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In July 2021, Microsoft announced it will start selling subscriptions to virtualized Windows desktops as part of a new "Windows 365" service in the following month. It is not a standalone version of Windows, but a web service that provides access to Windows 10 and Windows 11 built on top of Azure Virtual Desktop. The n... | https://en.wikipedia.org/wiki?curid=18890 |
Interface languages for the operating system are free for download, but some languages are limited to certain editions of Windows. Language Interface Packs (LIPs) are redistributable and may be downloaded from Microsoft's Download Center and installed for any edition of Windows (XP or later) they translate most, but no... | https://en.wikipedia.org/wiki?curid=18890 |
Windows 8 and Windows Server 2012 introduces a new Language Control Panel where both the interface and input languages can be simultaneously changed, and language packs, regardless of type, can be downloaded from a central location. The PC Settings app in Windows 8.1 and Windows Server 2012 R2 also includes a counterpa... | https://en.wikipedia.org/wiki?curid=18890 |
Including personal computers of all kinds (e.g., desktops, laptops, mobile devices, and game consoles), Windows OSes accounted for 32.67% of usage share in August 2021, compared to Android (highest, at 46.03%), iOS's 13.76%, iPadOS's 2.81%, and macOS's 2.51%, according to Net Applications and 30.73% of usage share in A... | https://en.wikipedia.org/wiki?curid=18890 |
While the Windows 9x series offered the option of having profiles for multiple users, it had no concept of access privileges, allowing any user to edit others' files. In addition, while it ran separate 32-bit applications in separate address spaces, protecting an application's code and data from being read or written b... | https://en.wikipedia.org/wiki?curid=18890 |
Windows NT was far more secure, implementing access privileges and full memory protection, and, while 32-bit programs meeting the DoD's C2 security rating, yet these advantages were nullified by the fact that, prior to Windows Vista, the default user account created during the setup process was an administrator account... | https://en.wikipedia.org/wiki?curid=18890 |
Windows Vista introduced a privilege elevation system called User Account Control. When logging in as a standard user, a logon session is created and a token containing only the most basic privileges is assigned. In this way, the new logon session is incapable of making changes that would affect the entire system. When... | https://en.wikipedia.org/wiki?curid=18890 |
In August 2019, computer experts reported that the BlueKeep security vulnerability, , that potentially affects older unpatched Windows versions via the program's Remote Desktop Protocol, allowing for the possibility of remote code execution, may now include related flaws, collectively named "DejaBlue", affecting newer ... | https://en.wikipedia.org/wiki?curid=18890 |
All Windows versions from Windows NT 3 have been based on a file system permission system referred to as AGDLP(Accounts, Global, Domain Local, Permissions) in which file permissions are applied to the file/folder in the form of a 'local group' which then has other 'global groups' as members. These global groups then ho... | https://en.wikipedia.org/wiki?curid=18890 |
Wikis are enabled by wiki software, otherwise known as wiki engines. A wiki engine, being a form of a content management system, differs from other web-based systems such as blog software, in that the content is created without any defined owner or leader, and wikis have little inherent structure, allowing structure to... | https://en.wikipedia.org/wiki?curid=32851 |
A wiki enables communities of editors and contributors to write documents collaboratively. All that people require to contribute is a computer, Internet access, a web browser, and a basic understanding of a simple markup language (e.g. MediaWiki markup language). A single page in a wiki website is referred to as a "wik... | https://en.wikipedia.org/wiki?curid=32851 |
Some wikis have an edit button or link directly on the page being viewed if the user has permission to edit the page. This can lead to a text-based editing page where participants can structure and format wiki pages with a simplified markup language, sometimes known as wikitext, wiki markup or wikicode (it can also lea... | https://en.wikipedia.org/wiki?curid=32851 |
Wikis can also make WYSIWYG editing available to users, usually through a JavaScript control that translates graphically entered formatting instructions into the corresponding HTML tags or wikitext. In those implementations, the markup of a newly edited, marked-up version of the page is generated and submitted to the s... | https://en.wikipedia.org/wiki?curid=32851 |
Many wiki implementations, such as MediaWiki, the software that powers Wikipedia, allow users to supply an "edit summary" when they edit a page. This is a short piece of text summarizing the changes they have made (e.g. "Corrected grammar" or "Fixed formatting in table"). It is not inserted into the article's main text... | https://en.wikipedia.org/wiki?curid=32851 |
Within the text of most pages, there are usually many hypertext links to other pages within the wiki. This form of non-linear navigation is more "native" to a wiki than structured/formalized navigation schemes. Users can also create any number of index or table-of-contents pages, with hierarchical categorization or wha... | https://en.wikipedia.org/wiki?curid=32851 |
Links are created using a specific syntax, the so-called "link pattern". Originally, most wikis used CamelCase to name pages and create links. These are produced by capitalizing words in a phrase and removing the spaces between them (the word "CamelCase" is itself an example). While CamelCase makes linking easy, it als... | https://en.wikipedia.org/wiki?curid=32851 |
Wikipedia became the most famous wiki site, launched in January 2001 and entering the top ten most popular websites in 2007. In the early 2000s (decade), wikis were increasingly adopted in enterprise as collaborative software. Common uses included project communication, intranets, and documentation, initially for techn... | https://en.wikipedia.org/wiki?curid=32851 |
In the late 1990s and early 2000s, the word "wiki" was used to refer to both user-editable websites and the software that powers them; the latter definition is still occasionally in use. Wiki inventor Ward Cunningham wrote in 2014 that the word "wiki" should not be used to refer to a single website, but rather to a mas... | https://en.wikipedia.org/wiki?curid=32851 |
Wikis are generally designed with the philosophy of making it easy to correct mistakes, rather than making it difficult to make them. Thus, while wikis are very open, they provide a means to verify the validity of recent additions to the body of pages. The most prominent, on almost every wiki, is the "Recent Changes" p... | https://en.wikipedia.org/wiki?curid=32851 |
In case unacceptable edits are missed on the "recent changes" page, some wiki engines provide additional content control. It can be monitored to ensure that a page, or a set of pages, keeps its quality. A person willing to maintain pages will be warned of modifications to the pages, allowing them to verify the validity... | https://en.wikipedia.org/wiki?curid=32851 |
Critics of publicly editable wiki systems argue that these systems could be easily tampered with by malicious individuals ("vandals") or even by well-meaning but unskilled users who introduce errors into the content, while proponents maintain that the community of users can catch such malicious or erroneous content and... | https://en.wikipedia.org/wiki?curid=32851 |
Wikis tend to take a "soft-security" approach to the problem of vandalism, making damage easy to undo rather than attempting to prevent damage. Larger wikis often employ sophisticated methods, such as bots that automatically identify and revert vandalism and JavaScript enhancements that show characters that have been a... | https://en.wikipedia.org/wiki?curid=32851 |
Edit wars can also occur as users repetitively revert a page to the version they favor. In some cases, editors with opposing views of which content should appear or what formatting style should be used will change and re-change each other's edits. This results in the page being "unstable" from a general user's perspect... | https://en.wikipedia.org/wiki?curid=32851 |
The English Wikipedia has the largest user base among wikis on the World Wide Web and ranks in the top 10 among all Web sites in terms of traffic. Other large wikis include the WikiWikiWeb, Memory Alpha, Wikivoyage, and Susning.nu, a Swedish-language knowledge base. Medical and health-related wiki examples include Ganf... | https://en.wikipedia.org/wiki?curid=32851 |
In 2005, the Gartner Group, noting the increasing popularity of wikis, estimated that they would become mainstream collaboration tools in at least 50% of companies by 2009. Wikis can be used for project management. Wikis have also been used in the academic community for sharing and dissemination of information across i... | https://en.wikipedia.org/wiki?curid=32851 |
Wikis have found some use within the legal profession and within the government. Examples include the Central Intelligence Agency's Intellipedia, designed to share and collect intelligence, DKospedia, which was used by the American Civil Liberties Union to assist with review of documents about the internment of detaine... | https://en.wikipedia.org/wiki?curid=32851 |
A city wiki (or local wiki) is a wiki used as a knowledge base and social network for a specific geographical locale. The term 'city wiki' or its foreign language equivalent (e.g. German 'Stadtwiki') is sometimes also used for wikis that cover not just a city, but a small town or an entire region. A city wiki contains ... | https://en.wikipedia.org/wiki?curid=32851 |
Joint authorship of articles, in which different users participate in correcting, editing, and compiling the finished product, can also cause editors to become tenants in common of the copyright, making it impossible to republish without permission of all co-owners, some of whose identities may be unknown due to pseudo... | https://en.wikipedia.org/wiki?curid=32851 |
Wikis and their users can be held liable for certain activities that occur on the wiki. If a wiki owner displays indifference and forgoes controls (such as banning copyright infringers) that he could have exercised to stop copyright infringement, he may be deemed to have authorized infringement, especially if the wiki ... | https://en.wikipedia.org/wiki?curid=32851 |
Sexual reproduction is a process exclusive to eukaryotes in which organisms produce offspring that possess a selection of the genetic traits of each parent. Genetic traits are contained within the deoxyribonucleic acid (DNA) of chromosomes. The cells of eukaryotes have a set of paired homologous chromosomes, one from e... | https://en.wikipedia.org/wiki?curid=26805 |
In animals, the haploid stage only occurs in the gametes, the haploid cells that are specialized to fuse to form a zygote that develops into a new diploid organism. In plants, the diploid organism produces haploid spores by meiosis that are capable of undergoing repeated cell division to produce multicellular haploid o... | https://en.wikipedia.org/wiki?curid=26805 |
In most birds, both excretion and reproduction is done through a single posterior opening, called the cloaca—male and female birds touch cloaca to transfer sperm, a process called "cloacal kissing". In many other terrestrial animals, males use specialized sex organs to assist the transport of sperm—these male sex organ... | https://en.wikipedia.org/wiki?curid=26805 |
The flowers of flowering plants contain their sexual organs. Flowers are usually hermaphroditic, containing both male and female sexual organs. The female parts, in the center of a flower, are the pistils, each unit consisting of a carpel, a style and a stigma. Two or more of these reproductive units may be merged to f... | https://en.wikipedia.org/wiki?curid=26805 |
The biological cause of an organism developing into one sex or the other is called "sex determination". The cause may be genetic, environmental, haplodiploidy, or multiple factors. Within animals and other organisms that have genetic sex-determination systems, the determining factor may be the presence of a sex chromos... | https://en.wikipedia.org/wiki?curid=26805 |
Humans and most other mammals have an XY sex-determination system: the Y chromosome carries factors responsible for triggering male development, making XY sex determination mostly based on the presence or absence of the Y chromosome. It is the male gamete that determines the sex of the offspring. In this system XX mamm... | https://en.wikipedia.org/wiki?curid=26805 |
In many animals and some plants, individuals of male and female sex differ in size and appearance, a phenomenon called sexual dimorphism. Sexual dimorphism in animals is often associated with sexual selection—the mating competition between individuals of one sex vis-à-vis the opposite sex. In many cases, the male of a ... | https://en.wikipedia.org/wiki?curid=26805 |
The table is divided into four roughly rectangular areas called blocks. The rows of the table are called periods, and the columns are called groups. Elements from the same group of the periodic table show similar chemical characteristics. Trends run through the periodic table, with nonmetallic character (keeping their ... | https://en.wikipedia.org/wiki?curid=23053 |
The first periodic table to become generally accepted was that of the Russian chemist Dmitri Mendeleev in 1869: he formulated the periodic law as a dependence of chemical properties on atomic mass. Because not all elements were then known, there were gaps in his periodic table, and Mendeleev successfully used the perio... | https://en.wikipedia.org/wiki?curid=23053 |
The periodic table continues to evolve with the progress of science. In nature, only elements up to atomic number 94 exist; to go further, it was necessary to synthesise new elements in the laboratory. Today, all the first 118 elements are known, completing the first seven rows of the table, but chemical characterisati... | https://en.wikipedia.org/wiki?curid=23053 |
Atoms can be subdivided into different types based on the number of protons (and thus also electrons) they have. This is called the atomic number, often symbolised "Z" (for "Zahl" — German for "number"). Each distinct atomic number therefore corresponds to a class of atom: these classes are called the chemical elements... | https://en.wikipedia.org/wiki?curid=23053 |
Today, 118 elements are known, the first 94 of which are known to occur naturally on Earth at present. Of the 94 natural elements, eighty have a stable isotope and one more (bismuth) has an almost-stable isotope (with a half-life over a billion times the age of the universe). Two more, thorium and uranium, have isotope... | https://en.wikipedia.org/wiki?curid=23053 |
An electron can be thought of as inhabiting an atomic orbital, which characterises the probability it can be found in any particular region of the atom. Their energies are quantised, which is to say that they can only take discrete values. Furthermore, electrons obey the Pauli exclusion principle: different electrons m... | https://en.wikipedia.org/wiki?curid=23053 |
Elements are known with up to the first seven shells occupied. The first shell contains only one orbital, a spherical s orbital. As it is in the first shell, this is called the 1s orbital. This can hold up to two electrons. The second shell similarly contains a 2s orbital, and it also contains three dumbbell-shaped 2p ... | https://en.wikipedia.org/wiki?curid=23053 |
Here the sign ≪ means "much less than" as opposed to < meaning just "less than". Phrased differently, electrons enter orbitals in order of increasing "n" + ℓ, and if two orbitals are available with the same value of "n" + ℓ, the one with lower "n" is occupied first. In general, orbitals with the same value of "n" + ℓ a... | https://en.wikipedia.org/wiki?curid=23053 |
Starting from the third element, lithium, the first shell is full, so its third electron occupies a 2s orbital, giving a 1s 2s configuration. The 2s electron is lithium's only valence electron, as the 1s subshell is now too tightly bound to the nucleus to participate in chemical bonding to other atoms. Thus the filled ... | https://en.wikipedia.org/wiki?curid=23053 |
Starting from element 11, sodium, the second shell is full, making the second shell a core shell for this and all heavier elements. The eleventh electron begins the filling of the third shell by occupying a 3s orbital, giving a configuration of 1s 2s 2p 3s for sodium. This configuration is abbreviated [Ne] 3s, where [N... | https://en.wikipedia.org/wiki?curid=23053 |
The first eighteen elements can thus be arranged as the start of a periodic table. Elements in the same column have the same number of valence electrons and have analogous valence electron configurations: these columns are called groups. The single exception is helium, which has two valence electrons like beryllium and... | https://en.wikipedia.org/wiki?curid=23053 |
Starting the next row, for potassium and calcium the 4s subshell is the lowest in energy, and therefore they fill it. Potassium adds one electron to the 4s shell ([Ar] 4s), and calcium then completes it ([Ar] 4s). However, starting from scandium ([Ar] 3d 4s) the 3d subshell becomes the next highest in energy. The 4s an... | https://en.wikipedia.org/wiki?curid=23053 |
At zinc ([Ar] 3d 4s), the 3d orbitals are completely filled with a total of ten electrons. Next come the 4p orbitals, completing the row, which are filled progressively by gallium ([Ar] 3d 4s 4p) through krypton ([Ar] 3d 4s 4p), in a manner analogous to the previous p-block elements. From gallium onwards, the 3d orbita... | https://en.wikipedia.org/wiki?curid=23053 |
The sixth row of the table likewise starts with two s-block elements: caesium and barium. After this, the first f-block elements (coloured green below) begin to appear, starting with lanthanum. These are sometimes termed inner transition elements. As there are now not only 4f but also 5d and 6s subshells at similar ene... | https://en.wikipedia.org/wiki?curid=23053 |
The seventh row is analogous to the sixth row: 7s fills (francium and radium), then 5f (actinium to nobelium), then 6d (lawrencium to copernicium), and finally 7p (nihonium to oganesson). Starting from lawrencium the 5f orbitals are in the core, and probably the 6d orbitals join the core starting from nihonium. Again t... | https://en.wikipedia.org/wiki?curid=23053 |
Under an international naming convention, the groups are numbered numerically from 1 to 18 from the leftmost column (the alkali metals) to the rightmost column (the noble gases). The f-block groups are ignored in this numbering. Groups can also be named by their first element, e.g. the "scandium group" for group 3. Pre... | https://en.wikipedia.org/wiki?curid=23053 |
Atomic radii (the size of atoms) are dependent on the sizes of their outermost orbitals. They generally decrease going left to right along the main-group elements, because the nuclear charge increases but the outer electrons are still in the same shell. However, going down a column, the radii generally increase, becaus... | https://en.wikipedia.org/wiki?curid=23053 |
In the transition elements, an inner shell is filling, but the size of the atom is still determined by the outer electrons. The increasing nuclear charge across the series and the increased number of inner electrons for shielding somewhat compensate each other, so the decrease in radius is smaller. The 4p and 5d atoms,... | https://en.wikipedia.org/wiki?curid=23053 |
Thallium and lead atoms are about the same size as indium and tin atoms respectively, but from bismuth to radon the 6p atoms are larger than the analogous 5p atoms. This happens because when atomic nuclei become highly charged, special relativity becomes needed to gauge the effect of the nucleus on the electron cloud. ... | https://en.wikipedia.org/wiki?curid=23053 |
The first ionisation energy of an atom is the energy required to remove an electron from it. This varies with the atomic radius: ionisation energy increases left to right and down to up, because electrons that are closer to the nucleus are held more tightly and are more difficult to remove. Ionisation energy thus is mi... | https://en.wikipedia.org/wiki?curid=23053 |
The valence of an element can be defined either as the number of hydrogen atoms that can combine with it to form a simple binary hydride, or as twice the number of oxygen atoms that can combine with it to form a simple binary oxide (that is, not a peroxide or a superoxide). The valences of the main-group elements are d... | https://en.wikipedia.org/wiki?curid=23053 |
The electron configuration suggests a ready explanation from the number of electrons available for bonding, although a full explanation requires considering the energy that would be released in forming compounds with different valences rather than simply considering electron configurations alone. For example, magnesium... | https://en.wikipedia.org/wiki?curid=23053 |
For transition metals, common oxidation states are nearly always at least +2 for similar reasons (uncovering the next subshell); this holds even for the metals with anomalous ds or ds configurations (except for silver), because repulsion between d-electrons means that the movement of the second electron from the s- to ... | https://en.wikipedia.org/wiki?curid=23053 |
As elements in the same group share the same valence configurations, they usually exhibit similar chemical behaviour. For example, the alkali metals in the first group all have one valence electron, and form a very homogeneous class of elements: they are all soft and reactive metals. However, there are many factors inv... | https://en.wikipedia.org/wiki?curid=23053 |
Another important property of elements is their electronegativity. Atoms can form covalent bonds to each other by sharing electrons in pairs, creating an overlap of valence orbitals. The degree to which each atom attracts the shared electron pair depends on the atom's electronegativity – the tendency of an atom towards... | https://en.wikipedia.org/wiki?curid=23053 |
A simple substance is a substance formed from atoms of one chemical element. The simple substances of the more electronegative atoms tend to share electrons (form covalent bonds) with each other. They form either small molecules (like hydrogen or oxygen, whose atoms bond in pairs) or giant structures stretching indefin... | https://en.wikipedia.org/wiki?curid=23053 |
The more electropositive atoms, however, tend to instead lose electrons, creating a "sea" of electrons engulfing cations. The outer orbitals of one atom overlap to share electrons with all its neighbours, creating a giant structure of molecular orbitals extending over all the atoms. This negatively charged "sea" pulls ... | https://en.wikipedia.org/wiki?curid=23053 |
The metallicity of an element can be predicted from electronic properties. When atomic orbitals overlap during metallic or covalent bonding, they create both bonding and antibonding molecular orbitals of equal capacity, with the antibonding orbitals of higher energy. Net bonding character occurs when there are more ele... | https://en.wikipedia.org/wiki?curid=23053 |
In group 14, both metallic and covalent bonding become possible. In a diamond crystal, covalent bonds between carbon atoms are strong, because they have a small atomic radius and thus the nucleus has more of a hold on the electrons. Therefore, the bonding orbitals that result are much lower in energy than the antibondi... | https://en.wikipedia.org/wiki?curid=23053 |
Elements in groups 15 through 17 have too many electrons to form giant covalent molecules that stretch in all three dimensions. For the lighter elements, the bonds in small diatomic molecules are so strong that a condensed phase is disfavoured: thus nitrogen (N), oxygen (O), white phosphorus (P), sulfur (S), and the st... | https://en.wikipedia.org/wiki?curid=23053 |
The dividing line between metals and nonmetals is roughly diagonal from top left to bottom right, with the transition series appearing to the left of this diagonal (as they have many available orbitals for overlap). This is expected, as metallicity tends to be correlated with electropositivity and the willingness to lo... | https://en.wikipedia.org/wiki?curid=23053 |
The following table considers the most stable allotropes at standard conditions. The elements coloured yellow form simple substances that are well-characterised by metallic bonding. Elements coloured light blue form giant covalent structures, whereas those coloured dark blue form small covalently bonded molecules that ... | https://en.wikipedia.org/wiki?curid=23053 |
Generally, metals are shiny and dense. They usually have high melting and boiling points due to the strength of the metallic bond, and are often malleable and ductile (easily stretched and shaped) because the atoms can move relative to each other without breaking the metallic bond. They conduct electricity because thei... | https://en.wikipedia.org/wiki?curid=23053 |
Nonmetals exhibit different properties. Those forming giant covalent crystals exhibit high melting and boiling points, as it takes considerable energy to overcome the strong covalent bonds. Those forming discrete molecules are held together mostly by dispersion forces, which are more easily overcome; thus they tend to ... | https://en.wikipedia.org/wiki?curid=23053 |
There are some other relationships throughout the periodic table between elements that are not in the same group, such as the diagonal relationships between elements that are diagonally adjacent (e.g. lithium and magnesium). Some similarities can also be found between the main groups and the transition metal groups, or... | https://en.wikipedia.org/wiki?curid=23053 |
Many other physical properties of the elements exhibit periodic variation in accordance with the periodic law, such as melting points, boiling points, heats of fusion, heats of vaporisation, atomisation energy, and so on. Similar periodic variations appear for the compounds of the elements, which can be observed by com... | https://en.wikipedia.org/wiki?curid=23053 |
Many terms have been used in the literature to describe sets of elements that behave similarly. The group names "alkali metal", "alkaline earth metal", "pnictogen", "chalcogen", "halogen", and "noble gas" are acknowledged by IUPAC; the other groups can be referred to by their number, or by their first element (e.g., gr... | https://en.wikipedia.org/wiki?curid=23053 |
The "lanthanides" are considered to be the elements La–Lu, which are all very similar to each other: historically they included only Ce–Lu, but lanthanum became included by common usage. The "rare earth elements" (or rare earth metals) add scandium and yttrium to the lanthanides. Analogously, the "actinides" are consid... | https://en.wikipedia.org/wiki?curid=23053 |
The scope of terms varies significantly between authors. For example, according to IUPAC, the noble gases extend to include the whole group, including the very radioactive superheavy element oganesson. However, among those who specialise in the superheavy elements, this is not often done: in this case "noble gas" is ty... | https://en.wikipedia.org/wiki?curid=23053 |
In 1817, German physicist Johann Wolfgang Döbereiner began to formulate one of the earliest attempts to classify the elements. In 1829, he found that he could form some of the elements into groups of three, with the members of each group having related properties. He termed these groups triads. Chlorine, bromine, and i... | https://en.wikipedia.org/wiki?curid=23053 |
German chemist Lothar Meyer noted the sequences of similar chemical and physical properties repeated at periodic intervals. According to him, if the atomic weights were plotted as ordinates (i.e. vertically) and the atomic volumes as abscissas (i.e. horizontally)—the curve obtained a series of maximums and minimums—the... | https://en.wikipedia.org/wiki?curid=23053 |
The definitive breakthrough came from the Russian chemist Dmitri Mendeleev. Although other chemists (including Meyer) had found some other versions of the periodic system at about the same time, Mendeleev was the most dedicated to developing and defending his system, and it was his system that most impacted the scienti... | https://en.wikipedia.org/wiki?curid=23053 |
In 1875, the French chemist Paul-Émile Lecoq de Boisbaudran, working without knowledge of Mendeleev's prediction, discovered a new element in a sample of the mineral sphalerite, and named it gallium. He isolated the element and began determining its properties. Mendeleev, reading de Boisbaudran's publication, sent a le... | https://en.wikipedia.org/wiki?curid=23053 |
The same year, English physicist Henry Moseley using X-ray spectroscopy confirmed van den Broek's proposal experimentally. Moseley determined the value of the nuclear charge of each element from aluminium to gold and showed that Mendeleev's ordering actually places the elements in sequential order by nuclear charge. Nu... | https://en.wikipedia.org/wiki?curid=23053 |
Bohr called his electron shells "rings" in 1913: atomic orbitals within shells did not exist at the time of his planetary model. Bohr explains in Part 3 of his famous 1913 paper that the maximum electrons in a shell is eight, writing, "We see, further, that a ring of n electrons cannot rotate in a single ring round a n... | https://en.wikipedia.org/wiki?curid=23053 |
The first one to systematically expand and correct the chemical potentials of Bohr's atomic theory was Walther Kossel in 1914 and in 1916. Kossel explained that in the periodic table new elements would be created as electrons were added to the outer shell. In Kossel's paper, he writes: "This leads to the conclusion tha... | https://en.wikipedia.org/wiki?curid=23053 |
Prompted by Bohr, Wolfgang Pauli took up the problem of electron configurations in 1923. Pauli extended Bohr's scheme to use four quantum numbers, and formulated his exclusion principle which stated that no two electrons could have the same four quantum numbers. This explained the lengths of the periods in the periodic... | https://en.wikipedia.org/wiki?curid=23053 |
The quantum theory clarified the transition metals and lanthanides as forming their own separate groups, transitional between the main groups, although some chemists had already proposed tables showing them this way before then: the English chemist Henry Bassett did so in 1892, the Danish chemist Julius Thomsen in 1895... | https://en.wikipedia.org/wiki?curid=23053 |
By 1936, the pool of missing elements from hydrogen to uranium had shrunk to four: elements 43, 61, 85, and 87 remained missing. Element 43 eventually became the first element to be synthesised artificially via nuclear reactions rather than discovered in nature. It was discovered in 1937 by Italian chemists Emilio Segr... | https://en.wikipedia.org/wiki?curid=23053 |
A significant controversy arose with elements 102 through 106 in the 1960s and 1970s, as competition arose between the LBNL team (now led by Albert Ghiorso) and a team of Soviet scientists at the Joint Institute for Nuclear Research (JINR) led by Georgy Flyorov. Each team claimed discovery, and in some cases each propo... | https://en.wikipedia.org/wiki?curid=23053 |
The TWG's criteria were used to arbitrate later element discovery claims from LBNL and JINR, as well as from research institutes in Germany (GSI) and Japan (Riken). Currently, consideration of discovery claims is performed by a IUPAC/IUPAP Joint Working Party. After priority was assigned, the elements were officially a... | https://en.wikipedia.org/wiki?curid=23053 |
In celebration of the periodic table's 150th anniversary, the United Nations declared the year 2019 as the International Year of the Periodic Table, celebrating "one of the most significant achievements in science". The discovery criteria set down by the TWG were updated in 2020 in response to experimental and theoreti... | https://en.wikipedia.org/wiki?curid=23053 |
Like the group 1 metals, hydrogen has one electron in its outermost shell and typically loses its only electron in chemical reactions. It has some metal-like chemical properties, being able to displace some metals from their salts. But hydrogen forms a diatomic nonmetallic gas at standard conditions, unlike the alkali ... | https://en.wikipedia.org/wiki?curid=23053 |
Helium is an unreactive noble gas at standard conditions, and has a full outer shell: these properties are like the noble gases in group 18, but not at all like the reactive alkaline earth metals of group 2. Therefore, helium is nearly universally placed in group 18 which its properties best match. However, helium only... | https://en.wikipedia.org/wiki?curid=23053 |
Published periodic tables show variation regarding the heavier members of group 3, which begins with scandium and yttrium. They are commonly lanthanum and actinium, but many physicists and chemists have argued that they should be lutetium and lawrencium. The spaces below yttrium are sometimes left blank as a third opti... | https://en.wikipedia.org/wiki?curid=23053 |
In 2015, a IUPAC project chaired by Eric Scerri was set up to decide the question, giving only Sc-Y-La-Ac and Sc-Y-Lu-Lr as possible resolutions. In 2021, it decided on Sc-Y-Lu-Lr on the basis of three "desiderata": displaying all elements in order of increasing atomic number, avoiding a split of the d-block into "two ... | https://en.wikipedia.org/wiki?curid=23053 |
The most recently named elements – nihonium (113), moscovium (115), tennessine (117), and oganesson (118) – completed the seventh row of the periodic table. Future elements would have to begin an eighth row. These elements may be referred to either by their atomic numbers (e.g. "element 119"), or by the IUPAC systemati... | https://en.wikipedia.org/wiki?curid=23053 |
Currently, discussion continues regarding whether this future eighth period should follow the pattern set by the earlier periods or not, as calculations predict that by this point relativistic effects should result in significant deviations from the Madelung rule. Various different models have been suggested. All agree... | https://en.wikipedia.org/wiki?curid=23053 |
Nuclear stability will likely prove a decisive factor constraining the number of possible elements. It depends on the balance between the electric repulsion between protons and the strong force binding protons and neutrons together. Protons and neutrons are arranged in shells, just like electrons, and so a closed shell... | https://en.wikipedia.org/wiki?curid=23053 |
The periodic law may be represented in multiple ways, of which the standard periodic table is only one. Within 100 years of the appearance of Mendeleev's table in 1869, Edward G. Mazurs had collected an estimated 700 different published versions of the periodic table. Many forms retain the rectangular structure, includ... | https://en.wikipedia.org/wiki?curid=23053 |
The many different forms of the periodic table have prompted the questions of whether there is an optimal or definitive form of the periodic table, and if so, what it might be. There are no current consensus answers to either question. Janet's left-step table is being increasingly discussed as a candidate for being the... | https://en.wikipedia.org/wiki?curid=23053 |
The various sub-fields of AI research are centered around particular goals and the use of particular tools. The traditional goals of AI research include reasoning, knowledge representation, planning, learning, natural language processing, perception, and the ability to move and manipulate objects. General intelligence ... | https://en.wikipedia.org/wiki?curid=1164 |
By the 1950s, two visions for how to achieve machine intelligence emerged. One vision, known as Symbolic AI or GOFAI, was to use computers to create a symbolic representation of the world and systems that could reason about the world. Proponents included Allen Newell, Herbert A. Simon, and Marvin Minsky. Closely associ... | https://en.wikipedia.org/wiki?curid=1164 |
Unsupervised learning finds patterns in a stream of input. Supervised learning requires a human to label the input data first, and comes in two main varieties: classification and numerical regression. Classification is used to determine what category something belongs in – the program sees a number of examples of thing... | https://en.wikipedia.org/wiki?curid=1164 |
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