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The male gamete, a spermatozoon (produced in vertebrates within the testes), is a small cell containing a single long flagellum which propels it. | https://en.wikipedia.org/wiki?curid=26805 |
Spermatozoa are extremely reduced cells, lacking many cellular components that would be necessary for embryonic development. They are specialized for motility, seeking out an egg cell and fusing with it in a process called fertilization. | https://en.wikipedia.org/wiki?curid=26805 |
Female gametes are egg cells. In vertebrates they are produced within the ovaries. They are large immobile cells that contain the nutrients and cellular components necessary for a developing embryo. Egg cells are often associated with other cells which support the development of the embryo, forming an egg. In mammals, ... | https://en.wikipedia.org/wiki?curid=26805 |
Animals are usually mobile and seek out a partner of the opposite sex for mating. Animals which live in the water can mate using external fertilization, where the eggs and sperm are released into and combine within the surrounding water. Most animals that live outside of water, however, use internal fertilization, tran... | 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 |
Because of their motility, animal sexual behavior can involve coercive sex. Traumatic insemination, for example, is used by some insect species to inseminate females through a wound in the abdominal cavity—a process detrimental to the female's health. | https://en.wikipedia.org/wiki?curid=26805 |
Like animals, land plants have specialized male and female gametes. In seed plants, male gametes are produced by reduced male gametophytes that are contained within hard coats, forming pollen. The female gametes of seed plants are contained within ovules. Once fertilized these form seeds which, like eggs, contain the n... | 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 |
Some hermaphroditic plants are self-fertile, but plants have evolved multiple different self-incompatibility mechanisms to avoid self-fertilization, involving sequential hermaphroditism, molecular recognition systems and morphological mechanisms such as heterostyly. | https://en.wikipedia.org/wiki?curid=26805 |
In pines and other conifers the sex organs are produced within cones that have male and female forms. Male cones are smaller than female ones and produce pollen which is transported by wind to land in female cones. The larger and longer-lived female cones are typically more durable, and contain ovules within them that ... | https://en.wikipedia.org/wiki?curid=26805 |
Because seed plants are immobile, they depend upon passive methods for transporting pollen grains to other plants. Many, including conifers and grasses, produce lightweight pollen which is carried by wind to neighboring plants. Some flowering plants have heavier, sticky pollen that is specialized for transportation by ... | https://en.wikipedia.org/wiki?curid=26805 |
Most fungi reproduce sexually and have both haploid and diploid stages in their life cycles. These fungi are typically isogamous, lacking male and female specialization: haploid fungi grow into contact with each other and then fuse their cells. In some of these cases, the fusion is asymmetric, and the cell which donate... | https://en.wikipedia.org/wiki?curid=26805 |
Some fungi, including baker's yeast, have mating types that create a duality similar to male and female roles. Yeast with the same mating type will not fuse with each other to form diploid cells, only with yeast carrying the other mating type. | https://en.wikipedia.org/wiki?curid=26805 |
Many species of higher fungi produce mushrooms as part of their sexual reproduction. Within the mushroom diploid cells are formed, later dividing into haploid spores. The height of the mushroom aids the dispersal of these sexually produced offspring. | https://en.wikipedia.org/wiki?curid=26805 |
Approximately 95% of animal species have separate male and female individuals, and are said to be gonochoric. About 5% of animal species are hermaphroditic. This low percentage is due to the very large number of insect species, in which hermaphroditism is absent. About 99% of vertebrates are gonochoric, and the remaini... | https://en.wikipedia.org/wiki?curid=26805 |
The majority of plants are bisexual, either hermaphrodite (with both stamens and pistil in the same flower) or monoecious. In dioecious species male and female sexes are on separate plants. About 5% of flowering plants are dioecious, resulting from as many as 5000 independent origins. Dioecy is common in gymnosperms, i... | https://en.wikipedia.org/wiki?curid=26805 |
It is generally accepted that isogamy was ancestral to anisogamy and that anisogamy evolved several times independently in different groups of eukaryotes, including protists, algae, plants, and animals. The evolution of anisogamy is synonymous with the origin of male and the origin of female. It is also the first step ... | https://en.wikipedia.org/wiki?curid=26805 |
However, the evolution of anisogamy has left no fossil evidence and until 2006 there was no genetic evidence for the evolutionary link between sexes and mating types. It is unclear whether anisogamy first led to the evolution of hermaphroditism or the evolution of gonochorism. | https://en.wikipedia.org/wiki?curid=26805 |
But a 1.2 billion year old fossil from "Bangiomorpha pubescens" has provided the oldest fossil record for the differentiation of male and female reproductive types and shown that sexes evolved early in eukaryotes. | https://en.wikipedia.org/wiki?curid=26805 |
The original form of sex was external fertilization. Internal fertilization, or sex as we know it, evolved later and became dominant for vertebrates after their emergence on land. | 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 |
Sex determination is often distinct from sex differentiation. Sex determination is the designation for the development stage towards either male or female while sex differentiation is the pathway towards the development of the phenotype. | 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 |
XY sex determination is found in other organisms, including insects like the common fruit fly, and some plants. In some cases, it is the number of X chromosomes that determines sex rather than the presence of a Y chromosome. In the fruit fly individuals with XY are male and individuals with XX are female; however, indi... | https://en.wikipedia.org/wiki?curid=26805 |
In birds, which have a ZW sex-determination system, the W chromosome carries factors responsible for female development, and default development is male. In this case, ZZ individuals are male and ZW are female. It is the female gamete that determines the sex of the offspring. This system is used by birds, some fish, an... | https://en.wikipedia.org/wiki?curid=26805 |
The majority of butterflies and moths also have a ZW sex-determination system. Females can have Z, ZZW, and even ZZWW. | https://en.wikipedia.org/wiki?curid=26805 |
In the X0 sex-determination system, males have one X chromosome (X0) while females have two (XX). All other chromosomes in these diploid organisms are paired, but organisms may inherit one or two X chromosomes. This system is found in most arachnids, insects such as silverfish (Apterygota), dragonflies (Paleoptera) and... | https://en.wikipedia.org/wiki?curid=26805 |
In field crickets, for example, insects with a single X chromosome develop as male, while those with two develop as female. | https://en.wikipedia.org/wiki?curid=26805 |
In the nematode "Caenorhabditis elegans", most worms are self-fertilizing hermaphrodites with an XX karyotype, but occasional abnormalities in chromosome inheritance can give rise to individuals with only one X chromosome—these X0 individuals are fertile males (and half their offspring are male). | https://en.wikipedia.org/wiki?curid=26805 |
In the Z0 sex-determination system, males have two Z chromosomes whereas females have one. This system is found in several species of moths. | https://en.wikipedia.org/wiki?curid=26805 |
For many species, sex is not determined by inherited traits, but instead by environmental factors such as temperature experienced during development or later in life. | https://en.wikipedia.org/wiki?curid=26805 |
In the fern "Ceratopteris" and other homosporous fern species, the default sex is hermaphrodite, but individuals which grow in soil that has previously supported hermaphrodites are influenced by the pheromone antheridiogen to develop as male. The bonelliidae larvae can only develop as males when they encounter a female... | https://en.wikipedia.org/wiki?curid=26805 |
Some species can change sex over the course of their lifespan, a phenomenon called sequential hermaphroditism. Teleost fishes are the only vertebrate lineage where sequential hermaphroditism occurs. In clownfish, smaller fish are male, and the dominant and largest fish in a group becomes female; when a dominant female ... | https://en.wikipedia.org/wiki?curid=26805 |
Many reptiles, including all crocodiles and most turtles, have temperature-dependent sex determination. In these species, the temperature experienced by the embryos during their development determines their sex. In some turtles, for example, males are produced at lower temperatures than females; but "Macroclemys" femal... | https://en.wikipedia.org/wiki?curid=26805 |
Other insects, including honey bees and ants, use a haplodiploid sex-determination system. Diploid bees and ants are generally female, and haploid individuals (which develop from unfertilized eggs) are male. This sex-determination system results in highly biased sex ratios, as the sex of offspring is determined by fert... | https://en.wikipedia.org/wiki?curid=26805 |
Anisogamy is the fundamental difference between male and female. Richard Dawkins has stated that it is possible to interpret all the differences between the sexes as stemming from this. | https://en.wikipedia.org/wiki?curid=26805 |
Sex differences in humans include a generally larger size and more body hair in men, while women have larger breasts, wider hips, and a higher body fat percentage. In other species, there may be differences in coloration or other features, and may be so pronounced that the different sexes may be mistaken for two entire... | 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 |
Females are the larger sex in a majority of animals. For instance, female southern black widow spiders are typically twice as long as the males. This size disparity may be associated with the cost of producing egg cells, which requires more nutrition than producing sperm: larger females are able to produce more eggs. | https://en.wikipedia.org/wiki?curid=26805 |
Sexual dimorphism can be extreme, with males, such as some anglerfish, living parasitically on the female. Some plant species also exhibit dimorphism in which the females are significantly larger than the males, such as in the moss genus "Dicranum" and the liverwort genus "Sphaerocarpos". There is some evidence that, i... | https://en.wikipedia.org/wiki?curid=26805 |
In birds, males often have a more colourful appearance and may have features (like the long tail of male peacocks) that would seem to put them at a disadvantage (e.g. bright colors would seem to make a bird more visible to predators). One proposed explanation for this is the handicap principle. This hypothesis argues t... | https://en.wikipedia.org/wiki?curid=26805 |
The sexes across gonochoric species usually differ in behavior. In most animal species females invest more in parental care, although in some species, such as some coucals, the males invest more parental care. Females also tend to be more choosy for who they mate with, such as most bird species. Males tend to be more c... | https://en.wikipedia.org/wiki?curid=26805 |
The periodic table, also known as the periodic table of the (chemical) elements, is a rows and columns arrangement of the chemical elements. It is widely used in chemistry, physics, and other sciences, and is generally seen as an icon of chemistry. It is a graphic formulation of the periodic law, which states that the ... | https://en.wikipedia.org/wiki?curid=23053 |
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 |
The periodic table is a 2-dimensional structured table. The elements are placed in table cells, in reading order of ascending "atomic number". The table columns are called "groups", the rows are called "periods". The breaks at the end of each period occur according to a repetition (or periodicity) of physical and chemi... | https://en.wikipedia.org/wiki?curid=23053 |
The smallest constituents of all normal matter are known as atoms. Atoms are extremely small, being about one ten-billionth of a meter across; thus their internal structure is governed by quantum mechanics. Atoms consist of a small positively charged nucleus, made of positively charged protons and uncharged neutrons, s... | 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 |
The periodic table is a graphic description of the periodic law, which states that the properties and atomic structures of the chemical elements are a periodic function of their atomic number. Elements are placed in the periodic table by their electron configurations, which exhibit periodic recurrences that explain the... | 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 |
The sequence in which the subshells are filled is given in most cases by the Aufbau principle, also known as the Madelung or Klechkovsky rule (after Erwin Madelung and Vsevolod Klechkovsky respectively). This rule was first observed empirically by Madelung, and Klechkovsky and later authors gave it theoretical justific... | 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 |
The overlaps get quite close at the point where the d-orbitals enter the picture, and the order can shift slightly with atomic number and atomic charge. | https://en.wikipedia.org/wiki?curid=23053 |
Starting from the simplest atom, this lets us build up the periodic table one at a time in order of atomic number, by considering the cases of single atoms. In hydrogen, there is only one electron, which must go in the lowest-energy orbital 1s. This electron configuration is written 1s, where the superscript indicates ... | 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 next eighteen elements fill the 5s orbitals (rubidium and strontium), then 4d (yttrium through cadmium, again with a few anomalies along the way), and then 5p (indium through xenon). Again, from indium onward the 4d orbitals are in the core. Hence the fifth row has the same structure as the fourth. | 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 |
The following table shows the electron configuration of a neutral gas-phase atom of each element. Different configurations can be favoured in different chemical environments. The main-group elements have entirely regular electron configurations; the transition and inner transition elements show twenty irregularities du... | 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 |
For reasons of space, the periodic table is commonly presented with the f-block elements cut out and positioned placed as a distinct part below the main body. It reduces the number of element columns from 32 to 18. | https://en.wikipedia.org/wiki?curid=23053 |
Both forms represent the same periodic table. The form with the f-block included in the main body is sometimes called the 32-column or long form; the form with the f-block cut out the 18-column or medium-long form. The 32-column form has the advantage of showing all elements in their correct sequence, but it has the di... | https://en.wikipedia.org/wiki?curid=23053 |
Periodic tables usually at least show the elements' symbols; many also provide supplementary information about the elements, either via colour-coding or as data in the cells. The above table shows the names and atomic numbers of the elements, and also their blocks, natural occurrences and standard atomic weights. For t... | https://en.wikipedia.org/wiki?curid=23053 |
As chemical reactions involve the valence electrons, elements with similar outer electron configurations may be expected to react similarly and form compounds with similar proportions of elements in them. Such elements are placed in the same group, and thus there tend to be clear similarities and trends in chemical beh... | https://en.wikipedia.org/wiki?curid=23053 |
Historically, the physical size of atoms was unknown until the early 20th century. The first calculated estimate of the atomic radius of hydrogen was published by physicist Artur Haas in 1910 to within an order of magnitude (a factor of 10) of the accepted value, the Bohr radius (~0.529 Å). In his model, Haas used a si... | 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 |
In the transition series, the outer electrons are preferentially lost even though the inner orbitals are filling. For example, in the 3d series, the 4s electrons are lost first even though the 3d orbitals are being filled. The shielding effect of adding an extra 3d electron approximately compensates the rise in nuclear... | https://en.wikipedia.org/wiki?curid=23053 |
As metal atoms tend to lose electrons in chemical reactions, ionisation energy is generally correlated with chemical reactivity, although there are other factors involved as well. | https://en.wikipedia.org/wiki?curid=23053 |
The opposite property to ionisation energy is the electron affinity, which is the energy released when adding an electron to the atom. A passing electron will be more readily attracted to an atom if it feels the pull of the nucleus more strongly, and especially if there is an available partially filled outer orbital th... | https://en.wikipedia.org/wiki?curid=23053 |
Some atoms, like the noble gases, have no electron affinity: they cannot form stable gas-phase anions. The noble gases, having high ionisation energies and no electron affinity, have little inclination towards gaining or losing electrons and are generally unreactive. | https://en.wikipedia.org/wiki?curid=23053 |
Some exceptions to the trends occur: oxygen and fluorine have lower electron affinities than their heavier homologues sulfur and chlorine, because they are small atoms and hence the newly added electron would experience significant repulsion from the already present ones. For the nonmetallic elements, electron affinity... | 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 |
Electronegativity depends on how strongly the nucleus can attract an electron pair, and so it exhibits a similar variation to the other properties already discussed: electronegativity tends to fall going up to down, and rise going left to right. The alkali and alkaline earth metals are among the most electropositive el... | https://en.wikipedia.org/wiki?curid=23053 |
Electronegativity is generally measured on the Pauling scale, on which the most electronegative reactive atom (fluorine) is given electronegativity 4.0, and the least electronegative atom (caesium) is given electronegativity 0.79. (Theoretically neon would be more electronegative than fluorine, but the Pauling scale ca... | https://en.wikipedia.org/wiki?curid=23053 |
An element's electronegativity varies with the identity and number of the atoms it is bonded to, as well as how many electrons it has already lost: an atom becomes more electronegative when it has lost more electrons. This sometimes makes a large difference: lead in the +2 oxidation state has electronegativity 1.87 on ... | 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 |
It is common to designate a class of metalloids straddling the boundary between metals and nonmetals, as elements in that region are intermediate in both physical and chemical properties. However, no consensus exists in the literature for precisely which elements should be so designated. When such a category is used, s... | 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 |
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