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chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structure, proper ...
, a nonmetal is a
chemical element A chemical element is a species of atoms that have a given number of protons in their atomic nucleus, nuclei, including the pure Chemical substance, substance consisting only of that species. Unlike chemical compounds, chemical elements canno ...
that generally lacks a predominance of
metal A metal (from ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, e ...
lic properties; they range from colorless gases (like
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...
) to shiny solids (like carbon, as
graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on la ...
). The
electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have n ...
s in nonmetals behave differently from those in metals. With some exceptions, those in nonmetals are fixed in place, resulting in nonmetals usually being poor conductors of heat and electricity and brittle or crumbly when solid. The electrons in metals are generally free moving and this is why metals are good conductors and most are easily flattened into sheets and drawn into wires. Nonmetal atoms tend to attract
electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have n ...
s in
chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking ...
s and to form
acid In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a se ...
ic compounds. Two nonmetals,
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...
and
helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic ta ...
,
make up Cosmetics are constituted mixtures of chemical compounds derived from either natural sources, or synthetically created ones. Cosmetics have various purposes. Those designed for personal care and skin care can be used to cleanse or protect ...
about 99% of ordinary
matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic part ...
in the
observable universe The observable universe is a ball-shaped region of the universe comprising all matter that can be observed from Earth or its space-based telescopes and exploratory probes at the present time, because the electromagnetic radiation from these ob ...
by mass. Five nonmetallic elements, hydrogen,
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...
,
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
,
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
and
silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ...
, largely make up the
Earth's crust Earth's crust is Earth's thin outer shell of rock, referring to less than 1% of Earth's radius and volume. It is the top component of the lithosphere, a division of Earth's layers that includes the crust and the upper part of the mantle. The ...
,
atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A ...
, oceans and biosphere. Most nonmetals have biological, technological or domestic roles or uses. Living organisms are composed almost entirely of the nonmetals hydrogen, oxygen, carbon, and nitrogen. Nearly all nonmetals have individual uses in medicine and
pharmaceutical A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy ( pharmacotherapy) is an important part of the medical field and ...
s; lighting and
laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The ...
s; and household items. While the term ''non-metallic'' dates from as far back as 1566, there is no widely agreed precise definition of a nonmetal. Some elements have a marked mixture of metallic and nonmetallic properties; which of these borderline cases are counted as nonmetals can vary depending on the classification criteria. Fourteen elements are effectively always recognized as nonmetals and up to about nine more are frequently to sometimes added, as shown in the
periodic table 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 ch ...
extract.


Definition and applicable elements

A nonmetal is a
chemical element A chemical element is a species of atoms that have a given number of protons in their atomic nucleus, nuclei, including the pure Chemical substance, substance consisting only of that species. Unlike chemical compounds, chemical elements canno ...
deemed to lack a preponderance of metallic properties such as luster, deformability, good thermal and electrical conductivity, and the capacity to form a basic (rather than acidic) oxide. Since there is no rigorous definition of a nonmetal, Godovikov & Nenasheva 2020, p. 4 Sanderson 1957, p. 229 some variation exists among sources as to which elements are classified as such. The decisions involved depend on which property or properties are regarded as most indicative of nonmetallic or metallic character. Kneen, Rogers & Simpson 1972, pp. 218–219 Although Steudel, in 2020, recognised twenty-three elements as nonmetals, any such list is open to challenge. Fourteen almost always recognized are
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...
,
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
,
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
, and
sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...
; the highly reactive halogens
fluorine Fluorine is a chemical element with the symbol F and atomic number 9. It is the lightest halogen and exists at standard conditions as a highly toxic, pale yellow diatomic gas. As the most electronegative reactive element, it is extremely reactiv ...
,
chlorine Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...
,
bromine Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table ( halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simi ...
, and
iodine Iodine is a chemical element with the Symbol (chemistry), symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , ...
; and the noble gases
helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic ta ...
, neon,
argon Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice a ...
,
krypton Krypton (from grc, κρυπτός, translit=kryptos 'the hidden one') is a chemical element with the symbol Kr and atomic number 36. It is a colorless, odorless, tasteless noble gas that occurs in trace amounts in the atmosphere and is of ...
,
xenon Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...
, and
radon Radon is a chemical element with the symbol Rn and atomic number 86. It is a radioactive, colourless, odourless, tasteless noble gas. It occurs naturally in minute quantities as an intermediate step in the normal radioactive decay chains th ...
(see e.g. Larrañaga et al). The authors recognized
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...
,
phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ea ...
and
selenium Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, ...
as nonmetals; Vernon had earlier reported that these three elements were instead sometimes counted as
metalloids A metalloid is a type of chemical element which has a preponderance of properties in between, or that are a mixture of, those of metals and nonmetals. There is no standard definition of a metalloid and no complete agreement on which elements are ...
. The elements commonly recognized as
metalloids A metalloid is a type of chemical element which has a preponderance of properties in between, or that are a mixture of, those of metals and nonmetals. There is no standard definition of a metalloid and no complete agreement on which elements are ...
namely
boron Boron is a chemical element with the symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the '' boron group'' it has t ...
;
silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ...
and
germanium Germanium is a chemical element with the symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid in the carbon group that is chemically similar to its group neighbors ...
;
arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, b ...
and
antimony Antimony is a chemical element with the symbol Sb (from la, stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient ti ...
; and
tellurium Tellurium is a chemical element with the symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionall ...
are sometimes counted as an intermediate class between the metals and the nonmetals when the criteria used to distinguish between metals and nonmetals are inconclusive. At other times they are counted as nonmetals in light of their nonmetallic chemistry. Of the 118 known elements no more than about 20% are regarded as nonmetals. The status of a few elements is less certain.
Astatine Astatine is a chemical element with the symbol At and atomic number 85. It is the rarest naturally occurring element in the Earth's crust, occurring only as the decay product of various heavier elements. All of astatine's isotopes are short-live ...
, the fifth halogen, is often ignored on account of its rarity and intense radioactivity; theory and experimental evidence suggest it is a metal. The superheavy elements
copernicium Copernicium is a synthetic chemical element with the symbol Cn and atomic number 112. Its known isotopes are extremely radioactive, and have only been created in a laboratory. The most stable known isotope, copernicium-285, has a half-life of ap ...
(''Z'' = 112),
flerovium Flerovium is a superheavy chemical element with symbol Fl and atomic number 114. It is an extremely radioactive synthetic element. It is named after the Flerov Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research in Dub ...
(114), and oganesson (118) may turn out to be nonmetals; their status has not been confirmed.


General properties


Physical

:''Physical properties apply to elements in their most stable forms in ambient conditions'' About half of nonmetallic elements are gases; most of the rest are shiny solids.
Bromine Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table ( halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simi ...
, the only liquid, is so volatile that it is usually topped by a layer of its fumes; sulfur is the only colored solid nonmetal. The fluid nonmetals have very low densities,
melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depen ...
s and
boiling point The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding env ...
s, and are poor conductors of
heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...
and
electricity Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as describe ...
. Kneen, Rogers & Simpson 1972, pp. 261–264 The solid elements have low densities, are brittle or crumbly with low mechanical and structural strength, and poor to good conductors. The internal structures and bonding arrangements of the nonmetals explain their differences in form. Those existing as discrete atoms (e.g. xenon) or molecules (e.g. oxygen, sulfur and bromine) have low melting and boiling points as they are held together by weak
London dispersion forces London dispersion forces (LDF, also known as dispersion forces, London forces, instantaneous dipole–induced dipole forces, fluctuating induced dipole bonds or loosely as van der Waals forces) are a type of intermolecular force acting between a ...
acting between their atoms or molecules. Many are gases at room temperature. Nonmetals that form giant structures, such as chains of up to 1,000 atoms (e.g. selenium), sheets (e.g. carbon) or 3D lattices (e.g. silicon), have higher melting and boiling points, as it takes more energy to overcome their stronger
covalent bond A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between ato ...
s, so they are all solids. Those closer to the left side of the periodic table, or further down a column, often have some weak metallic interactions between their molecules, chains, or layers, consistent with their proximity to the metals; this occurs in boron, carbon, phosphorus, arsenic, selenium, antimony, tellurium, and iodine. Nonmetallic elements are either shiny, colored, or colorless. For boron, graphitic carbon, silicon, black phosphorus, germanium, arsenic, selenium, antimony, tellurium and iodine, their structures feature varying degrees of delocalised electrons that scatter incoming visible light, resulting in a shiny appearance. The colored nonmetals (sulfur, fluorine, chlorine, bromine) absorb some colours (wavelengths) and transmit the complementary colours. For chlorine, its "familiar yellow-green colour...is due to a broad region of absorption in the violet and blue regions of the spectrum". For the colorless nonmetals (hydrogen, nitrogen, oxygen, and the noble gases) their electrons are held sufficiently strongly such that no absorption occurs in the visible part of the spectrum, and all visible light is transmitted. The electrical and thermal conductivities of nonmetals and the brittle nature of the solids are likewise related to their internal arrangements. Whereas good conductivity and plasticity (malleability, ductility) are ordinarily associated with the presence of free moving and uniformly distributed electrons in metals the electrons in nonmetals typically lack such mobility. Among the nonmetallic elements, good electrical and thermal conductivity occurs only in carbon, arsenic and antimony. Good thermal conductivity otherwise occurs only in boron, silicon, phosphorus, and germanium; such conductivity is transmitted though vibrations of the crystalline lattices of these elements. Moderate electrical conductivity occurs in boron, silicon, phosphorus, germanium, selenium, tellurium and iodine. Plasticity occurs in limited circumstances only in carbon, phosphorus, sulfur, and selenium. The physical differences between metals and nonmetals arise from internal and external atomic forces. Internally, the
positive charge Electric charge is the physical property of matter that causes charged matter to experience a force when placed in an electromagnetic field. Electric charge can be ''positive'' or ''negative'' (commonly carried by protons and electrons resp ...
arising from the protons in an atom's nucleus acts to hold the atom's outer electrons in place. Externally, the same electrons are subject to attractive forces from the protons in nearby atoms. When the external forces are greater than, or equal to, the internal force, outer electrons are expected to become free to move between atoms, and metallic properties are predicted. Otherwise nonmetallic properties are expected.


Chemical

Nonmetals have moderate to high values of electronegativity and tend to form acidic compounds. For example, the solid nonmetals (including metalloids) react with
nitric acid Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available ni ...
to form either an acid, or an oxide that has acidic properties predominating. They tend to gain or share electrons when they react, unlike metals which tend to donate electrons. Given the stability of the
electron configuration In atomic physics and quantum chemistry, the electron configuration is the distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbitals. For example, the electron configuration of the neon ato ...
s of the noble gases (which have full outer shells), nonmetals generally gain enough electrons to give them the electron configuration of the following noble gas, whereas metals tend to lose electrons sufficient to leave them with the electron configuration of the preceding noble gas. For nonmetallic elements this tendency is summarized in the
duet A duet is a musical composition for two performers in which the performers have equal importance to the piece, often a composition involving two singers or two pianists. It differs from a harmony, as the performers take turns performing a sol ...
and
octet rule The octet rule is a chemical rule of thumb that reflects the theory that main-group elements tend to bond in such a way that each atom has eight electrons in its valence shell, giving it the same electronic configuration as a noble gas. The rul ...
s of thumb (and for metals there is a less rigorously predictive 18-electron rule). Nonmetals mostly have higher
ionization energies Ionization, or Ionisation is the process by which an atom or a molecule acquires a negative or positive charge by gaining or losing electrons, often in conjunction with other chemical changes. The resulting electrically charged atom or molecul ...
, electron affinities,
electronegativity Electronegativity, symbolized as , is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its atomic number and the ...
values, and
standard reduction potential Redox potential (also known as oxidation / reduction potential, ''ORP'', ''pe'', ''E_'', or E_) is a measure of the tendency of a chemical species to acquire electrons from or lose electrons to an electrode and thereby be reduced or oxidised respe ...
s than metals. In general, the higher these values the more nonmetallic is the element. The chemical differences between metals and nonmetals largely arise from the attractive force between the positive nuclear charge of an individual atom and its negatively charged outer electrons. From left to right across each period of the periodic table the nuclear charge increases as the number of
proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...
s in the
atomic nucleus The atomic nucleus is the small, dense region consisting of protons and neutrons at the center of an atom, discovered in 1911 by Ernest Rutherford based on the 1909 Geiger–Marsden gold foil experiment. After the discovery of the neutron ...
increases. There is an associated reduction in atomic radius as the increasing nuclear charge draws the outer electrons closer to the core. In metals, the effect of the nuclear charge is generally weaker than for nonmetallic elements. In bonding, metals therefore tend to lose electrons, and form positively charged or polarized atoms or ions whereas nonmetals tend to gain those same electrons due to their stronger nuclear charge, and form negatively charged ions or polarized atoms. The number of compounds formed by nonmetals is vast. The first ten places in a "top 20" table of elements most frequently encountered in 895,501,834 compounds, as listed in the
Chemical Abstracts Service CAS (formerly Chemical Abstracts Service) is a division of the American Chemical Society. It is a source of chemical information. CAS is located in Columbus, Ohio, United States. Print periodicals ''Chemical Abstracts'' is a periodical index th ...
register for November 2, 2021, were occupied by nonmetals. Hydrogen, carbon, oxygen and nitrogen were collectively found in the majority (80%) of compounds. Silicon, a metalloid, was in 11th place. The highest rated metal, with an occurrence frequency of 0.14%, was iron, in 12th place. A few examples of nonmetal compounds are:
boric acid Boric acid, more specifically orthoboric acid, is a compound of boron, oxygen, and hydrogen with formula . It may also be called hydrogen borate or boracic acid. It is usually encountered as colorless crystals or a white powder, that dissolve ...
(), used in ceramic glazes;
selenocysteine Selenocysteine (symbol Sec or U, in older publications also as Se-Cys) is the 21st proteinogenic amino acid. Selenoproteins contain selenocysteine residues. Selenocysteine is an analogue of the more common cysteine with selenium in place of the ...
(), the 21st
amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...
of life; phosphorus sesquisulfide (P4S3), in strike anywhere matches; and
teflon Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. It is one of the best-known and widely applied PFAS. The commonly known brand name of PTFE-based composition is Teflon by Chemo ...
()''n''), as used in non-stick coatings for pans and other cookware.


Complications

Complicating the chemistry of the nonmetals are the anomalies seen in the first row of each
periodic table block A block of the periodic table is a set of elements unified by the atomic orbitals their valence electrons or vacancies lie in. The term appears to have been first used by Charles Janet. Each block is named after its characteristic orbital: s-blo ...
. These anomalies are prominent in hydrogen, boron (whether as a nonmetal or metalloid), carbon, nitrogen, oxygen and fluorine. In later rows they manifest as secondary periodicity or non-uniform periodic trends going down most of the p-block groups, and unusual oxidation states in the heavier nonmetals.


First row anomaly

Starting with hydrogen, the first row anomaly largely arises from the electron configurations of the elements concerned. Hydrogen is noted for the different ways it forms bonds. It most commonly forms covalent bonds. It can lose its single electron in aqueous solution, leaving behind a bare proton with tremendous polarizing power. This consequently attaches itself to the lone electron pair of an oxygen atom in a water molecule, thereby forming the basis of acid-base chemistry. A hydrogen atom in a molecule can form a second, weaker, bond with an atom or group of atoms in another molecule. Such bonding, "helps give
snowflake A snowflake is a single ice crystal that has achieved a sufficient size, and may have amalgamated with others, which falls through the Earth's atmosphere as snow.Knight, C.; Knight, N. (1973). Snow crystals. Scientific American, vol. 228, no. ...
s their hexagonal symmetry, binds DNA into a
double helix A double is a look-alike or doppelgänger; one person or being that resembles another. Double, The Double or Dubble may also refer to: Film and television * Double (filmmaking), someone who substitutes for the credited actor of a character * ...
; shapes the three-dimensional forms of
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
s; and even raises water's boiling point high enough to make a decent cup of tea." Hydrogen and helium, and boron to neon have unusually small atomic radii. This occurs because the 1s and 2p subshells have no inner analogues (i.e., there is no zero shell and no 1p subshell) and they therefore experience no electron repulsion effects, unlike the 3p, 4p and 5p subshells of heavier elements. Siekierski & Burgess 2002, pp. 24–25 Ionization energies and electronegativities among these elements are consequently higher than would otherwise be expected, having regard to
periodic trends Periodic trends are specific patterns that are present in the periodic table that illustrate different aspects of a certain element. They were discovered by the Russian chemist Dmitri Mendeleev in the year 1863. Major periodic trends include atom ...
. The small atomic radii of carbon, nitrogen, and oxygen facilitate the formation of
double A double is a look-alike or doppelgänger; one person or being that resembles another. Double, The Double or Dubble may also refer to: Film and television * Double (filmmaking), someone who substitutes for the credited actor of a character * ...
or triple bonds. While it would normally be expected that hydrogen and helium, on electron configuration consistency grounds, would be located atop the s-block elements, the first row anomaly in these two elements is strong enough to warrant alternative placements. Hydrogen is occasionally positioned over fluorine, in group 17 rather than over lithium in group 1. Helium is regularly positioned over neon, in group 18, rather than over beryllium, in group 2.


Secondary periodicity

Immediately after the first row of d-block metals, scandium to zinc, the 3d electrons in the
p-block A block of the periodic table is a set of elements unified by the atomic orbitals their valence electrons or vacancies lie in. The term appears to have been first used by Charles Janet. Each block is named after its characteristic orbital: s-blo ...
elements i.e., gallium (a metal), germanium, arsenic, selenium, and bromine, are not as effective at shielding the increased positive nuclear charge. A similar effect accompanies the appearance of fourteen f-block metals between
barium Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element. Th ...
and lutetium, ultimately resulting in smaller than expected atomic radii for the elements from
hafnium Hafnium is a chemical element with the symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in many zirconium minerals. Its existence was predicted by Dmitri M ...
(Hf) onwards. The net result, especially for the group 13–15 elements, is that there is an alternation in some periodic trends going down groups 13 to 17.


Unusual oxidation states

The larger atomic radii of the heavier group 15–18 nonmetals enable higher bulk coordination numbers, and result in lower electronegativity values that better tolerate higher positive charges. The elements involved are thereby able to exhibit
oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...
s other than the lowest for their group (that is, 3, 2, 1, or 0) for example in
phosphorus pentachloride Phosphorus pentachloride is the chemical compound with the formula PCl5. It is one of the most important phosphorus chlorides, others being PCl3 and POCl3. PCl5 finds use as a chlorinating reagent. It is a colourless, water-sensitive and mois ...
(PCl5),
sulfur hexafluoride Sulfur hexafluoride or sulphur hexafluoride (British spelling) is an inorganic compound with the formula SF6. It is a colorless, odorless, non- flammable, and non-toxic gas. has an octahedral geometry, consisting of six fluorine atoms attach ...
(SF6),
iodine heptafluoride Iodine heptafluoride, also known as iodine(VII) fluoride or iodine fluoride, is an interhalogen compound with the chemical formula I F7. It has an unusual pentagonal bipyramidal structure, as predicted by VSEPR theory. The molecule can undergo ...
(IF7), and
xenon difluoride Xenon difluoride is a powerful fluorinating agent with the chemical formula , and one of the most stable xenon compounds. Like most covalent inorganic fluorides it is moisture-sensitive. It decomposes on contact with water vapor, but is otherwis ...
(XeF2).


Subclasses

Approaches to classifying nonmetals may involve from as few as two subclasses to up to six or seven. For example, the
Encyclopædia Britannica The (Latin for "British Encyclopædia") is a general knowledge English-language encyclopaedia. It is published by Encyclopædia Britannica, Inc.; the company has existed since the 18th century, although it has changed ownership various t ...
periodic table recognizes noble gases, halogens, and other nonmetals, and splits the elements commonly recognized as metalloids between "other metals" and "other nonmetals". The
Royal Society of Chemistry The Royal Society of Chemistry (RSC) is a learned society (professional association) in the United Kingdom with the goal of "advancing the chemical sciences". It was formed in 1980 from the amalgamation of the Chemical Society, the Royal Inst ...
periodic table instead uses a different color for each of its eight main groups, and nonmetals can be found in seven of these. From right to left in periodic table terms, three or four kinds of nonmetals are more or less commonly discerned. These are: *the relatively inert noble gases; *a set of chemically strong halogen elements—fluorine, chlorine, bromine and iodine—sometimes referred to as nonmetal halogens (the term used here) or stable halogens; *a set of unclassified nonmetals, including elements such as hydrogen, carbon, nitrogen, and oxygen, with no widely recognized collective name; and *the chemically weak nonmetallic metalloids Bailar et al. 1989, p. 742 sometimes considered to be nonmetals and sometimes not. Since the metalloids occupy "frontier territory", where metals meet nonmetals, their treatment varies from author to author. Some consider them separate from both metals and nonmetals; some regard them as nonmetals or as a sub-class of nonmetals. Other authors count some of them as metals, for example arsenic and antimony, due to their similarities to
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. Metalloids are here treated as nonmetals in light of their chemical behavior, and for comparative purposes. Aside from the metalloids, some boundary fuzziness and overlapping (as occurs with classification schemes generally) can be discerned among the other nonmetal subclasses. Carbon, phosphorus, selenium, iodine border the metalloids and show some metallic character, as does hydrogen. Among the noble gases, radon is the most metallic and begins to show some
cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
ic behavior, which is unusual for a nonmetal.


Noble gases

Six nonmetals are classified as noble gases:
helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic ta ...
, neon, argon, krypton,
xenon Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...
, and the radioactive radon. In conventional periodic tables they occupy the rightmost column. They are called ''noble gases'' in light of their characteristically very low
chemical reactivity In chemistry, reactivity is the impulse for which a chemical substance undergoes a chemical reaction, either by itself or with other materials, with an overall release of energy. ''Reactivity'' refers to: * the chemical reactions of a single su ...
. They have very similar properties, with all of them being colorless, odorless, and nonflammable. With their closed outer electron shells the noble gases have feeble interatomic forces of attraction resulting in very low melting and boiling points. That is why they are all gases under standard conditions, even those with
atomic mass The atomic mass (''m''a or ''m'') is the mass of an atom. Although the SI unit of mass is the kilogram (symbol: kg), atomic mass is often expressed in the non-SI unit dalton (symbol: Da) – equivalently, unified atomic mass unit (u). 1&n ...
es larger than many normally solid elements. Chemically, the noble gases have relatively high ionization energies, nil or negative electron affinities, and relatively high electronegativities. Compounds of the noble gases number in the hundreds although the list continues to grow, with most of these involving oxygen or fluorine combining with either krypton, xenon or radon. In periodic table terms, an analogy can be drawn between the
noble gas The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a class of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, monatomic gases with very low ch ...
es and
noble metal A noble metal is ordinarily regarded as a metallic chemical element that is generally resistant to corrosion and is usually found in nature in its raw form. Gold, platinum, and the other platinum group metals ( ruthenium, rhodium, palladium, o ...
s such as platinum and gold, with the latter being similarly reluctant to enter into chemical combination. As a further example, xenon, in the +8 oxidation state, forms a pale yellow explosive oxide, XeO4, while
osmium Osmium (from Greek grc, ὀσμή, osme, smell, label=none) is a chemical element with the symbol Os and atomic number 76. It is a hard, brittle, bluish-white transition metal in the platinum group that is found as a trace element in alloys, ...
, another noble metal, forms a yellow strongly oxidizing oxide, OsO4. There are parallels too in the formulas of the oxyfluorides: XeO2F4 and OsO2F4, and XeO3F2 and OsO3F2. About 1015 tonnes of noble gases are present in the Earth's atmosphere. Helium is additionally found in
natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbon d ...
to the extent of as much as 7%. Radon diffuses out of rocks, where it is formed during the natural decay sequence of
uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
and
thorium Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high ...
. In 2014 it was reported that the Earth's core may contain about 1013 tons of xenon, in the form of stable XeFe3 and XeNi3 intermetallic compounds. This may explain why "studies of the Earth's atmosphere have shown that more than 90% of the expected amount of Xe is depleted."


Nonmetal halogens

While the nonmetal halogens are markedly reactive and corrosive elements, they can be found in such mundane compounds as
toothpaste Toothpaste is a paste or gel dentifrice used with a toothbrush to clean and maintain the aesthetics and health of teeth. Toothpaste is used to promote oral hygiene: it is an abrasive that aids in removing dental plaque and food from the teeth, ...
( NaF); ordinary
table salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...
(NaCl); swimming pool disinfectant ( NaBr); or food supplements ( KI). The word "halogen" means "
salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...
former". Physically, fluorine and chlorine are pale yellow and yellowish green gases; bromine is a reddish-brown liquid (usually topped by a layer of its fumes); and iodine, under white light, is a metallic-looking solid. Electrically, the first three are insulators while iodine is a
semiconductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way ...
(along its planes). Greenwood & Earnshaw 2002, p. 804 Chemically, they have high ionization energies, electron affinities, and electronegativity values, and are mostly relatively strong
oxidizing agent An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ). In other words, an oxi ...
s. Manifestations of this status include their corrosive nature. Daniel & Rapp 1976, p. 55 All four exhibit a tendency to form predominately
ionic compound In chemistry, an ionic compound is a chemical compound composed of ions held together by electrostatic forces termed ionic bonding. The compound is neutral overall, but consists of positively charged ions called cations and negatively charged ...
s with metals Cotton et al. 1999, p. 554 whereas the remaining nonmetals, bar oxygen, tend to form predominately covalent compounds with metals. The reactive and strongly electronegative nature of the nonmetal halogens represents the epitome of nonmetallic character. Lanford 1959, p. 176 In periodic table terms, the counterparts of the highly nonmetallic halogens in group 17 are the highly reactive alkali metals, such as sodium and potassium, in group 1. Most of the alkali metals, as if in imitation of the nonmetal halogens, are known to form –1 anions (something that rarely occurs among metals). The nonmetal halogens are found in salt-related minerals. Fluorine occurs in
fluorite Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon. The Mohs sca ...
(CaF2), a widespread mineral. Chlorine, bromine and iodine are found in brines. Exceptionally, a 2012 study reported the presence of 0.04% native fluorine () by weight in
antozonite Antozonite (historically known as Stinkspat, Stinkfluss, Stinkstein, Stinkspar and fetid fluorite) is a radioactive fluorite variety first found in Wölsendorf, Bavaria, in 1841, and named in 1862. It is characterized by the presence of multip ...
, attributing these inclusions as a result of radiation from the presence of tiny amounts of
uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
.


Unclassified nonmetals

After the nonmetallic elements are classified as either noble gases, halogens or metalloids (following), the remaining seven nonmetals are hydrogen, carbon, nitrogen, oxygen, phosphorus, sulfur and selenium. In their most stable forms, three are colorless gases (H, N, O); three have a metal-like appearance (C, P, Se); and one is yellow (S). Electrically, graphitic carbon is a semimetal along its planes and a
semiconductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way ...
in a direction perpendicular to its planes; phosphorus and selenium are semiconductors; and hydrogen, nitrogen, oxygen, and sulfur are insulators. They are generally regarded as being too diverse to merit a collective examination, Cao et al. 2021, pp. 20–21 and have been referred to as ''other nonmetals'', or more plainly as ''nonmetals'', located between the ''metalloids'' and the ''halogens.'' Consequently, their chemistry tends to be taught disparately, according to their four respective periodic table groups, for example: hydrogen in group 1; the group 14 nonmetals (carbon, and possibly silicon and germanium); the group 15 nonmetals (nitrogen, phosphorus, and possibly arsenic and antimony); and the group 16 nonmetals (oxygen, sulfur, selenium, and possibly tellurium). Other subdivisions are possible according to the individual preferences of authors. Hydrogen, in particular, behaves in some respects like a metal and in others like a nonmetal. Like a metal it can (first) lose its single electron; it can stand in for alkali metals in typical alkali metal structures; and is capable of forming alloy-like
hydride In chemistry, a hydride is formally the anion of hydrogen( H−). The term is applied loosely. At one extreme, all compounds containing covalently bound H atoms are called hydrides: water (H2O) is a hydride of oxygen, ammonia is a hydride ...
s, featuring metallic bonding, with some
transition metal In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that can ...
s. Wiberg 2001, pp. 255–257 On the other hand, it is an insulating diatomic gas, like a typical nonmetal, and in chemical reactions has a tendency to eventually attain the electron configuration of helium. It does this by way of forming a covalent or ionic bond or, if it has lost its electron, attaching itself to a lone pair of electrons. Some or all of these nonmetals nevertheless have several shared properties. Most of them, being less reactive than the halogens, can occur naturally in the environment. They have prominent
biological Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary in ...
and
geochemical Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing the e ...
roles. While their physical and chemical character is "moderately non-metallic", on a net basis, all of them have corrosive aspects. Hydrogen can corrode metals. Carbon corrosion can occur in
fuel cell A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen fuel, hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most bat ...
s.
Acid rain Acid rain is rain or any other form of precipitation that is unusually acidic, meaning that it has elevated levels of hydrogen ions (low pH). Most water, including drinking water, has a neutral pH that exists between 6.5 and 8.5, but ac ...
is caused by dissolved nitrogen or sulfur. Oxygen corrodes iron via
rust Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO( ...
. White phosphorus, the most unstable form, ignites in air and produces
phosphoric acid Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solution, w ...
residue. Untreated selenium in soils can give rise to corrosive
hydrogen selenide Hydrogen selenide is an inorganic compound with the formula H2Se. This hydrogen chalcogenide is the simplest and most commonly encountered hydride of selenium. H2Se is a colorless, flammable gas under standard conditions. It is the most toxic sel ...
gas. When combined with metals, the unclassified nonmetals can form high
hardness In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. In general, different materials differ in their hardness; for example hard ...
(
interstitial An interstitial space or interstice is a space between structures or objects. In particular, interstitial may refer to: Biology * Interstitial cell tumor * Interstitial cell, any cell that lies between other cells * Interstitial collagenase ...
or
refractory In materials science, a refractory material or refractory is a material that is resistant to decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperatures. Refractories are polycrystalline, polyphase, ...
) compounds, on account of their relatively small atomic radii and sufficiently low ionization energy values. They show a tendency to bond to themselves, especially in solid compounds. Diagonal periodic table relationships among these nonmetals echo similar relationships among the metalloids. In periodic table terms, a geographic analogy is seen between the unclassified nonmetals and transition metals. The unclassified nonmetals occupy territory between the strongly nonmetallic halogens on the right and the weakly nonmetallic metalloids on the left. The transition metals occupy territory, "between the virulent and violent metals on the left of the periodic table, and the calm and contented metals to the right... nd.. form a transitional bridge between the two". Unclassified nonmetals typically occur in elemental forms (oxygen, sulfur) or are found in association with either of these two elements: Cox 1997, pp. 130–132; Emsley 2011, passim * Hydrogen occurs in the world's oceans as a component of water, and in
natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbon d ...
as a component of
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane ...
and
hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The under ...
. * Carbon occurs in limestone, dolomite, and marble, as carbonates. Less well known is carbon as graphite, which mainly occurs in
metamorphic Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...
silicate rocks as a result of the compression and heating of sedimentary carbon compounds. * Oxygen is found in the atmosphere; in the oceans as a component of water; and in the crust as
oxide mineral The oxide mineral class includes those minerals in which the oxide anion (O2−) is bonded to one or more metal alloys. The hydroxide-bearing minerals are typically included in the oxide class. The minerals with complex anion groups such as the ...
s. * Phosphorus minerals are widespread, usually as phosphorus-oxygen
phosphates In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phosph ...
. * Elemental sulfur can be found in or near hot springs and volcanic regions in many parts of the world; sulfur minerals are widespread, usually as
sulfides Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds la ...
or oxygen-sulfur sulfates. * Selenium occurs in metal sulfide ores, where it partially replaces the sulfur; elemental selenium is occasionally found.


Metalloids

The six elements more commonly recognized as metalloids are boron, silicon, germanium, arsenic, antimony, and tellurium, each having a metallic appearance. On a standard periodic table, they occupy a diagonal area in the p-block extending from boron at the upper left to tellurium at lower right, along the dividing line between metals and nonmetals shown on some tables. Vernon 2013 They are brittle and poor to good conductors of heat and electricity. Boron, silicon, germanium and tellurium are semiconductors. Arsenic and antimony have the electronic structures of semimetals although both have less stable semiconducting
forms Form is the shape, visual appearance, or configuration of an object. In a wider sense, the form is the way something happens. Form also refers to: *Form (document), a document (printed or electronic) with spaces in which to write or enter data * ...
. Chemically the metalloids generally behave like (weak) nonmetals. Among the nonmetallic elements they tend to have the lowest ionization energies, electron affinities, and electronegativity values, and are relatively weak oxidizing agents. They further demonstrate a tendency to form alloys with metals. In periodic table terms, to the left of the weakly nonmetallic metalloids are an indeterminate set of weakly metallic metals (such as tin,
lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, ...
and
bismuth Bismuth is a chemical element with the symbol Bi and atomic number 83. It is a post-transition metal and one of the pnictogens, with chemical properties resembling its lighter group 15 siblings arsenic and antimony. Elemental bismuth occurs ...
) sometimes referred to as post-transition metals. Dingle explains the situation this way: :... with 'no-doubt' metals on the far left of the table, and no-doubt non-metals on the far right... the gap between the two extremes is bridged first by the poor ( post-transition) metals, and then by the metalloids—which, perhaps by the same token, might collectively be renamed the 'poor non-metals'. The metalloids tend to be found in forms combined with oxygen or sulfur or (in the case of tellurium) gold or silver. Boron is found in boron-oxygen
borate A borate is any of several boron oxyanions, negative ions consisting of boron and oxygen, such as orthoborate , metaborate , or tetraborate ; or any salt with such anions, such as sodium metaborate, and disodium tetraborate . The name also re ...
minerals including in volcanic spring waters. Silicon occurs in the silicon-oxygen mineral
silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...
(sand). Germanium, arsenic and antimony are mainly found as components of
sulfide Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds la ...
ores. Tellurium occurs in
telluride mineral A telluride mineral is a mineral that has the telluride anion as a main component. Tellurides are similar to sulfides and are grouped with them in both the Dana and Strunz mineral classification systems.http://webmineral.com/strunz/II.shtml Webm ...
s of gold or silver. Native forms of arsenic, antimony and tellurium have been reported.


Allotropes

Most nonmetallic elements exist in allotropic forms. Carbon, for example, occurs as graphite, diamond and other forms. Such allotropes may exhibit physical properties that are more metallic or less nonmetallic. Among the nonmetal halogens, and unclassified nonmetals: * Iodine is known in a semiconducting
amorphous In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid, glassy solid) is a solid that lacks the long-range order that is characteristic of a crystal. Etymology The term comes from the Greek language, Gr ...
form. * Graphite, the standard state of carbon, is a fairly good electrical conductor. The
diamond Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. Another solid form of carbon known as graphite is the chemically stable form of carbon at room temperature and pressure, b ...
allotrope of carbon is clearly nonmetallic, being translucent and an extremely poor electrical conductor. Carbon is known in several other allotropic forms, including semiconducting
buckminsterfullerene Buckminsterfullerene is a type of fullerene with the formula C60. It has a cage-like fused-ring structure (truncated icosahedron) made of twenty hexagons and twelve pentagons, and resembles a soccer ball. Each of its 60 carbon atoms is bonded ...
, and
amorphous In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid, glassy solid) is a solid that lacks the long-range order that is characteristic of a crystal. Etymology The term comes from the Greek language, Gr ...
and paracrystalline (mixed amorphous and crystalline) varieties. * Nitrogen can form gaseous tetranitrogen (N4), an unstable polyatomic molecule with a lifetime of about one microsecond. * Oxygen is a diatomic molecule in its standard state; it also exists as
ozone Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the l ...
(O3), an unstable nonmetallic allotrope with an "indoors"
half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ...
of around half an hour, compared to about three days in ambient air at 20 °C. * Phosphorus, uniquely, exists in several allotropic forms that are more stable than its standard state as white phosphorus (P4). The
white White is the lightest color and is achromatic (having no hue). It is the color of objects such as snow, chalk, and milk, and is the opposite of black. White objects fully reflect and scatter all the visible wavelengths of light. White ...
, red and
black Black is a color which results from the absence or complete absorption of visible light. It is an achromatic color, without hue, like white and grey. It is often used symbolically or figuratively to represent darkness. Black and white ha ...
allotropes are probably the best known; the first is an insulator; the latter two are semiconductors. Phosphorus also exists as
diphosphorus Diphosphorus is an inorganic chemical with the chemical formula . Unlike nitrogen, its lighter pnictogen neighbor which forms a stable N2 molecule with a nitrogen to nitrogen triple bond, phosphorus prefers a tetrahedral form P4 because P-P pi ...
(P2), an unstable diatomic allotrope. * Sulfur has more allotropes than any other element. Amorphous sulfur, a metastable mixture of such allotropes, is noted for its elasticity. * Selenium has several nonmetallic allotropes, all of which are much less electrically conducting than its standard state of gray "metallic" selenium. All the elements most commonly recognized as metalloids form allotropes: * Boron is known in several crystalline and amorphous forms. * Silicon can form crystalline (diamond-like); amorphous; and
orthorhombic In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with ...
Si24 allotropes. * At a pressure of about 10–11 GPa, germanium transforms to a metallic phase with the same tetragonal structure as tin. When decompressed—and depending on the speed of pressure release—metallic germanium forms a series of allotropes that are metastable in ambient conditions. * Arsenic and antimony form several well-known allotropes (yellow, grey, and black). * Tellurium is known in crystalline and amorphous forms. Other allotropic forms of nonmetallic elements are known, either under pressure or in
monolayer A monolayer is a single, closely packed layer of atoms, molecules, or cells. In some cases it is referred to as a self-assembled monolayer. Monolayers of layered crystals like graphene and molybdenum disulfide are generally called 2D materials. C ...
s. Under sufficiently high pressures, at least half of the nonmetallic elements that are semiconductors or insulators, starting with phosphorus at 1.7 GPa, have been observed to form metallic allotropes. Single layer two-dimensional forms of nonmetals include
borophene Borophene is a crystalline atomic monolayer of boron, i.e., it is a two-dimensional allotrope of boron and also known as ''boron sheet''. First predicted by theory in the mid-1990s, different borophene structures were experimentally confirmed i ...
(boron),
graphene Graphene () is an allotrope of carbon consisting of a Single-layer materials, single layer of atoms arranged in a hexagonal lattice nanostructure.
(carbon), silicene (silicon),
phosphorene Phosphorene is a two-dimensional material consisting of phosphorus. It consists of a single layer of the artificially made layered black phosphorus, the most stable allotrope of phosphorus. The designation phosphorene has been introduced in an ...
(phosphorus),
germanene Germanene is a material made up of a single layer of germanium atoms. The material is created in a process similar to that of silicene and graphene, in which high vacuum and high temperature are used to deposit a layer of germanium atoms on a subs ...
(germanium), arsenene (arsenic), antimonene (antimony) and tellurene (tellurium), collectively referred to as '' xenes.''


Prevalence and access


Abundance

Hydrogen and helium are estimated to make up approximately 99% of all ordinary matter in the universe and over 99.9% of its atoms. Oxygen is thought to be the next most abundant element, at about 0.1%. Less than five per cent of the universe is believed to be made of ordinary matter, represented by stars, planets and living beings. The balance is made of
dark energy In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. The first observational evidence for its existence came from measurements of supernovas, which showed that the univ ...
and
dark matter Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not ...
, both of which are currently poorly understood. Five nonmetals namely hydrogen, carbon, nitrogen, oxygen and silicon constitute the bulk of the
Earth's crust Earth's crust is Earth's thin outer shell of rock, referring to less than 1% of Earth's radius and volume. It is the top component of the lithosphere, a division of Earth's layers that includes the crust and the upper part of the mantle. The ...
,
atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A ...
,
hydrosphere The hydrosphere () is the combined mass of water found on, under, and above the surface of a planet, minor planet, or natural satellite. Although Earth's hydrosphere has been around for about 4 billion years, it continues to change in shape. This ...
and
biomass Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bio ...
, in the quantities shown in the table.


Extraction

Nonmetals, and metalloids, are extracted in their raw forms from: Emsley 2011, passim * ''
brine Brine is a high-concentration solution of salt (NaCl) in water (H2O). In diverse contexts, ''brine'' may refer to the salt solutions ranging from about 3.5% (a typical concentration of seawater, on the lower end of that of solutions used for ...
''—chlorine, bromine, iodine; * ''liquid air''—nitrogen, oxygen, neon, argon, krypton, xenon; * ''minerals''—boron ( borate minerals); carbon (coal; diamond; graphite); fluorine (
fluorite Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon. The Mohs sca ...
); silicon (
silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...
); phosphorus (phosphates); antimony ( stibnite,
tetrahedrite Tetrahedrite is a copper antimony sulfosalt mineral with formula: . It is the antimony endmember of the continuous solid solution series with arsenic-bearing tennantite. Pure endmembers of the series are seldom if ever seen in nature. Of the t ...
); iodine (in sodium iodate and
sodium iodide Sodium iodide (chemical formula NaI) is an ionic compound formed from the chemical reaction of sodium metal and iodine. Under standard conditions, it is a white, water-soluble solid comprising a 1:1 mix of sodium cations (Na+) and iodide anions (I ...
); * ''natural gas''—hydrogen, helium, sulfur; and * ''ores'', as processing byproducts—germanium (
zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
ores); arsenic (
copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pink ...
and
lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, ...
ores); selenium, tellurium (copper ores); and radon (
uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
-bearing ores).


Cost

Day to day costs will vary depending on purity, quantity, market conditions, and supplier surcharges. Based on the available literature as at August 2022, while the cited costs of most nonmetals are less than the $US0.80 per gram cost of silver, boron, phosphorus, germanium, xenon, and radon (notionally) are exceptions: *Boron costs around $25 per gram for 99.7% pure polycrystalline chunks with a particle size of about 1 cm. Earlier, in 1997, boron was quoted at $280 per gram for polycrystalline 4 to 6 mm diameter rods of 99.999% purity, about ten times the then $28.35 per gram cost of gold. *In 2020 phosphorus in its most stable black form could "cost up to $1,000 per gram", Boise State University 2020 more than 15 times the cost of gold, whereas ordinary red phosphorus, in 2017, was priced at about $3.40 per kilogram. Researchers hoped to be able to reduce the cost of black phosphorus to as low as $1 per gram. *Germanium and xenon cost about $1.20 and $7.60 per gram. *Up to 2013, radon was available from the
National Institute of Standards and Technology The National Institute of Standards and Technology (NIST) is an agency of the United States Department of Commerce whose mission is to promote American innovation and industrial competitiveness. NIST's activities are organized into physical s ...
for $1,636 per 0.2 ml unit of issue, equivalent to about $86,000,000 per gram, with no indication of a discount for bulk quantities.


Shared uses

Nearly all nonmetals have varying uses in household items; lighting and lasers; and medicine and
pharmaceutical A medication (also called medicament, medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to diagnose, cure, treat, or prevent disease. Drug therapy ( pharmacotherapy) is an important part of the medical field and ...
s. Nitrogen, for example, is found in some garden treatments;
lasers A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fir ...
; and diabetes medicines. Germanium, arsenic, and radon each have uses in one or two of these fields but not all three. Aside from the noble gases most of the remaining nonmetals have, or have had, uses in
agrochemical An agrochemical or agrichemical, a contraction of ''agricultural chemical'', is a chemical product used in industrial agriculture. Agrichemical refers to biocides ( pesticides including insecticides, herbicides, fungicides and nematicides) a ...
s and
dyestuff A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution and ...
s. To the extent that metalloids show metallic character, they have speciality uses extending to (for example) oxide glasses,
alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductili ...
ing components, and semiconductors. Further shared uses of different subsets of the nonmetals occur in or as air replacements;
cryogenics In physics, cryogenics is the production and behaviour of materials at very low temperatures. The 13th IIR International Congress of Refrigeration (held in Washington DC in 1971) endorsed a universal definition of “cryogenics” and “c ...
and
refrigerant A refrigerant is a working fluid used in the refrigeration cycle of air conditioning systems and heat pumps where in most cases they undergo a repeated phase transition from a liquid to a gas and back again. Refrigerants are heavily regulated ...
s;
fertilizer A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
s;
flame retardant The term flame retardants subsumes a diverse group of chemicals that are added to manufactured materials, such as plastics and textiles, and surface finishes and coatings. Flame retardants are activated by the presence of an ignition source and ...
s or
fire extinguishers A fire extinguisher is a handheld active fire protection device usually filled with a dry or wet chemical used to extinguish or control small fires, often in emergencies. It is not intended for use on an out-of-control fire, such as one which ha ...
;
mineral acids A mineral acid (or inorganic acid) is an acid derived from one or more inorganic compounds, as opposed to organic acids which are acidic, organic compounds. All mineral acids form hydrogen ions and the conjugate base when dissolved in water. Char ...
;
plug-in hybrid A plug-in hybrid electric vehicle (PHEV) is a hybrid electric vehicle whose battery pack can be recharged by plugging a charging cable into an external electric power source, in addition to internally by its on-board internal combustion engin ...
vehicles; welding gases; and smart phones.


History, background, and taxonomy


Discovery

Most nonmetals were discovered in the 18th and 19th centuries. Before then carbon, sulfur and antimony were known in
antiquity Antiquity or Antiquities may refer to: Historical objects or periods Artifacts *Antiquities, objects or artifacts surviving from ancient cultures Eras Any period before the European Middle Ages (5th to 15th centuries) but still within the histo ...
; arsenic was discovered during the
Middle Ages In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire ...
(by
Albertus Magnus Albertus Magnus (c. 1200 – 15 November 1280), also known as Saint Albert the Great or Albert of Cologne, was a German Dominican friar, philosopher, scientist, and bishop. Later canonised as a Catholic saint, he was known during his li ...
); and
Hennig Brand Hennig Brand (; c. 1630c. 1692 or c. 1710) was a German alchemist who lived and worked in Hamburg. In 1669, Brand accidentally discovered the chemical element phosphorus while searching for the "philosopher's stone", a substance which was believed ...
isolated phosphorus from urine in 1669. Helium (1868) holds the distinction of being the only element not first discovered on Earth. Radon is the most recently discovered nonmetal, being found only at the end of the 19th century. Chemistry- or physics-based techniques used in the isolation efforts were
spectroscopy Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter ...
,
fractional distillation Fractional distillation is the separation of a mixture into its component parts, or fractions. Chemical compounds are separated by heating them to a temperature at which one or more fractions of the mixture will vaporize. It uses distillation ...
, radiation detection,
electrolysis In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...
, ore acidification,
displacement reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking ...
s,
combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combus ...
and heating; a few nonmetals occurred naturally as free elements Of the noble gases, helium was detected via its yellow line in the coronal spectrum of the sun, and later by observing the bubbles escaping from
uranite Uraninite, formerly pitchblende, is a radioactive, uranium-rich mineral and ore with a chemical composition that is largely UO2 but because of oxidation typically contains variable proportions of U3O8. Radioactive decay of the uranium causes t ...
UO2 dissolved in acid. Neon through xenon were obtained via
fractional distillation Fractional distillation is the separation of a mixture into its component parts, or fractions. Chemical compounds are separated by heating them to a temperature at which one or more fractions of the mixture will vaporize. It uses distillation ...
of air. Radon was first observed emanating from compounds of
thorium Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high ...
, three years after
Henri Becquerel Antoine Henri Becquerel (; 15 December 1852 – 25 August 1908) was a French engineer, physicist, Nobel laureate, and the first person to discover evidence of radioactivity. For work in this field he, along with Marie Skłodowska-Curie and Pie ...
's discovery of radiation in 1896. The nonmetal halogens were obtained from their
halide In chemistry, a halide (rarely halogenide) is a binary chemical compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a flu ...
s via either
electrolysis In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...
, adding an acid, or displacement. Some chemists died as a result of their experiments trying to isolate fluorine. Among the unclassified nonmetals, carbon was known (or produced) as charcoal, soot, graphite and diamond; nitrogen was observed in air from which oxygen had been removed; oxygen was obtained by heating mercurous oxide; phosphorus was liberated by heating ammonium sodium hydrogen phosphate (Na(NH4)HPO4), as found in
urine Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excreted from the body through the urethra. Cellul ...
; sulfur occurred naturally as a free element; and selenium was detected as a residue in
sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...
. Most of the elements commonly recognized as metalloids were isolated by heating their oxides (
boron Boron is a chemical element with the symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the '' boron group'' it has t ...
,
silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ...
,
arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, b ...
,
tellurium Tellurium is a chemical element with the symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionall ...
) or a sulfide (
germanium Germanium is a chemical element with the symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid in the carbon group that is chemically similar to its group neighbors ...
). Antimony was known in its native form as well as being attainable by heating its sulfide.


Origin of the concept

The distinction between
metal A metal (from ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, e ...
s and nonmetals arose, in a convoluted manner, from a crude recognition of different kinds of matter namely pure substances, mixtures, compounds and elements. Thus, matter could be divided into pure substances (such as salt, bicarb of soda, or sulfur) and mixtures ( aqua regia,
gunpowder Gunpowder, also commonly known as black powder to distinguish it from modern smokeless powder, is the earliest known chemical explosive. It consists of a mixture of sulfur, carbon (in the form of charcoal) and potassium nitrate (saltpeter). T ...
, or
bronze Bronze is an alloy consisting primarily of copper, commonly with about 12–12.5% tin and often with the addition of other metals (including aluminium, manganese, nickel, or zinc) and sometimes non-metals, such as phosphorus, or metalloids suc ...
, for example) and pure substances eventually could be distinguished as compounds and elements. "Metallic" elements then seemed to have broadly distinguishable attributes that other elements did not, such as their ability to conduct heat or for their " earths" (
oxide An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...
s) to form
basic BASIC (Beginners' All-purpose Symbolic Instruction Code) is a family of general-purpose, high-level programming languages designed for ease of use. The original version was created by John G. Kemeny and Thomas E. Kurtz at Dartmouth College ...
solutions in water, for example as occurred with
quicklime Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term "'' lime''" connotes calcium-containing inorganic m ...
(CaO).


Use of the term

The term ''nonmetallic'' dates from as far back as 1566. In a medical treatise published that year, Loys de L’Aunay (a French doctor) mentioned the properties of plant substances from metallic and "non-metallic" lands. In early chemistry, Wilhelm Homberg (a German natural philosopher) referred to "non-metallic" sulfur in '' Des Essais de Chimie'' (1708). He questioned the five-fold division of all matter into sulfur, mercury, salt, water and earth, as postulated by (1641) in ''
New Philosophical Light of True Principles and Elements of Nature New is an adjective referring to something recently made, discovered, or created. New or NEW may refer to: Music * New, singer of K-pop group The Boyz Albums and EPs * ''New'' (album), by Paul McCartney, 2013 * ''New'' (EP), by Regurgitator, ...
.'' Homberg's approach represented "an important move toward the modern concept of an element".
Lavoisier Antoine-Laurent de Lavoisier ( , ; ; 26 August 17438 May 1794),
CNRS ( Traité élémentaire de chimie,'' published the first modern list of chemical elements in which he distinguished between gases, metals, nonmetals, and earths (heat resistant oxides). In its first seventeen years, Lavoisier's work was republished in twenty-three editions in six languages, and "carried ... isnew chemistry all over Europe and America."


Suggested distinguishing criteria

In 1809,
Humphry Davy Sir Humphry Davy, 1st Baronet, (17 December 177829 May 1829) was a British chemist and inventor who invented the Davy lamp and a very early form of arc lamp. He is also remembered for isolating, by using electricity, several elements for ...
's discovery of
sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...
and
potassium Potassium is the chemical element with the symbol K (from Neo-Latin '' kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmos ...
"annihilated" the line of demarcation between metals and nonmetals. Before then metals had been distinguished on the basis of their ponderousness or relatively high densities. Sodium and potassium, on the other hand, floated on water and yet were clearly metals on the basis of their chemical behaviour. From as early as 1811, different properties—physical, chemical, and electron related—have been used in attempts to refine the distinction between metals and nonmetals. The accompanying table sets out 22 such properties, by type and date order. Probably the most well-known property is that the electrical conductivity of a metal increases when temperature falls whereas that of a non-metal rises. However this scheme does not work for
plutonium Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exh ...
, carbon, arsenic and antimony. Plutonium, which is a metal, increases its electrical conductivity when heated in the temperature range of around –175 to +125 °C. Carbon, despite being widely regarded as a nonmetal, likewise increases its conductivity when heated. Arsenic and antimony are sometimes classified as nonmetals yet act similarly to carbon. Kneen et al. suggested that the nonmetals could be discerned once a inglecriterion for metallicity had been chosen, adding that, "many arbitrary classifications are possible, most of which, if chosen reasonably, would be similar but not necessarily identical." Emsley noted that, "No single property... can be used to classify all the elements as either metals or nonmetals." Jones added that "classes are usually defined by more than two attributes". Johnson suggested that
physical properties A physical property is any property that is measurable, whose value describes a state of a physical system. The changes in the physical properties of a system can be used to describe its changes between momentary states. Physical properties are ...
can best indicate the metallic or nonmetallic properties of an element, with the proviso that other properties will be needed in ambiguous cases. He observed that all gaseous or nonconducting elements are nonmetals; solid nonmetals metals are hard and brittle or soft and crumbly whereas metals are usually malleable and ductile; and nonmetal oxides are acidic. According to Hein and Arena, nonmetals have low densities and relatively high electronegativity; the accompanying table bears this out. Nonmetallic elements occupy the top left quadrant, where densities are low and electronegativity values are relatively high. The other three quadrants are occupied by metals. Some authors further divide the elements into metals,
metalloids A metalloid is a type of chemical element which has a preponderance of properties in between, or that are a mixture of, those of metals and nonmetals. There is no standard definition of a metalloid and no complete agreement on which elements are ...
, and nonmetals although Odberg argues that anything not a metal is, on categorisation grounds, a nonmetal.


Development of subclasses

A basic taxonomy of nonmetals was set out in 1844, by Alphonse Dupasquier, a French doctor, pharmacist and chemist. To facilitate the study of nonmetals, he wrote: :They will be divided into four groups or sections, as in the following: ::Organogens O, N, H, C ::Sulphuroids S, Se, P ::Chloroides F, Cl, Br, I ::Boroids B, Si. An echo of Dupasquier's fourfold classification is seen in the modern subclasses. The organogens and sulphuroids represent the set of unclassified nonmetals. Varying configurations of these seven nonmetals have been referred to as, for example, basic nonmetals; biogens; central nonmetals; CHNOPS; essential elements; "nonmetals"; orphan nonmetals; or redox nonmetals. The chloroide nonmetals came to be independently referred to as ''halogens.'' The boroid nonmetals expanded into the ''metalloids'', starting from as early as 1864. The noble gases, as a discrete grouping, were counted among the nonmetals from as early as 1900.


Comparison

Some properties of metals, and of metalloids, unclassified nonmetals, nonmetal halogens, and noble gases are summarized in the table.
Physical properties A physical property is any property that is measurable, whose value describes a state of a physical system. The changes in the physical properties of a system can be used to describe its changes between momentary states. Physical properties are ...
apply to elements in their most stable forms in ambient conditions, and are listed in loose order of ease of determination. Chemical properties are listed from general to descriptive, and then to specific. The dashed line around the metalloids denotes that, depending on the author, the elements involved may or may not be recognized as a distinct class or subclass of elements. Metals are included as a reference point. Most properties show a left-to-right progression in metallic to nonmetallic character or average values. The periodic table can thus be indicatively divided into metals and nonmetals, with more or less distinct gradations seen among the nonmetals. Vernon 2020, pp. 217–225


See also

*
CHON CHON is a mnemonic acronym for the four most common elements in living organisms: carbon, hydrogen, oxygen, and nitrogen. The acronym CHNOPS, which stands for ''c''arbon, ''h''ydrogen, ''n''itrogen, ''o''xygen, ''p''hosphorus, ''s''ulfur, ...
(carbon, hydrogen, oxygen, nitrogen) * List of nonmetal monographs *
Metallization pressure Metallization pressure is the pressure required for a non-metallic chemical element to become a metal. Every material is predicted to turn into a metal if the pressure is high enough, and temperature low enough. The value for arsenic refers to pre ...
*
Period 1 A period 1 element is one of the chemical elements in the first row (or period) of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate periodic (recurring) trends in the chemical behaviour of th ...
elements (hydrogen, helium) * Properties of nonmetals (and metalloids) by group


Notes


References


Citations


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John Scoffern John Scoffern (1814–1882) was an English surgeon and popular science writer. Life He was born in Dutson, Cornwall, the son of William Scoffern (1783–1854) and his wife Wilmot Crocker, was educated by the Rev. John Couch Grylls at Saltash. He ...
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External links

* {{Authority control Periodic table