continuous , manner . physicists max planck and albert einstein had recently theorized that electromagnetic radiation not only behaves like a wave , but also sometimes like particles called photons . planck studied the electromagnetic radiation emitted by heated objects , and he proposed that the emitted electromagnetic radiation was `` quantized '' since the energy of light could only have values given by the following equation : $ e_ { \text { photon } } =nh\nu $ , where $ n $ is a positive integer , $ h $ is planck ’ s constant— $ 6.626 \times10^ { -34 } \ , \text { j } \cdot \text s $ —and $ \nu $ is the frequency of the light , which has units of $ \dfrac { 1 } { \text s } $ . as a consequence , the emitted electromagnetic radiation must have energies that are multiples of $ h\nu $ . einstein used planck 's results to explain why a minimum frequency of light was required to eject electrons from a metal surface in the photoelectric effect . when something is quantized , it means that only specific values are allowed , such as when playing a piano . since each key of a piano is tuned to a specific note , only a certain set of notes—which correspond to frequencies of sound waves—can be produced . as long as your piano is properly tuned , you can play an f or f sharp , but you ca n't play the note that is halfway between an f and f sharp . atomic line spectra atomic line spectra are another example of quantization . when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color . the emitted light can be refracted by a prism , producing spectra with a distinctive striped appearance due to the emission of certain wavelengths of light . for the relatively simple case of the hydrogen atom , the wavelengths of some emission lines could even be fitted to mathematical equations . the equations did not explain why the hydrogen atom emitted those particular wavelengths of light , however . prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ? bohr suggested that perhaps the electrons could only orbit the nucleus in specific orbits or shells with a fixed radius . only shells with a radius given by the equation below would be allowed , and the electron could not exist in between these shells . mathematically , we could write the allowed values of the atomic radius as $ r ( n ) =n^2\cdot r ( 1 ) $ , where $ n $ is a positive integer , and $ r ( 1 ) $ is the bohr radius , the smallest allowed radius for hydrogen . he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ . note that the energy is always going to be a negative number , and the ground state , $ n=1 $ , has the most negative value . this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ . since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu . \ \dfrac { \text c } { \lambda } & amp ; =\nu=\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~\text { divide both sides by c to solve for } \dfrac { 1 } { \lambda } .\ \ \dfrac { 1 } { \lambda } & amp ; =\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h\text c } \end { align } $ thus , we can see that the frequency—and wavelength—of the emitted photon depends on the energies of the initial and final shells of an electron in hydrogen . what have we learned since bohr proposed his model of hydrogen ? the bohr model worked beautifully for explaining the hydrogen atom and other single electron systems such as $ \text { he } ^+ $ . unfortunately , it did not do as well when applied to the spectra of more complex atoms . furthermore , the bohr model had no way of explaining why some lines are more intense than others or why some spectral lines split into multiple lines in the presence of a magnetic field—the zeeman effect . in the following decades , work by scientists such as erwin schrödinger showed that electrons can be thought of as behaving like waves and behaving as particles . this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level . bohr was the first to recognize this by incorporating the idea of quantization into the electronic structure of the hydrogen atom , and he was able to thereby explain the emission spectra of hydrogen as well as other one-electron systems .
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according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition .
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i know when it falls down to the 1st level is called the lyman series , and why should there be any other hydrogen spectrum other than the lyman series ?
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged . one of the founders of this field was danish physicist niels bohr , who was interested in explaining the discrete line spectrum observed when light was emitted by different elements . bohr was also interested in the structure of the atom , which was a topic of much debate at the time . numerous models of the atom had been postulated based on experimental results including the discovery of the electron by j. j. thomson and the discovery of the nucleus by ernest rutherford . bohr supported the planetary model , in which electrons revolved around a positively charged nucleus like the rings around saturn—or alternatively , the planets around the sun . however , scientists still had many unanswered questions : $ $ where are the electrons , and what are they doing ? if the electrons are orbiting the nucleus , why don ’ t they fall into the nucleus as predicted by classical physics ? how is the internal structure of the atom related to the discrete emission lines produced by excited elements ? bohr addressed these questions using a seemingly simple assumption : what if some aspects of atomic structure , such as electron orbits and energies , could only take on certain values ? quantization and photons by the early 1900s , scientists were aware that some phenomena occurred in a discrete , as opposed to continuous , manner . physicists max planck and albert einstein had recently theorized that electromagnetic radiation not only behaves like a wave , but also sometimes like particles called photons . planck studied the electromagnetic radiation emitted by heated objects , and he proposed that the emitted electromagnetic radiation was `` quantized '' since the energy of light could only have values given by the following equation : $ e_ { \text { photon } } =nh\nu $ , where $ n $ is a positive integer , $ h $ is planck ’ s constant— $ 6.626 \times10^ { -34 } \ , \text { j } \cdot \text s $ —and $ \nu $ is the frequency of the light , which has units of $ \dfrac { 1 } { \text s } $ . as a consequence , the emitted electromagnetic radiation must have energies that are multiples of $ h\nu $ . einstein used planck 's results to explain why a minimum frequency of light was required to eject electrons from a metal surface in the photoelectric effect . when something is quantized , it means that only specific values are allowed , such as when playing a piano . since each key of a piano is tuned to a specific note , only a certain set of notes—which correspond to frequencies of sound waves—can be produced . as long as your piano is properly tuned , you can play an f or f sharp , but you ca n't play the note that is halfway between an f and f sharp . atomic line spectra atomic line spectra are another example of quantization . when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color . the emitted light can be refracted by a prism , producing spectra with a distinctive striped appearance due to the emission of certain wavelengths of light . for the relatively simple case of the hydrogen atom , the wavelengths of some emission lines could even be fitted to mathematical equations . the equations did not explain why the hydrogen atom emitted those particular wavelengths of light , however . prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ? bohr suggested that perhaps the electrons could only orbit the nucleus in specific orbits or shells with a fixed radius . only shells with a radius given by the equation below would be allowed , and the electron could not exist in between these shells . mathematically , we could write the allowed values of the atomic radius as $ r ( n ) =n^2\cdot r ( 1 ) $ , where $ n $ is a positive integer , and $ r ( 1 ) $ is the bohr radius , the smallest allowed radius for hydrogen . he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ . note that the energy is always going to be a negative number , and the ground state , $ n=1 $ , has the most negative value . this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ . since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu . \ \dfrac { \text c } { \lambda } & amp ; =\nu=\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~\text { divide both sides by c to solve for } \dfrac { 1 } { \lambda } .\ \ \dfrac { 1 } { \lambda } & amp ; =\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h\text c } \end { align } $ thus , we can see that the frequency—and wavelength—of the emitted photon depends on the energies of the initial and final shells of an electron in hydrogen . what have we learned since bohr proposed his model of hydrogen ? the bohr model worked beautifully for explaining the hydrogen atom and other single electron systems such as $ \text { he } ^+ $ . unfortunately , it did not do as well when applied to the spectra of more complex atoms . furthermore , the bohr model had no way of explaining why some lines are more intense than others or why some spectral lines split into multiple lines in the presence of a magnetic field—the zeeman effect . in the following decades , work by scientists such as erwin schrödinger showed that electrons can be thought of as behaving like waves and behaving as particles . this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level . bohr was the first to recognize this by incorporating the idea of quantization into the electronic structure of the hydrogen atom , and he was able to thereby explain the emission spectra of hydrogen as well as other one-electron systems .
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absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level .
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according to bohr also , electrons that are negatively charged revolve around the nucleus which is positively charged.so according to maxwell they must also release energy and their orbit should shrink but the energy level of orbit is fixed.why it is so ?
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged . one of the founders of this field was danish physicist niels bohr , who was interested in explaining the discrete line spectrum observed when light was emitted by different elements . bohr was also interested in the structure of the atom , which was a topic of much debate at the time . numerous models of the atom had been postulated based on experimental results including the discovery of the electron by j. j. thomson and the discovery of the nucleus by ernest rutherford . bohr supported the planetary model , in which electrons revolved around a positively charged nucleus like the rings around saturn—or alternatively , the planets around the sun . however , scientists still had many unanswered questions : $ $ where are the electrons , and what are they doing ? if the electrons are orbiting the nucleus , why don ’ t they fall into the nucleus as predicted by classical physics ? how is the internal structure of the atom related to the discrete emission lines produced by excited elements ? bohr addressed these questions using a seemingly simple assumption : what if some aspects of atomic structure , such as electron orbits and energies , could only take on certain values ? quantization and photons by the early 1900s , scientists were aware that some phenomena occurred in a discrete , as opposed to continuous , manner . physicists max planck and albert einstein had recently theorized that electromagnetic radiation not only behaves like a wave , but also sometimes like particles called photons . planck studied the electromagnetic radiation emitted by heated objects , and he proposed that the emitted electromagnetic radiation was `` quantized '' since the energy of light could only have values given by the following equation : $ e_ { \text { photon } } =nh\nu $ , where $ n $ is a positive integer , $ h $ is planck ’ s constant— $ 6.626 \times10^ { -34 } \ , \text { j } \cdot \text s $ —and $ \nu $ is the frequency of the light , which has units of $ \dfrac { 1 } { \text s } $ . as a consequence , the emitted electromagnetic radiation must have energies that are multiples of $ h\nu $ . einstein used planck 's results to explain why a minimum frequency of light was required to eject electrons from a metal surface in the photoelectric effect . when something is quantized , it means that only specific values are allowed , such as when playing a piano . since each key of a piano is tuned to a specific note , only a certain set of notes—which correspond to frequencies of sound waves—can be produced . as long as your piano is properly tuned , you can play an f or f sharp , but you ca n't play the note that is halfway between an f and f sharp . atomic line spectra atomic line spectra are another example of quantization . when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color . the emitted light can be refracted by a prism , producing spectra with a distinctive striped appearance due to the emission of certain wavelengths of light . for the relatively simple case of the hydrogen atom , the wavelengths of some emission lines could even be fitted to mathematical equations . the equations did not explain why the hydrogen atom emitted those particular wavelengths of light , however . prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ? bohr suggested that perhaps the electrons could only orbit the nucleus in specific orbits or shells with a fixed radius . only shells with a radius given by the equation below would be allowed , and the electron could not exist in between these shells . mathematically , we could write the allowed values of the atomic radius as $ r ( n ) =n^2\cdot r ( 1 ) $ , where $ n $ is a positive integer , and $ r ( 1 ) $ is the bohr radius , the smallest allowed radius for hydrogen . he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ . note that the energy is always going to be a negative number , and the ground state , $ n=1 $ , has the most negative value . this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ . since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu . \ \dfrac { \text c } { \lambda } & amp ; =\nu=\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~\text { divide both sides by c to solve for } \dfrac { 1 } { \lambda } .\ \ \dfrac { 1 } { \lambda } & amp ; =\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h\text c } \end { align } $ thus , we can see that the frequency—and wavelength—of the emitted photon depends on the energies of the initial and final shells of an electron in hydrogen . what have we learned since bohr proposed his model of hydrogen ? the bohr model worked beautifully for explaining the hydrogen atom and other single electron systems such as $ \text { he } ^+ $ . unfortunately , it did not do as well when applied to the spectra of more complex atoms . furthermore , the bohr model had no way of explaining why some lines are more intense than others or why some spectral lines split into multiple lines in the presence of a magnetic field—the zeeman effect . in the following decades , work by scientists such as erwin schrödinger showed that electrons can be thought of as behaving like waves and behaving as particles . this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level . bohr was the first to recognize this by incorporating the idea of quantization into the electronic structure of the hydrogen atom , and he was able to thereby explain the emission spectra of hydrogen as well as other one-electron systems .
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this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level .
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why can the square of the wave function be used to describe the probability density of finding electrons , as opposed to being able to absolutely determine where electrons are located in an atom ?
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged . one of the founders of this field was danish physicist niels bohr , who was interested in explaining the discrete line spectrum observed when light was emitted by different elements . bohr was also interested in the structure of the atom , which was a topic of much debate at the time . numerous models of the atom had been postulated based on experimental results including the discovery of the electron by j. j. thomson and the discovery of the nucleus by ernest rutherford . bohr supported the planetary model , in which electrons revolved around a positively charged nucleus like the rings around saturn—or alternatively , the planets around the sun . however , scientists still had many unanswered questions : $ $ where are the electrons , and what are they doing ? if the electrons are orbiting the nucleus , why don ’ t they fall into the nucleus as predicted by classical physics ? how is the internal structure of the atom related to the discrete emission lines produced by excited elements ? bohr addressed these questions using a seemingly simple assumption : what if some aspects of atomic structure , such as electron orbits and energies , could only take on certain values ? quantization and photons by the early 1900s , scientists were aware that some phenomena occurred in a discrete , as opposed to continuous , manner . physicists max planck and albert einstein had recently theorized that electromagnetic radiation not only behaves like a wave , but also sometimes like particles called photons . planck studied the electromagnetic radiation emitted by heated objects , and he proposed that the emitted electromagnetic radiation was `` quantized '' since the energy of light could only have values given by the following equation : $ e_ { \text { photon } } =nh\nu $ , where $ n $ is a positive integer , $ h $ is planck ’ s constant— $ 6.626 \times10^ { -34 } \ , \text { j } \cdot \text s $ —and $ \nu $ is the frequency of the light , which has units of $ \dfrac { 1 } { \text s } $ . as a consequence , the emitted electromagnetic radiation must have energies that are multiples of $ h\nu $ . einstein used planck 's results to explain why a minimum frequency of light was required to eject electrons from a metal surface in the photoelectric effect . when something is quantized , it means that only specific values are allowed , such as when playing a piano . since each key of a piano is tuned to a specific note , only a certain set of notes—which correspond to frequencies of sound waves—can be produced . as long as your piano is properly tuned , you can play an f or f sharp , but you ca n't play the note that is halfway between an f and f sharp . atomic line spectra atomic line spectra are another example of quantization . when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color . the emitted light can be refracted by a prism , producing spectra with a distinctive striped appearance due to the emission of certain wavelengths of light . for the relatively simple case of the hydrogen atom , the wavelengths of some emission lines could even be fitted to mathematical equations . the equations did not explain why the hydrogen atom emitted those particular wavelengths of light , however . prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ? bohr suggested that perhaps the electrons could only orbit the nucleus in specific orbits or shells with a fixed radius . only shells with a radius given by the equation below would be allowed , and the electron could not exist in between these shells . mathematically , we could write the allowed values of the atomic radius as $ r ( n ) =n^2\cdot r ( 1 ) $ , where $ n $ is a positive integer , and $ r ( 1 ) $ is the bohr radius , the smallest allowed radius for hydrogen . he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ . note that the energy is always going to be a negative number , and the ground state , $ n=1 $ , has the most negative value . this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ . since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu . \ \dfrac { \text c } { \lambda } & amp ; =\nu=\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~\text { divide both sides by c to solve for } \dfrac { 1 } { \lambda } .\ \ \dfrac { 1 } { \lambda } & amp ; =\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h\text c } \end { align } $ thus , we can see that the frequency—and wavelength—of the emitted photon depends on the energies of the initial and final shells of an electron in hydrogen . what have we learned since bohr proposed his model of hydrogen ? the bohr model worked beautifully for explaining the hydrogen atom and other single electron systems such as $ \text { he } ^+ $ . unfortunately , it did not do as well when applied to the spectra of more complex atoms . furthermore , the bohr model had no way of explaining why some lines are more intense than others or why some spectral lines split into multiple lines in the presence of a magnetic field—the zeeman effect . in the following decades , work by scientists such as erwin schrödinger showed that electrons can be thought of as behaving like waves and behaving as particles . this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level . bohr was the first to recognize this by incorporating the idea of quantization into the electronic structure of the hydrogen atom , and he was able to thereby explain the emission spectra of hydrogen as well as other one-electron systems .
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absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen .
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suppose a electron is excited to 5th energy level will it come directly to ground level or in numbers of steps ?
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged . one of the founders of this field was danish physicist niels bohr , who was interested in explaining the discrete line spectrum observed when light was emitted by different elements . bohr was also interested in the structure of the atom , which was a topic of much debate at the time . numerous models of the atom had been postulated based on experimental results including the discovery of the electron by j. j. thomson and the discovery of the nucleus by ernest rutherford . bohr supported the planetary model , in which electrons revolved around a positively charged nucleus like the rings around saturn—or alternatively , the planets around the sun . however , scientists still had many unanswered questions : $ $ where are the electrons , and what are they doing ? if the electrons are orbiting the nucleus , why don ’ t they fall into the nucleus as predicted by classical physics ? how is the internal structure of the atom related to the discrete emission lines produced by excited elements ? bohr addressed these questions using a seemingly simple assumption : what if some aspects of atomic structure , such as electron orbits and energies , could only take on certain values ? quantization and photons by the early 1900s , scientists were aware that some phenomena occurred in a discrete , as opposed to continuous , manner . physicists max planck and albert einstein had recently theorized that electromagnetic radiation not only behaves like a wave , but also sometimes like particles called photons . planck studied the electromagnetic radiation emitted by heated objects , and he proposed that the emitted electromagnetic radiation was `` quantized '' since the energy of light could only have values given by the following equation : $ e_ { \text { photon } } =nh\nu $ , where $ n $ is a positive integer , $ h $ is planck ’ s constant— $ 6.626 \times10^ { -34 } \ , \text { j } \cdot \text s $ —and $ \nu $ is the frequency of the light , which has units of $ \dfrac { 1 } { \text s } $ . as a consequence , the emitted electromagnetic radiation must have energies that are multiples of $ h\nu $ . einstein used planck 's results to explain why a minimum frequency of light was required to eject electrons from a metal surface in the photoelectric effect . when something is quantized , it means that only specific values are allowed , such as when playing a piano . since each key of a piano is tuned to a specific note , only a certain set of notes—which correspond to frequencies of sound waves—can be produced . as long as your piano is properly tuned , you can play an f or f sharp , but you ca n't play the note that is halfway between an f and f sharp . atomic line spectra atomic line spectra are another example of quantization . when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color . the emitted light can be refracted by a prism , producing spectra with a distinctive striped appearance due to the emission of certain wavelengths of light . for the relatively simple case of the hydrogen atom , the wavelengths of some emission lines could even be fitted to mathematical equations . the equations did not explain why the hydrogen atom emitted those particular wavelengths of light , however . prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ? bohr suggested that perhaps the electrons could only orbit the nucleus in specific orbits or shells with a fixed radius . only shells with a radius given by the equation below would be allowed , and the electron could not exist in between these shells . mathematically , we could write the allowed values of the atomic radius as $ r ( n ) =n^2\cdot r ( 1 ) $ , where $ n $ is a positive integer , and $ r ( 1 ) $ is the bohr radius , the smallest allowed radius for hydrogen . he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ . note that the energy is always going to be a negative number , and the ground state , $ n=1 $ , has the most negative value . this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ . since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu . \ \dfrac { \text c } { \lambda } & amp ; =\nu=\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~\text { divide both sides by c to solve for } \dfrac { 1 } { \lambda } .\ \ \dfrac { 1 } { \lambda } & amp ; =\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h\text c } \end { align } $ thus , we can see that the frequency—and wavelength—of the emitted photon depends on the energies of the initial and final shells of an electron in hydrogen . what have we learned since bohr proposed his model of hydrogen ? the bohr model worked beautifully for explaining the hydrogen atom and other single electron systems such as $ \text { he } ^+ $ . unfortunately , it did not do as well when applied to the spectra of more complex atoms . furthermore , the bohr model had no way of explaining why some lines are more intense than others or why some spectral lines split into multiple lines in the presence of a magnetic field—the zeeman effect . in the following decades , work by scientists such as erwin schrödinger showed that electrons can be thought of as behaving like waves and behaving as particles . this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level . bohr was the first to recognize this by incorporating the idea of quantization into the electronic structure of the hydrogen atom , and he was able to thereby explain the emission spectra of hydrogen as well as other one-electron systems .
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absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level .
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the energy required to excite an electron , is it an ionizing radiation ?
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged . one of the founders of this field was danish physicist niels bohr , who was interested in explaining the discrete line spectrum observed when light was emitted by different elements . bohr was also interested in the structure of the atom , which was a topic of much debate at the time . numerous models of the atom had been postulated based on experimental results including the discovery of the electron by j. j. thomson and the discovery of the nucleus by ernest rutherford . bohr supported the planetary model , in which electrons revolved around a positively charged nucleus like the rings around saturn—or alternatively , the planets around the sun . however , scientists still had many unanswered questions : $ $ where are the electrons , and what are they doing ? if the electrons are orbiting the nucleus , why don ’ t they fall into the nucleus as predicted by classical physics ? how is the internal structure of the atom related to the discrete emission lines produced by excited elements ? bohr addressed these questions using a seemingly simple assumption : what if some aspects of atomic structure , such as electron orbits and energies , could only take on certain values ? quantization and photons by the early 1900s , scientists were aware that some phenomena occurred in a discrete , as opposed to continuous , manner . physicists max planck and albert einstein had recently theorized that electromagnetic radiation not only behaves like a wave , but also sometimes like particles called photons . planck studied the electromagnetic radiation emitted by heated objects , and he proposed that the emitted electromagnetic radiation was `` quantized '' since the energy of light could only have values given by the following equation : $ e_ { \text { photon } } =nh\nu $ , where $ n $ is a positive integer , $ h $ is planck ’ s constant— $ 6.626 \times10^ { -34 } \ , \text { j } \cdot \text s $ —and $ \nu $ is the frequency of the light , which has units of $ \dfrac { 1 } { \text s } $ . as a consequence , the emitted electromagnetic radiation must have energies that are multiples of $ h\nu $ . einstein used planck 's results to explain why a minimum frequency of light was required to eject electrons from a metal surface in the photoelectric effect . when something is quantized , it means that only specific values are allowed , such as when playing a piano . since each key of a piano is tuned to a specific note , only a certain set of notes—which correspond to frequencies of sound waves—can be produced . as long as your piano is properly tuned , you can play an f or f sharp , but you ca n't play the note that is halfway between an f and f sharp . atomic line spectra atomic line spectra are another example of quantization . when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color . the emitted light can be refracted by a prism , producing spectra with a distinctive striped appearance due to the emission of certain wavelengths of light . for the relatively simple case of the hydrogen atom , the wavelengths of some emission lines could even be fitted to mathematical equations . the equations did not explain why the hydrogen atom emitted those particular wavelengths of light , however . prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ? bohr suggested that perhaps the electrons could only orbit the nucleus in specific orbits or shells with a fixed radius . only shells with a radius given by the equation below would be allowed , and the electron could not exist in between these shells . mathematically , we could write the allowed values of the atomic radius as $ r ( n ) =n^2\cdot r ( 1 ) $ , where $ n $ is a positive integer , and $ r ( 1 ) $ is the bohr radius , the smallest allowed radius for hydrogen . he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ . note that the energy is always going to be a negative number , and the ground state , $ n=1 $ , has the most negative value . this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ . since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu . \ \dfrac { \text c } { \lambda } & amp ; =\nu=\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~\text { divide both sides by c to solve for } \dfrac { 1 } { \lambda } .\ \ \dfrac { 1 } { \lambda } & amp ; =\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h\text c } \end { align } $ thus , we can see that the frequency—and wavelength—of the emitted photon depends on the energies of the initial and final shells of an electron in hydrogen . what have we learned since bohr proposed his model of hydrogen ? the bohr model worked beautifully for explaining the hydrogen atom and other single electron systems such as $ \text { he } ^+ $ . unfortunately , it did not do as well when applied to the spectra of more complex atoms . furthermore , the bohr model had no way of explaining why some lines are more intense than others or why some spectral lines split into multiple lines in the presence of a magnetic field—the zeeman effect . in the following decades , work by scientists such as erwin schrödinger showed that electrons can be thought of as behaving like waves and behaving as particles . this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level . bohr was the first to recognize this by incorporating the idea of quantization into the electronic structure of the hydrogen atom , and he was able to thereby explain the emission spectra of hydrogen as well as other one-electron systems .
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this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ . since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure .
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why the energy of an electron is always negative ?
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged . one of the founders of this field was danish physicist niels bohr , who was interested in explaining the discrete line spectrum observed when light was emitted by different elements . bohr was also interested in the structure of the atom , which was a topic of much debate at the time . numerous models of the atom had been postulated based on experimental results including the discovery of the electron by j. j. thomson and the discovery of the nucleus by ernest rutherford . bohr supported the planetary model , in which electrons revolved around a positively charged nucleus like the rings around saturn—or alternatively , the planets around the sun . however , scientists still had many unanswered questions : $ $ where are the electrons , and what are they doing ? if the electrons are orbiting the nucleus , why don ’ t they fall into the nucleus as predicted by classical physics ? how is the internal structure of the atom related to the discrete emission lines produced by excited elements ? bohr addressed these questions using a seemingly simple assumption : what if some aspects of atomic structure , such as electron orbits and energies , could only take on certain values ? quantization and photons by the early 1900s , scientists were aware that some phenomena occurred in a discrete , as opposed to continuous , manner . physicists max planck and albert einstein had recently theorized that electromagnetic radiation not only behaves like a wave , but also sometimes like particles called photons . planck studied the electromagnetic radiation emitted by heated objects , and he proposed that the emitted electromagnetic radiation was `` quantized '' since the energy of light could only have values given by the following equation : $ e_ { \text { photon } } =nh\nu $ , where $ n $ is a positive integer , $ h $ is planck ’ s constant— $ 6.626 \times10^ { -34 } \ , \text { j } \cdot \text s $ —and $ \nu $ is the frequency of the light , which has units of $ \dfrac { 1 } { \text s } $ . as a consequence , the emitted electromagnetic radiation must have energies that are multiples of $ h\nu $ . einstein used planck 's results to explain why a minimum frequency of light was required to eject electrons from a metal surface in the photoelectric effect . when something is quantized , it means that only specific values are allowed , such as when playing a piano . since each key of a piano is tuned to a specific note , only a certain set of notes—which correspond to frequencies of sound waves—can be produced . as long as your piano is properly tuned , you can play an f or f sharp , but you ca n't play the note that is halfway between an f and f sharp . atomic line spectra atomic line spectra are another example of quantization . when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color . the emitted light can be refracted by a prism , producing spectra with a distinctive striped appearance due to the emission of certain wavelengths of light . for the relatively simple case of the hydrogen atom , the wavelengths of some emission lines could even be fitted to mathematical equations . the equations did not explain why the hydrogen atom emitted those particular wavelengths of light , however . prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ? bohr suggested that perhaps the electrons could only orbit the nucleus in specific orbits or shells with a fixed radius . only shells with a radius given by the equation below would be allowed , and the electron could not exist in between these shells . mathematically , we could write the allowed values of the atomic radius as $ r ( n ) =n^2\cdot r ( 1 ) $ , where $ n $ is a positive integer , and $ r ( 1 ) $ is the bohr radius , the smallest allowed radius for hydrogen . he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ . note that the energy is always going to be a negative number , and the ground state , $ n=1 $ , has the most negative value . this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ . since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu . \ \dfrac { \text c } { \lambda } & amp ; =\nu=\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~\text { divide both sides by c to solve for } \dfrac { 1 } { \lambda } .\ \ \dfrac { 1 } { \lambda } & amp ; =\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h\text c } \end { align } $ thus , we can see that the frequency—and wavelength—of the emitted photon depends on the energies of the initial and final shells of an electron in hydrogen . what have we learned since bohr proposed his model of hydrogen ? the bohr model worked beautifully for explaining the hydrogen atom and other single electron systems such as $ \text { he } ^+ $ . unfortunately , it did not do as well when applied to the spectra of more complex atoms . furthermore , the bohr model had no way of explaining why some lines are more intense than others or why some spectral lines split into multiple lines in the presence of a magnetic field—the zeeman effect . in the following decades , work by scientists such as erwin schrödinger showed that electrons can be thought of as behaving like waves and behaving as particles . this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level . bohr was the first to recognize this by incorporating the idea of quantization into the electronic structure of the hydrogen atom , and he was able to thereby explain the emission spectra of hydrogen as well as other one-electron systems .
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he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ . note that the energy is always going to be a negative number , and the ground state , $ n=1 $ , has the most negative value . this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ .
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did the negative sign convey that that much of energy is required or that much is realised ?
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged . one of the founders of this field was danish physicist niels bohr , who was interested in explaining the discrete line spectrum observed when light was emitted by different elements . bohr was also interested in the structure of the atom , which was a topic of much debate at the time . numerous models of the atom had been postulated based on experimental results including the discovery of the electron by j. j. thomson and the discovery of the nucleus by ernest rutherford . bohr supported the planetary model , in which electrons revolved around a positively charged nucleus like the rings around saturn—or alternatively , the planets around the sun . however , scientists still had many unanswered questions : $ $ where are the electrons , and what are they doing ? if the electrons are orbiting the nucleus , why don ’ t they fall into the nucleus as predicted by classical physics ? how is the internal structure of the atom related to the discrete emission lines produced by excited elements ? bohr addressed these questions using a seemingly simple assumption : what if some aspects of atomic structure , such as electron orbits and energies , could only take on certain values ? quantization and photons by the early 1900s , scientists were aware that some phenomena occurred in a discrete , as opposed to continuous , manner . physicists max planck and albert einstein had recently theorized that electromagnetic radiation not only behaves like a wave , but also sometimes like particles called photons . planck studied the electromagnetic radiation emitted by heated objects , and he proposed that the emitted electromagnetic radiation was `` quantized '' since the energy of light could only have values given by the following equation : $ e_ { \text { photon } } =nh\nu $ , where $ n $ is a positive integer , $ h $ is planck ’ s constant— $ 6.626 \times10^ { -34 } \ , \text { j } \cdot \text s $ —and $ \nu $ is the frequency of the light , which has units of $ \dfrac { 1 } { \text s } $ . as a consequence , the emitted electromagnetic radiation must have energies that are multiples of $ h\nu $ . einstein used planck 's results to explain why a minimum frequency of light was required to eject electrons from a metal surface in the photoelectric effect . when something is quantized , it means that only specific values are allowed , such as when playing a piano . since each key of a piano is tuned to a specific note , only a certain set of notes—which correspond to frequencies of sound waves—can be produced . as long as your piano is properly tuned , you can play an f or f sharp , but you ca n't play the note that is halfway between an f and f sharp . atomic line spectra atomic line spectra are another example of quantization . when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color . the emitted light can be refracted by a prism , producing spectra with a distinctive striped appearance due to the emission of certain wavelengths of light . for the relatively simple case of the hydrogen atom , the wavelengths of some emission lines could even be fitted to mathematical equations . the equations did not explain why the hydrogen atom emitted those particular wavelengths of light , however . prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ? bohr suggested that perhaps the electrons could only orbit the nucleus in specific orbits or shells with a fixed radius . only shells with a radius given by the equation below would be allowed , and the electron could not exist in between these shells . mathematically , we could write the allowed values of the atomic radius as $ r ( n ) =n^2\cdot r ( 1 ) $ , where $ n $ is a positive integer , and $ r ( 1 ) $ is the bohr radius , the smallest allowed radius for hydrogen . he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ . note that the energy is always going to be a negative number , and the ground state , $ n=1 $ , has the most negative value . this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ . since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu . \ \dfrac { \text c } { \lambda } & amp ; =\nu=\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~\text { divide both sides by c to solve for } \dfrac { 1 } { \lambda } .\ \ \dfrac { 1 } { \lambda } & amp ; =\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h\text c } \end { align } $ thus , we can see that the frequency—and wavelength—of the emitted photon depends on the energies of the initial and final shells of an electron in hydrogen . what have we learned since bohr proposed his model of hydrogen ? the bohr model worked beautifully for explaining the hydrogen atom and other single electron systems such as $ \text { he } ^+ $ . unfortunately , it did not do as well when applied to the spectra of more complex atoms . furthermore , the bohr model had no way of explaining why some lines are more intense than others or why some spectral lines split into multiple lines in the presence of a magnetic field—the zeeman effect . in the following decades , work by scientists such as erwin schrödinger showed that electrons can be thought of as behaving like waves and behaving as particles . this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level . bohr was the first to recognize this by incorporating the idea of quantization into the electronic structure of the hydrogen atom , and he was able to thereby explain the emission spectra of hydrogen as well as other one-electron systems .
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the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu .
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what is the difference between a photon and quantum ?
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged . one of the founders of this field was danish physicist niels bohr , who was interested in explaining the discrete line spectrum observed when light was emitted by different elements . bohr was also interested in the structure of the atom , which was a topic of much debate at the time . numerous models of the atom had been postulated based on experimental results including the discovery of the electron by j. j. thomson and the discovery of the nucleus by ernest rutherford . bohr supported the planetary model , in which electrons revolved around a positively charged nucleus like the rings around saturn—or alternatively , the planets around the sun . however , scientists still had many unanswered questions : $ $ where are the electrons , and what are they doing ? if the electrons are orbiting the nucleus , why don ’ t they fall into the nucleus as predicted by classical physics ? how is the internal structure of the atom related to the discrete emission lines produced by excited elements ? bohr addressed these questions using a seemingly simple assumption : what if some aspects of atomic structure , such as electron orbits and energies , could only take on certain values ? quantization and photons by the early 1900s , scientists were aware that some phenomena occurred in a discrete , as opposed to continuous , manner . physicists max planck and albert einstein had recently theorized that electromagnetic radiation not only behaves like a wave , but also sometimes like particles called photons . planck studied the electromagnetic radiation emitted by heated objects , and he proposed that the emitted electromagnetic radiation was `` quantized '' since the energy of light could only have values given by the following equation : $ e_ { \text { photon } } =nh\nu $ , where $ n $ is a positive integer , $ h $ is planck ’ s constant— $ 6.626 \times10^ { -34 } \ , \text { j } \cdot \text s $ —and $ \nu $ is the frequency of the light , which has units of $ \dfrac { 1 } { \text s } $ . as a consequence , the emitted electromagnetic radiation must have energies that are multiples of $ h\nu $ . einstein used planck 's results to explain why a minimum frequency of light was required to eject electrons from a metal surface in the photoelectric effect . when something is quantized , it means that only specific values are allowed , such as when playing a piano . since each key of a piano is tuned to a specific note , only a certain set of notes—which correspond to frequencies of sound waves—can be produced . as long as your piano is properly tuned , you can play an f or f sharp , but you ca n't play the note that is halfway between an f and f sharp . atomic line spectra atomic line spectra are another example of quantization . when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color . the emitted light can be refracted by a prism , producing spectra with a distinctive striped appearance due to the emission of certain wavelengths of light . for the relatively simple case of the hydrogen atom , the wavelengths of some emission lines could even be fitted to mathematical equations . the equations did not explain why the hydrogen atom emitted those particular wavelengths of light , however . prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ? bohr suggested that perhaps the electrons could only orbit the nucleus in specific orbits or shells with a fixed radius . only shells with a radius given by the equation below would be allowed , and the electron could not exist in between these shells . mathematically , we could write the allowed values of the atomic radius as $ r ( n ) =n^2\cdot r ( 1 ) $ , where $ n $ is a positive integer , and $ r ( 1 ) $ is the bohr radius , the smallest allowed radius for hydrogen . he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ . note that the energy is always going to be a negative number , and the ground state , $ n=1 $ , has the most negative value . this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ . since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu . \ \dfrac { \text c } { \lambda } & amp ; =\nu=\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~\text { divide both sides by c to solve for } \dfrac { 1 } { \lambda } .\ \ \dfrac { 1 } { \lambda } & amp ; =\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h\text c } \end { align } $ thus , we can see that the frequency—and wavelength—of the emitted photon depends on the energies of the initial and final shells of an electron in hydrogen . what have we learned since bohr proposed his model of hydrogen ? the bohr model worked beautifully for explaining the hydrogen atom and other single electron systems such as $ \text { he } ^+ $ . unfortunately , it did not do as well when applied to the spectra of more complex atoms . furthermore , the bohr model had no way of explaining why some lines are more intense than others or why some spectral lines split into multiple lines in the presence of a magnetic field—the zeeman effect . in the following decades , work by scientists such as erwin schrödinger showed that electrons can be thought of as behaving like waves and behaving as particles . this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level . bohr was the first to recognize this by incorporating the idea of quantization into the electronic structure of the hydrogen atom , and he was able to thereby explain the emission spectra of hydrogen as well as other one-electron systems .
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only shells with a radius given by the equation below would be allowed , and the electron could not exist in between these shells . mathematically , we could write the allowed values of the atomic radius as $ r ( n ) =n^2\cdot r ( 1 ) $ , where $ n $ is a positive integer , and $ r ( 1 ) $ is the bohr radius , the smallest allowed radius for hydrogen . he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ .
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what does `` n '' mean in this formula ?
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged . one of the founders of this field was danish physicist niels bohr , who was interested in explaining the discrete line spectrum observed when light was emitted by different elements . bohr was also interested in the structure of the atom , which was a topic of much debate at the time . numerous models of the atom had been postulated based on experimental results including the discovery of the electron by j. j. thomson and the discovery of the nucleus by ernest rutherford . bohr supported the planetary model , in which electrons revolved around a positively charged nucleus like the rings around saturn—or alternatively , the planets around the sun . however , scientists still had many unanswered questions : $ $ where are the electrons , and what are they doing ? if the electrons are orbiting the nucleus , why don ’ t they fall into the nucleus as predicted by classical physics ? how is the internal structure of the atom related to the discrete emission lines produced by excited elements ? bohr addressed these questions using a seemingly simple assumption : what if some aspects of atomic structure , such as electron orbits and energies , could only take on certain values ? quantization and photons by the early 1900s , scientists were aware that some phenomena occurred in a discrete , as opposed to continuous , manner . physicists max planck and albert einstein had recently theorized that electromagnetic radiation not only behaves like a wave , but also sometimes like particles called photons . planck studied the electromagnetic radiation emitted by heated objects , and he proposed that the emitted electromagnetic radiation was `` quantized '' since the energy of light could only have values given by the following equation : $ e_ { \text { photon } } =nh\nu $ , where $ n $ is a positive integer , $ h $ is planck ’ s constant— $ 6.626 \times10^ { -34 } \ , \text { j } \cdot \text s $ —and $ \nu $ is the frequency of the light , which has units of $ \dfrac { 1 } { \text s } $ . as a consequence , the emitted electromagnetic radiation must have energies that are multiples of $ h\nu $ . einstein used planck 's results to explain why a minimum frequency of light was required to eject electrons from a metal surface in the photoelectric effect . when something is quantized , it means that only specific values are allowed , such as when playing a piano . since each key of a piano is tuned to a specific note , only a certain set of notes—which correspond to frequencies of sound waves—can be produced . as long as your piano is properly tuned , you can play an f or f sharp , but you ca n't play the note that is halfway between an f and f sharp . atomic line spectra atomic line spectra are another example of quantization . when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color . the emitted light can be refracted by a prism , producing spectra with a distinctive striped appearance due to the emission of certain wavelengths of light . for the relatively simple case of the hydrogen atom , the wavelengths of some emission lines could even be fitted to mathematical equations . the equations did not explain why the hydrogen atom emitted those particular wavelengths of light , however . prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ? bohr suggested that perhaps the electrons could only orbit the nucleus in specific orbits or shells with a fixed radius . only shells with a radius given by the equation below would be allowed , and the electron could not exist in between these shells . mathematically , we could write the allowed values of the atomic radius as $ r ( n ) =n^2\cdot r ( 1 ) $ , where $ n $ is a positive integer , and $ r ( 1 ) $ is the bohr radius , the smallest allowed radius for hydrogen . he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ . note that the energy is always going to be a negative number , and the ground state , $ n=1 $ , has the most negative value . this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ . since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu . \ \dfrac { \text c } { \lambda } & amp ; =\nu=\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~\text { divide both sides by c to solve for } \dfrac { 1 } { \lambda } .\ \ \dfrac { 1 } { \lambda } & amp ; =\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h\text c } \end { align } $ thus , we can see that the frequency—and wavelength—of the emitted photon depends on the energies of the initial and final shells of an electron in hydrogen . what have we learned since bohr proposed his model of hydrogen ? the bohr model worked beautifully for explaining the hydrogen atom and other single electron systems such as $ \text { he } ^+ $ . unfortunately , it did not do as well when applied to the spectra of more complex atoms . furthermore , the bohr model had no way of explaining why some lines are more intense than others or why some spectral lines split into multiple lines in the presence of a magnetic field—the zeeman effect . in the following decades , work by scientists such as erwin schrödinger showed that electrons can be thought of as behaving like waves and behaving as particles . this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level . bohr was the first to recognize this by incorporating the idea of quantization into the electronic structure of the hydrogen atom , and he was able to thereby explain the emission spectra of hydrogen as well as other one-electron systems .
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when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color . the emitted light can be refracted by a prism , producing spectra with a distinctive striped appearance due to the emission of certain wavelengths of light . for the relatively simple case of the hydrogen atom , the wavelengths of some emission lines could even be fitted to mathematical equations .
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is the the number of photons in the beam of light ?
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged . one of the founders of this field was danish physicist niels bohr , who was interested in explaining the discrete line spectrum observed when light was emitted by different elements . bohr was also interested in the structure of the atom , which was a topic of much debate at the time . numerous models of the atom had been postulated based on experimental results including the discovery of the electron by j. j. thomson and the discovery of the nucleus by ernest rutherford . bohr supported the planetary model , in which electrons revolved around a positively charged nucleus like the rings around saturn—or alternatively , the planets around the sun . however , scientists still had many unanswered questions : $ $ where are the electrons , and what are they doing ? if the electrons are orbiting the nucleus , why don ’ t they fall into the nucleus as predicted by classical physics ? how is the internal structure of the atom related to the discrete emission lines produced by excited elements ? bohr addressed these questions using a seemingly simple assumption : what if some aspects of atomic structure , such as electron orbits and energies , could only take on certain values ? quantization and photons by the early 1900s , scientists were aware that some phenomena occurred in a discrete , as opposed to continuous , manner . physicists max planck and albert einstein had recently theorized that electromagnetic radiation not only behaves like a wave , but also sometimes like particles called photons . planck studied the electromagnetic radiation emitted by heated objects , and he proposed that the emitted electromagnetic radiation was `` quantized '' since the energy of light could only have values given by the following equation : $ e_ { \text { photon } } =nh\nu $ , where $ n $ is a positive integer , $ h $ is planck ’ s constant— $ 6.626 \times10^ { -34 } \ , \text { j } \cdot \text s $ —and $ \nu $ is the frequency of the light , which has units of $ \dfrac { 1 } { \text s } $ . as a consequence , the emitted electromagnetic radiation must have energies that are multiples of $ h\nu $ . einstein used planck 's results to explain why a minimum frequency of light was required to eject electrons from a metal surface in the photoelectric effect . when something is quantized , it means that only specific values are allowed , such as when playing a piano . since each key of a piano is tuned to a specific note , only a certain set of notes—which correspond to frequencies of sound waves—can be produced . as long as your piano is properly tuned , you can play an f or f sharp , but you ca n't play the note that is halfway between an f and f sharp . atomic line spectra atomic line spectra are another example of quantization . when an element or ion is heated by a flame or excited by electric current , the excited atoms emit light of a characteristic color . the emitted light can be refracted by a prism , producing spectra with a distinctive striped appearance due to the emission of certain wavelengths of light . for the relatively simple case of the hydrogen atom , the wavelengths of some emission lines could even be fitted to mathematical equations . the equations did not explain why the hydrogen atom emitted those particular wavelengths of light , however . prior to bohr 's model of the hydrogen atom , scientists were unclear of the reason behind the quantization of atomic emission spectra . bohr 's model of the hydrogen atom : quantization of electronic structure bohr ’ s model of the hydrogen atom started from the planetary model , but he added one assumption regarding the electrons . what if the electronic structure of the atom was quantized ? bohr suggested that perhaps the electrons could only orbit the nucleus in specific orbits or shells with a fixed radius . only shells with a radius given by the equation below would be allowed , and the electron could not exist in between these shells . mathematically , we could write the allowed values of the atomic radius as $ r ( n ) =n^2\cdot r ( 1 ) $ , where $ n $ is a positive integer , and $ r ( 1 ) $ is the bohr radius , the smallest allowed radius for hydrogen . he found that $ r ( 1 ) $ has the value $ \text { bohr radius } =r ( 1 ) =0.529 \times 10^ { -10 } \ , \text { m } $ by keeping the electrons in circular , quantized orbits around the positively-charged nucleus , bohr was able to calculate the energy of an electron in the $ n $ th energy level of hydrogen : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ , where the lowest possible energy or ground state energy of a hydrogen electron— $ e ( 1 ) $ —is $ -13.6\ , \text { ev } $ . note that the energy is always going to be a negative number , and the ground state , $ n=1 $ , has the most negative value . this is because the energy of an electron in orbit is relative to the energy of an electron that has been completely separated from its nucleus , $ n=\infty $ , which is defined to have an energy of $ 0\ , \text { ev } $ . since an electron in orbit around the nucleus is more stable than an electron that is infinitely far away from its nucleus , the energy of an electron in orbit is always negative . absorption and emission bohr could now precisely describe the processes of absorption and emission in terms of electronic structure . according to bohr 's model , an electron would absorb energy in the form of photons to get excited to a higher energy level as long as the photon 's energy was equal to the energy difference between the initial and final energy levels . after jumping to the higher energy level—also called the excited state—the excited electron would be in a less stable position , so it would quickly emit a photon to relax back to a lower , more stable energy level . the energy levels and transitions between them can be illustrated using an energy level diagram , such as the example above showing electrons relaxing back to the $ n=2 $ level of hydrogen . the energy of the emitted photon is equal to the difference in energy between the two energy levels for a particular transition . the energy difference between energy levels $ n_ { high } $ and $ n_ { low } $ can be calculated using the equation for $ e ( n ) $ from the previous section : $ \begin { align } \delta e & amp ; = e ( n_ { high } ) -e ( n_ { low } ) \ \ & amp ; =\left ( -\dfrac { 1 } { { n_ { high } } ^2 } \cdot 13.6\ , \text { ev } \right ) -\left ( -\dfrac { 1 } { { n_ { low } } ^2 } \cdot 13.6\ , \text { ev } \right ) \ \ & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } \end { align } $ since we also know the relationship between the energy of a photon and its frequency from planck 's equation , we can solve for the frequency of the emitted photon : $ \begin { align } h\nu & amp ; =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } ~~~~~~~~~~~~\text { set photon energy equal to energy difference } \ \ \nu & amp ; = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~~~~~~~~~\text { solve for frequency } \end { align } $ we can also find the equation for the wavelenth of the emitted electromagnetic radiation using the relationship between the speed of light $ \text c $ , frequency $ \nu $ , and wavelength $ \lambda $ : $ \begin { align } \text c & amp ; =\lambda \nu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { rearrange to solve for } \nu . \ \dfrac { \text c } { \lambda } & amp ; =\nu=\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h } ~~~~~~~~~~~~~~\text { divide both sides by c to solve for } \dfrac { 1 } { \lambda } .\ \ \dfrac { 1 } { \lambda } & amp ; =\left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot \dfrac { 13.6\ , \text { ev } } { h\text c } \end { align } $ thus , we can see that the frequency—and wavelength—of the emitted photon depends on the energies of the initial and final shells of an electron in hydrogen . what have we learned since bohr proposed his model of hydrogen ? the bohr model worked beautifully for explaining the hydrogen atom and other single electron systems such as $ \text { he } ^+ $ . unfortunately , it did not do as well when applied to the spectra of more complex atoms . furthermore , the bohr model had no way of explaining why some lines are more intense than others or why some spectral lines split into multiple lines in the presence of a magnetic field—the zeeman effect . in the following decades , work by scientists such as erwin schrödinger showed that electrons can be thought of as behaving like waves and behaving as particles . this means that it is not possible to know both a given electron ’ s position in space and its velocity at the same time , a concept that is more precisely stated in heisenberg 's uncertainty principle . the uncertainty principle contradicts bohr ’ s idea of electrons existing in specific orbits with a known velocity and radius . instead , we can only calculate probabilities of finding electrons in a particular region of space around the nucleus . the modern quantum mechanical model may sound like a huge leap from the bohr model , but the key idea is the same : classical physics is not sufficient to explain all phenomena on an atomic level . bohr was the first to recognize this by incorporating the idea of quantization into the electronic structure of the hydrogen atom , and he was able to thereby explain the emission spectra of hydrogen as well as other one-electron systems .
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key points bohr 's model of hydrogen is based on the nonclassical assumption that electrons travel in specific shells , or orbits , around the nucleus . bohr 's model calculated the following energies for an electron in the shell , $ n $ : $ e ( n ) =-\dfrac { 1 } { n^2 } \cdot 13.6\ , \text { ev } $ bohr explained the hydrogen spectrum in terms of electrons absorbing and emitting photons to change energy levels , where the photon energy is $ h\nu =\delta e = \left ( \dfrac { 1 } { { n_ { low } } ^2 } -\dfrac { 1 } { { n_ { high } } ^2 } \right ) \cdot 13.6\ , \text { ev } $ bohr 's model does not work for systems with more than one electron . the planetary model of the atom at the beginning of the 20th century , a new field of study known as quantum mechanics emerged .
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what does the unit ev stand for ?
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