Non-metals

In chemistry, a nonmetal is a chemical element that generally lacks a predominance of metallic properties; they range from colorless gases (like hydrogen) to shiny solids (like carbon, as graphite). The electrons 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 electrons in chemical reactions and to form acidic compounds.

Two nonmetals, hydrogen and helium, make up about 99% of ordinary matter in the observable universe by mass. Five nonmetallic elements, hydrogen, carbon, nitrogen, oxygen and silicon, largely make up the Earth's crust, atmosphere, 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 pharmaceuticals; lighting and lasers; 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 extract.

Definition and applicable elements

A nonmetal is a chemical element 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, oxygen, nitrogen, and sulfur; the highly reactive halogens fluorine, chlorine, bromine, and iodine; and the noble gases helium, neon, argon, krypton, xenon, and radon (see e.g. Larrañaga et al). The authors recognized carbon, phosphorus and selenium as nonmetals; Vernon had earlier reported that these three elements were instead sometimes counted as metalloids. The elements commonly recognized as metalloids namely boron; silicon and germanium; arsenic and antimony; and tellurium 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, 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 (''Z'' = 112), flerovium (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, 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 points and boiling points, and are poor conductors of heat and electricity. 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 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 bonds, 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 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 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 configurations 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 and octet rules of thumb (and for metals there is a less rigorously predictive 18-electron rule).

Nonmetals mostly have higher ionization energies, electron affinities, electronegativity values, and standard reduction potentials 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 protons in the atomic nucleus 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 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 (), used in ceramic glazes; selenocysteine (), the 21st amino acid of life; phosphorus sesquisulfide (P₄S₃), in strike anywhere matches; and teflon ()''_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. 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 snowflakes their hexagonal symmetry, binds DNA into a double helix; shapes the three-dimensional forms of proteins; 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. The small atomic radii of carbon, nitrogen, and oxygen facilitate the formation of double 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 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 and lutetium, ultimately resulting in smaller than expected atomic radii for the elements from hafnium (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 states other than the lowest for their group (that is, 3, 2, 1, or 0) for example in phosphorus pentachloride (PCl₅), sulfur hexafluoride (SF₆), iodine heptafluoride (IF₇), and xenon difluoride (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 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 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 heavy metals.
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 cationic behavior, which is unusual for a nonmetal.

Noble gases

Six nonmetals are classified as noble gases: helium, neon, argon, krypton, xenon, 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.

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 masses 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 gases and noble metals 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, 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 to the extent of as much as 7%. Radon diffuses out of rocks, where it is formed during the natural decay sequence of uranium and thorium. 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 (NaF); ordinary table salt (NaCl); swimming pool disinfectant ( NaBr); or food supplements ( KI). The word "halogen" means "salt 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 (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 agents. Manifestations of this status include their corrosive nature. Daniel & Rapp 1976, p. 55 All four exhibit a tendency to form predominately ionic compounds 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 (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, attributing these inclusions as a result of radiation from the presence of tiny amounts of uranium.

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 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 hydrides, featuring metallic bonding, with some transition metals. 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 and geochemical 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 cells. Acid rain is caused by dissolved nitrogen or sulfur. Oxygen corrodes iron via rust. White phosphorus, the most unstable form, ignites in air and produces phosphoric acid residue. Untreated selenium in soils can give rise to corrosive hydrogen selenide gas. When combined with metals, the unclassified nonmetals can form high hardness (interstitial or refractory) 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 as a component of methane and hydrogen sulfide.
* Carbon occurs in limestone, dolomite, and marble, as carbonates. Less well known is carbon as graphite, which mainly occurs in metamorphic 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 minerals.
* Phosphorus minerals are widespread, usually as phosphorus-oxygen phosphates.
* 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 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.

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 and bismuth) 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 minerals including in volcanic spring waters. Silicon occurs in the silicon-oxygen mineral silica (sand). Germanium, arsenic and antimony are mainly found as components of sulfide ores. Tellurium occurs in telluride minerals 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 form.
* Graphite, the standard state of carbon, is a fairly good electrical conductor. The diamond 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, and amorphous 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 (O₃), an unstable nonmetallic allotrope with an "indoors" half-life 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, red and black allotropes are probably the best known; the first is an insulator; the latter two are semiconductors. Phosphorus also exists as diphosphorus (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 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 monolayers. 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 (boron), graphene (carbon), silicene (silicon), phosphorene (phosphorus), germanene (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 and dark matter, both of which are currently poorly understood.

Five nonmetals namely hydrogen, carbon, nitrogen, oxygen and silicon constitute the bulk of the Earth's crust, atmosphere, hydrosphere and biomass, in the quantities shown in the table.

Extraction

Nonmetals, and metalloids, are extracted in their raw forms from: Emsley 2011, passim
* ''brine''—chlorine, bromine, iodine;
* ''liquid air''—nitrogen, oxygen, neon, argon, krypton, xenon;
* ''minerals''—boron (borate minerals); carbon (coal; diamond; graphite); fluorine (fluorite); silicon (silica); phosphorus (phosphates); antimony (stibnite, tetrahedrite); iodine (in sodium iodate and sodium iodide);
* ''natural gas''—hydrogen, helium, sulfur; and
* ''ores'', as processing byproducts—germanium (zinc ores); arsenic (copper and lead ores); selenium, tellurium (copper ores); and radon (uranium-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 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 pharmaceuticals. Nitrogen, for example, is found in some garden treatments; lasers; 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 agrochemicals and dyestuffs. To the extent that metalloids show metallic character, they have speciality uses extending to (for example) oxide glasses, alloying components, and semiconductors.

Further shared uses of different subsets of the nonmetals occur in or as air replacements; cryogenics and refrigerants; fertilizers; flame retardants or fire extinguishers; mineral acids; plug-in hybrid 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; arsenic was discovered during the Middle Ages (by Albertus Magnus); and Hennig Brand 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, fractional distillation, radiation detection, electrolysis, ore acidification, displacement reactions, combustion 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 UO₂ dissolved in acid. Neon through xenon were obtained via fractional distillation of air. Radon was first observed emanating from compounds of thorium, three years after Henri Becquerel's discovery of radiation in 1896.

The nonmetal halogens were obtained from their halides via either electrolysis, 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; sulfur occurred naturally as a free element; and selenium was detected as a residue in sulfuric acid.

Most of the elements commonly recognized as metalloids were isolated by heating their oxides (boron, silicon, arsenic, tellurium) or a sulfide (germanium). Antimony was known in its native form as well as being attainable by heating its sulfide.

Origin of the concept

The distinction between metals 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, or bronze, 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" (oxides) to form basic solutions in water, for example as occurred with quicklime (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.'' Homberg's approach represented "an important move toward the modern concept of an element".

Lavoisier, in his "revolutionary" 1789 work '' 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's discovery of sodium and potassium "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, 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 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, 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 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 (carbon, hydrogen, oxygen, nitrogen)
* List of nonmetal monographs
* Metallization pressure
* Period 1 elements (hydrogen, helium)
* Properties of nonmetals (and metalloids) by group

Notes

References

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