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.

A periodic table showing 14 elements listed by nearly all authors as nonmetals (the noble gases plus fluorine, chlorine, bromine, iodine, nitrogen, oxygen, and sulfur); 3 elements listed by most authors as nonmetals (carbon, phosphorus and selenium); and 6 elements listed as nonmetals by some authors (boron, silicon, germanium, arsenic, antimony). Nearby metals are aluminium, gallium, indium, thallium, tin, lead, bismuth, polonium, and astatine.

Extract of periodic table showing how often each element is classified as a nonmetal:
 14  effectively always[n 1]  3  frequently[n 2]  6  sometimes (metalloids)[n 3]
Nearby metals are shown in a gray font.[n 4]
There is no precise definition of a nonmetal; which elements are counted as such varies.
Hydrogen is usually in group 1 (per the below full table) but can be in group 17 (per the above extract).[n 5]
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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 elementsEdit

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.[8] Since there is no rigorous definition of a nonmetal,[9][10][11] 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.[12]

Although Steudel,[13] in 2020, recognised twenty-three elements as nonmetals, any such list is open to challenge.[1] 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).[1] The authors recognized carbon, phosphorus and selenium as nonmetals; Vernon[2] 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.[14] At other times they are counted as nonmetals in light of their nonmetallic chemistry.[4]

Of the 118 known elements[15] no more than about 20% are regarded as nonmetals.[16] The status of a few elements is less certain. Astatine, the fifth halogen, is often ignored on account of its rarity and intense radioactivity;[17] theory and experimental evidence suggest it is a metal.[18] The superheavy elements copernicium (Z = 112), flerovium (114), and oganesson (118) may turn out to be nonmetals; their status has not been confirmed.[19]

General propertiesEdit


Physical properties apply to elements in their most stable forms in ambient conditions
Variety in color and form
of some nonmetallic elements
Boron in its β-rhombohedral phase
Metallic appearance of carbon as graphite
Blue color of liquid oxygen
Pale yellow liquid fluorine in a cryogenic bath
Sulfur as a yellow powder
Liquid bromine at room temperature
Metallic appearance of iodine under white light
Liquefied xenon

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.[20] The solid elements have low densities, are brittle or crumbly with low mechanical and structural strength,[21] and poor to good conductors.[n 6]

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.[25] Many are gases at room temperature. Nonmetals that form giant structures, such as chains of up to 1,000 atoms (e.g. selenium),[26] 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,[27] carbon,[28] phosphorus,[29] arsenic,[30] selenium,[31] antimony,[32] tellurium,[33] and iodine.[34]

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.[35] The colored nonmetals (sulfur, fluorine, chlorine, bromine) absorb some colours (wavelengths) and transmit the complementary colours. For chlorine, its "familiar yellow-green due to a broad region of absorption in the violet and blue regions of the spectrum".[36][n 7] 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.[38]

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[39] the electrons in nonmetals typically lack such mobility.[40] Among the nonmetallic elements, good electrical and thermal conductivity occurs only in carbon, arsenic and antimony.[n 8] Good thermal conductivity otherwise occurs only in boron, silicon, phosphorus, and germanium;[22] such conductivity is transmitted though vibrations of the crystalline lattices of these elements.[41] Moderate electrical conductivity occurs in boron, silicon, phosphorus, germanium, selenium, tellurium and iodine.[n 9] Plasticity occurs in limited circumstances only in carbon, phosphorus, sulfur, and selenium.[n 10]

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.[48]


Some chemistry-based typical
differences between metals and nonmetals[49]
Aspect Metals Nonmetals
Electronegativity Lower than nonmetals,
with some exceptions[50]
Moderate to very high
Seldom form
covalent bonds
Frequently form
covalent bonds
Metallic bonds (alloys)
between metals
Covalent bonds
between nonmetals
Ionic bonds between nonmetals and metals
Positive Negative or positive
Oxides Basic in lower oxides;
increasingly acidic
in higher oxides
never basic[51]
In aqueous
Exist as cations Exist as anions
or oxyanions

Nonmetals have moderate to high values of electronegativity[53] 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.[n 11]

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).[56]

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.[57]

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.[58] There is an associated reduction in atomic radius[59] as the increasing nuclear charge draws the outer electrons closer to the core.[60] 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.[61]

The number of compounds formed by nonmetals is vast.[62] 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.[63] A few examples of nonmetal compounds are: boric acid (H
), used in ceramic glazes; selenocysteine (C
), the 21st amino acid of life;[64] phosphorus sesquisulfide (P4S3), in strike anywhere matches; and teflon ((C
)n),[65] as used in non-stick coatings for pans and other cookware.


Periodic table highlighting the first row of each block.[n 12] Helium (He), as a noble gas, is normally shown over neon (Ne) with the rest of the noble gases. The elements within scope of this article are inside the thick black borders. The status of oganesson (Og, element 118) is not yet known.
Electronegativity values of the group 16 chalcogen elements showing a W-shaped alternation or secondary periodicity going down the group

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,[66] and unusual oxidation states in the heavier nonmetals.

First row anomalyEdit

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.[67] 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.[68] 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."[69]

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.[70] 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.[71]

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.[72]

Secondary periodicityEdit

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.[73] 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.[74]

Unusual oxidation statesEdit

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).[75]

Subclasses Edit

Modern periodic table extract showing nonmetal subclasses. H is usually shown in group 1 but can instead be in group 17.[n 13]
† moderately strong oxidising agent ‡ strong oxidising agent[n 14]

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".[87] 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.[88]

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[89] (the term used here) or stable halogens;[90]
  • 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[91] sometimes considered to be nonmetals and sometimes not.[n 15]

Since the metalloids occupy "frontier territory",[93] 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[94] or as a sub-class of nonmetals.[95] Other authors count some of them as metals, for example arsenic and antimony, due to their similarities to heavy metals.[96][n 16] 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)[97] 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.[98]

Noble gasesEdit

A small (about 2 cm long) piece of rapidly melting argon ice

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.[99]

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.[100] That is why they are all gases under standard conditions, even those with atomic masses larger than many normally solid elements.[101]

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,[102] with most of these involving oxygen or fluorine combining with either krypton, xenon or radon.[103]

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.[104] 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.[105]

About 1015 tonnes of noble gases are present in the Earth's atmosphere.[106] Helium is additionally found in natural gas to the extent of as much as 7%.[107] Radon diffuses out of rocks, where it is formed during the natural decay sequence of uranium and thorium.[108] 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."[109]

Nonmetal halogensEdit

A cluster of purple fluorite CaF
, a fluorine mineral, between two quartzes

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".[110]

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[76] solid. Electrically, the first three are insulators while iodine is a semiconductor (along its planes).[111]

Chemically, they have high ionization energies, electron affinities, and electronegativity values, and are mostly relatively strong oxidizing agents.[112] Manifestations of this status include their corrosive nature.[113] All four exhibit a tendency to form predominately ionic compounds with metals[114] whereas the remaining nonmetals, bar oxygen, tend to form predominately covalent compounds with metals.[n 17] The reactive and strongly electronegative nature of the nonmetal halogens represents the epitome of nonmetallic character.[118]

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.[119] 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).[120]

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 (F
) by weight in antozonite, attributing these inclusions as a result of radiation from the presence of tiny amounts of uranium.[121]

Unclassified nonmetalsEdit

Selenium conducts electricity around 1,000 times better when light falls on it, a property used in light-sensing applications.[122]

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[123] and a semiconductor in a direction perpendicular to its planes;[124] phosphorus and selenium are semiconductors;[125] and hydrogen, nitrogen, oxygen, and sulfur are insulators.[n 18]

They are generally regarded as being too diverse to merit a collective examination,[127] and have been referred to as other nonmetals,[128] or more plainly as nonmetals, located between the metalloids and the halogens.[129] Consequently, their chemistry tends to be taught disparately, according to their four respective periodic table groups,[130] 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.[n 19]

Hydrogen, in particular, behaves in some respects like a metal and in others like a nonmetal.[132] Like a metal it can (first) lose its single electron;[133] it can stand in for alkali metals in typical alkali metal structures;[134] and is capable of forming alloy-like hydrides, featuring metallic bonding, with some transition metals.[135] 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.[136] It does this by way of forming a covalent or ionic bond[135] or, if it has lost its electron, attaching itself to a lone pair of electrons.[137]

Some or all of these nonmetals nevertheless have several shared properties. Most of them, being less reactive than the halogens,[138] can occur naturally in the environment.[139] They have prominent biological[140][141] and geochemical roles.[127] While their physical and chemical character is "moderately non-metallic", on a net basis,[127] all of them have corrosive aspects. Hydrogen can corrode metals. Carbon corrosion can occur in fuel cells.[142] 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.[143] Untreated selenium in soils can give rise to corrosive hydrogen selenide gas.[144] When combined with metals, the unclassified nonmetals can form high hardness (interstitial or refractory) compounds,[145] on account of their relatively small atomic radii and sufficiently low ionization energy values.[127] They show a tendency to bond to themselves, especially in solid compounds.[146][127] Diagonal periodic table relationships among these nonmetals echo similar relationships among the metalloids.[147][148]

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 ... [and] ... form a transitional bridge between the two".[149]

Unclassified nonmetals typically occur in elemental forms (oxygen, sulfur) or are found in association with either of these two elements:[150]

  • Hydrogen occurs in the world's oceans as a component of water, and in natural gas as a component of methane and hydrogen sulfide.[151]
  • Carbon occurs in limestone, dolomite, and marble, as carbonates.[152] Less well known is carbon as graphite, which mainly occurs in metamorphic silicate rocks[153] as a result of the compression and heating of sedimentary carbon compounds.[154]
  • 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.[155]
  • 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.[156]
  • Selenium occurs in metal sulfide ores, where it partially replaces the sulfur; elemental selenium is occasionally found.[157]


A crystal of realgar, also known as "ruby sulphur" or "ruby of arsenic", an arsenic sulfide mineral As4S4

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.[2]

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.[2]

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.[2]

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)[158] sometimes referred to as post-transition metals.[159] 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'.[160]

The metalloids tend to be found in forms combined with oxygen or sulfur or (in the case of tellurium) gold or silver.[150] 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.[161]


Brownish crystals of buckminsterfullerene (С60), a semiconducting allotrope of carbon

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.[162]

Among the nonmetal halogens, and unclassified nonmetals:

  • Iodine is known in a semiconducting amorphous form.[163]
  • 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.[164] Carbon is known in several other allotropic forms, including semiconducting buckminsterfullerene,[165] and amorphous[166] and paracrystalline (mixed amorphous and crystalline)[167] varieties.
  • Nitrogen can form gaseous tetranitrogen (N4), an unstable polyatomic molecule with a lifetime of about one microsecond.[168]
  • 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.[169]
  • 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.[170] Phosphorus also exists as diphosphorus (P2), an unstable diatomic allotrope.[171]
  • Sulfur has more allotropes than any other element.[172] Amorphous sulfur, a metastable mixture of such allotropes, is noted for its elasticity.[173]
  • Selenium has several nonmetallic allotropes, all of which are much less electrically conducting than its standard state of gray "metallic" selenium.[174]

All the elements most commonly recognized as metalloids form allotropes:

  • Boron is known in several crystalline and amorphous forms.[175]
  • Silicon can form crystalline (diamond-like); amorphous; and orthorhombic Si24 allotropes.[176]
  • 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.[177]
  • Arsenic and antimony form several well-known allotropes (yellow, grey, and black).[178]
  • Tellurium is known in crystalline and amorphous forms.[179]

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,[n 20] starting with phosphorus at 1.7 GPa, have been observed to form metallic allotropes.[181][n 21] 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.[183]

Prevalence and accessEdit


Approximate nonmetal composition
of the Earth and its biomass, by weight[184]
Domain Main components Next most
Crust O 61%, Si 20% H 2.9%
Atmosphere N 78%, O 21% Ar 0.5%
Hydrosphere O 66.2%, H 33.2% Cl 0.3%
Biomass O 63%, C 20%, H 10% N 3.0%

Hydrogen and helium are estimated to make up approximately 99% of all ordinary matter in the universe and over 99.9% of its atoms.[185] Oxygen is thought to be the next most abundant element, at about 0.1%.[186] 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.[187]

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.


Germanium occurs in some zinc-copper-lead ore bodies, in quantities sufficient to justify extraction.[188] In 2021, the 99.999% pure form was priced at US$1200 per kilogram.[189]

Nonmetals, and metalloids, are extracted in their raw forms from:[139]

  • 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).


Day to day costs will vary depending on purity, quantity, market conditions, and supplier surcharges.[190]

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,[191] 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.[192] Earlier, in 1997, boron was quoted at $280 per gram for polycrystalline 4 to 6 mm diameter rods of 99.999% purity,[193] about ten times the then $28.35 per gram cost of gold.[194]
  • In 2020 phosphorus in its most stable black form could "cost up to $1,000 per gram",[195] more than 15 times the cost of gold, whereas ordinary red phosphorus, in 2017, was priced at about $3.40 per kilogram.[196] Researchers hoped to be able to reduce the cost of black phosphorus to as low as $1 per gram.[195]
  • Germanium and xenon cost about $1.20 and $7.60 per gram.[197]
  • 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.[198]

Shared usesEdit

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.[139] Aside from the noble gases most of the remaining nonmetals have, or have had, uses in agrochemicals and dyestuffs.[139] To the extent that metalloids show metallic character, they have speciality uses extending to (for example) oxide glasses, alloying components, and semiconductors.[199]

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.[139]

History, background, and taxonomyEdit


The Alchemist Discovering Phosphorus (1771) by Joseph Wright. The alchemist is Hennig Brand; the glow emanates from the combustion of phosphorus inside the flask.

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.[n 22] Radon is the most recently discovered nonmetal, being found only at the end of the 19th century.[139]

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.[201]

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.[202]

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;[203] sulfur occurred naturally as a free element; and selenium[n 23] was detected as a residue in sulfuric acid.[205]

Most of the elements commonly recognized as metalloids were isolated by heating their oxides (boron, silicon, arsenic, tellurium) or a sulfide (germanium).[139] Antimony was known in its native form as well as being attainable by heating its sulfide.[206]

Origin of the conceptEdit

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.[207] "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).[208]

Use of the termEdit

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.[209]

In early chemistry, Wilhelm Homberg (a German natural philosopher) referred to "non-metallic" sulfur in Des Essais de Chimie (1708).[210] He questioned the five-fold division of all matter into sulfur, mercury, salt, water and earth, as postulated by Étienne de Clave [fr] (1641) in New Philosophical Light of True Principles and Elements of Nature.[211] Homberg's approach represented "an important move toward the modern concept of an element".[212]

Lavoisier, in his "revolutionary"[213] 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).[214] In its first seventeen years, Lavoisier's work was republished in twenty-three editions in six languages, and "carried ... [his] new chemistry all over Europe and America."[215]

Suggested distinguishing criteriaEdit

Some single properties used to distinguish between
metals and nonmetals listed by type and date of source

Electron related

In 1809, Humphry Davy's discovery of sodium and potassium "annihilated"[236] the line of demarcation between metals and nonmetals. Before then metals had been distinguished on the basis of their ponderousness or relatively high densities.[237] Sodium and potassium, on the other hand, floated on water and yet were clearly metals on the basis of their chemical behaviour.[238]

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.[228] 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.[239] Carbon, despite being widely regarded as a nonmetal, likewise increases its conductivity when heated.[240] Arsenic and antimony are sometimes classified as nonmetals yet act similarly to carbon.[241]

Kneen et al. suggested that the nonmetals could be discerned once a [single] criterion 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."[12] Emsley noted that, "No single property ... can be used to classify all the elements as either metals or nonmetals."[242] Jones added that "classes are usually defined by more than two attributes".[243]

The first 99 elements sorted by
density and electronegativity (EN)[n 25]
Density < 1.9 ≥ 1.9
< 7 gm/cm3 Groups 1 and 2
Sc, Y, La
Ce, Pr, Eu, Yb
Ti, Zr, V; Al, Ga
Noble gases
F, Cl, Br, I
H, C, N, P, O, S, Se
B, Si, Ge, As, Sb, Te
> 7 gm/cm3 Nd, Pm, Sm, Gd, Tb, Dy
Ho, Er, Tm, Lu; Ac–Es;
Hf, Nb, Ta; Cr, Mn, Fe,
Co, Zn, Cd, In, Tl, Pb
Ni, Mo, W, Tc, Re,
Platinum group metals,
Coinage metals, Hg; Sn,
Bi, Po, At

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.[249]

According to Hein and Arena, nonmetals have low densities and relatively high electronegativity;[250] 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.[251]

Development of subclassesEdit

A basic taxonomy of nonmetals was set out in 1844, by Alphonse Dupasquier, a French doctor, pharmacist and chemist.[252] To facilitate the study of nonmetals, he wrote:[253]

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;[254] biogens;[255] central nonmetals;[256] CHNOPS;[257] essential elements;[258] "nonmetals";[259][n 26] orphan nonmetals;[260] or redox nonmetals.[261] The chloroide nonmetals came to be independently referred to as halogens.[262] The boroid nonmetals expanded into the metalloids, starting from as early as 1864.[263] The noble gases, as a discrete grouping, were counted among the nonmetals from as early as 1900.[264]


Some properties of metals, and of metalloids, unclassified nonmetals, nonmetal halogens, and noble gases are summarized in the table.[n 27] 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.[265]

Some cross-subclass properties
Physical property Metals
alkali, alkaline earth, lanthanide, actinide, transition, post-transition
boron, silicon, germanium, arsenic, antimony, tellurium
Unclassified nonmetals
hydrogen, carbon, nitrogen, phosphorus, oxygen, sulfur, selenium
Nonmetal halogens
fluorine, chlorine, bromine, iodine
Noble gases
helium, neon, argon, krypton, xenon, radon
Form and heft[266]
  • ◇ solid
  • ◇ low to higher density
  • ◇ all lighter than Fe
  • ◇ solid or gas
  • ◇ low density
  • ◇ H, N lighter than air[267]
  • ◇ solid, liquid or gas
  • ◇ low density
  • ◇ gas
  • ◇ low density
  • ◇ He, Ne lighter than air[268]
Appearance lustrous[20] lustrous[269]
  • ◇ lustrous: C, P, Se[270]
  • ◇ colorless: H, N, O[271]
  • ◇ colored: S[272]
  • ◇ colored: F, Cl, Br[273]
  • ◇ lustrous: I[2]
Elasticity mostly malleable and ductile[20] (Hg is liquid) brittle[269] C, black P, S, Se brittle; all four have less stable non-brittle forms[275][n 28] iodine is brittle[277] not applicable
Electrical conductivity good[n 29]
  • ◇ moderate: B, Si, Ge, Te
  • ◇ good: As, Sb[n 30]
  • ◇ poor: H, N, O, S
  • ◇ moderate: P, Se
  • ◇ good: C[n 31]
  • ◇ poor: F, Cl, Br
  • ◇ moderate: I[n 32]
poor[n 33]
Electronic structure[180] metallic (Bi is a semimetal) semimetal (As, Sb) or semiconductor
  • ◇ semimetal: C
  • ◇ semiconductor: P, Se
  • ◇ insulator: H, N, O, S
semiconductor (I) or insulator insulator
Chemical property Metals
alkali, alkaline earth, lanthanide, actinide, transition, post-transition
boron, silicon, germanium, arsenic, antimony, tellurium
Unclassified nonmetals
hydrogen, carbon, nitrogen, phosphorus, oxygen, sulfur, selenium
Nonmetal halogens
fluorine, chlorine, bromine, iodine
Noble gases
helium, neon, argon, krypton, xenon, radon
General chemical behavior
weakly nonmetallic[n 34] moderately nonmetallic[283] strongly nonmetallic[284]
  • ◇ inert to nonmetallic[285]
  • ◇ Rn shows some cationic behavior[286]
  • ◇ basic; some amphoteric or acidic[287]
  • ◇ V; Mo, W; Al, In, Tl; Sn, Pb; Bi are glass formers[288]
  • ◇ ionic, polymeric, layer, chain, and molecular structures[289]
  • ◇ acidic (NO
    , N
    , SO
    , SeO
    strongly so)[294][295] or neutral (H2O, CO, NO, N2O)[n 36]
  • ◇ P, S, Se are glass formers;[288] CO2 forms a glass at 40 GPa[297]
  • ◇ mostly molecular[293]
  • ◇ C, P, S, Se have at least one polymeric form
  • ◇ acidic; ClO
    , Cl
    , I
    strongly so[295][294]
  • ◇ no glass formers reported
  • ◇ molecular[293]
  • ◇ iodine has at least one polymeric form, I2O5[298]
  • ◇ metastable XeO3 is acidic;[299] stable XeO4 strongly so[300]
  • ◇ no glass formers reported
  • ◇ molecular[293]
  • XeO2 is polymeric[301]
Compounds with metals alloys[20] or intermetallic compounds[302] tend to form alloys or intermetallic compounds[303]
  • ◇ salt-like to covalent: H†, C, N, P, S, Se[4]
  • ◇ mainly ionic: O[304]
mainly ionic[114] simple compounds in ambient conditions not known[n 37]
Ionization energy (kJ mol−1)‡
(data page)
  • ◇ low to high
  • ◇ 376 to 1,007
  • ◇ average 643
  • ◇ moderate
  • ◇ 762 to 947
  • ◇ average 833
  • ◇ moderate to high
  • ◇ 941 to 1,402
  • ◇ average 1,152
  • ◇ high
  • ◇ 1,008 to 1,681
  • ◇ average 1,270
  • ◇ high to very high
  • ◇ 1,037 to 2,372
  • ◇ average 1,589
Electronegativity (Pauling)[n 38]
(data page)
  • ◇ low to high
  • ◇ 0.79 to 2.54
  • ◇ average 1.5
  • ◇ moderate
  • ◇ 1.9 to 2.18
  • ◇ average 2.05
  • ◇ moderate to high
  • ◇ 2.19 to 3.44
  • ◇ average 2.65
  • ◇ high
  • ◇ 2.66 to 3.98
  • ◇ average 3.19
  • ◇ high (Rn) to very high
  • ◇ ca. 2.43 to 4.7
  • ◇ average 3.3
† Hydrogen can also form alloy-like hydrides[307]
‡ The labels low, moderate, high, and very high are arbitrarily based on the value spans listed in the table

See alsoEdit


  1. ^ H; N; O, S; F, Cl, Br, I; He, Ne, Ar, Kr, Xe, Rn[1]
  2. ^ C; P; Se.[1] On the other hand, these three elements were counted as metalloids in a survey of 194 lists of metalloids, 16, 10, and 46 times respectively.[2]
  3. ^ B; Si, Ge; As, Sb; Te[3][4]
  4. ^ Al, Ga, In, Tl; Sn, Pb; Bi; Po; At
  5. ^ Hydrogen has historically been placed over one or more of lithium, boron,[5] carbon, or fluorine;[6] or over no group at all; or over all main groups simultaneously, and therefore may or may not be adjacent to other nonmetals.[7]
  6. ^ The solid nonmetals have thermal conductivity values of from 0.27 W m–1 K–1 for sulfur to 2,000 for carbon cf. 6.3 for neptunium to 429 for silver, metals both;[22] electrical conductivity values range from 10−18 S•cm−1 for sulfur[22] to 3 × 104 in graphite[23] or 3.9 × 104 for arsenic[24] cf. 0.69 × 104 for manganese to 63 × 104 for silver, metals both.[22]
  7. ^ The absorbed light may be converted to heat or re-emitted in all directions so that the emission spectrum is thousands of times weaker than the incident light radiation.[37]
  8. ^ Thermal conductivity values for metals range from 6.3 W m–1 K–1 for neptunium to 429 for silver; cf. antimony 24.3, arsenic 50, and carbon 2000;[22] electrical conductivity values of metals range from 0.69 S•cm−1 × 104 for manganese to 63 × 104 for silver; cf. carbon 3 × 104,[23] arsenic 3.9 × 104 and antimony 2.3 × 104[22]
  9. ^ These elements being semiconductors[42]
  10. ^ For example, C as exfoliated (expanded) graphite[43] and as carbon nanotube wire;[44] P as white phosphorus (soft as wax, pliable and can be cut with a knife, at room temperature);[45] S as plastic sulfur;[46] and Se as selenium wires, drawn from the molten form[47]
  11. ^ Acids are formed by boron, phosphorus, selenium, arsenic, iodine;[54] oxides by carbon, silicon, germanium, sulfur, antimony, and tellurium.[55]
  12. ^ These elements are hydrogen and helium in the s-block; boron to neon in the p-block; scandium to zinc in the d-block; and lanthanum to ytterbium in the f-block.
  13. ^ Noble gases: He, Ne, Ar, Kr, Xe, Rn; Nonmetal halogens: F, Cl, Br, I; Unclassified nonmetals: H, C, N, P, O, S, Se; Metalloids: B, Si, Ge, As, Sb, Te. Nearby metals are Al, Ga, In, Tl; Sn, Pb; Bi; Po; and At.
  14. ^ The seven nonmetals marked with single or double daggers each have a lackluster appearance and discrete molecular structures, but for I which has a metallic appearance under white light.[76] The remaining reactive nonmetallic elements have giant covalent structures, but for H which is a diatomic gas.[77]

    The single dagger nonmetals N, S and iodine are somewhat hobbled as "strong" nonmetals.

    While N has a high electronegativity, it is a reluctant anion former,[78] and a pedestrian oxidizing agent unless combined with a more active non-metal like O or F.[79]

    S reacts in the cold with alkalic and post-transition metals, and Cu, Ag and Hg,[80] but otherwise has low values of ionization energy, electron affinity, and electronegativity compared to the averages of the others; it is regarded as being not a particularly good oxidizing agent.[81]
    Iodine is sufficiently corrosive to cause lesions resembling thermal burns, if handled without suitable protection,[82] and tincture of iodine will smoothly dissolve Au.[83] That said, while "F, Cl and Br will all oxidize Fe2+ (aq) to Fe3+(aq) ... iodine ... is such a [relatively] weak oxidizing agent that it cannot remove electrons from Fe(II) ions to form Fe(III) ions."[84] Thus, for the reaction X2 + 2e → 2X(aq) the reduction potentials are F +2.87 V; Cl +1.36; Br +1.09; I +0.54. Here Fe3+ + e → Fe3+ +0.77.[85] Thus F2, Cl2 and Br2 will oxidize Fe2+ to Fe3+ but Fe3+ will oxidize I to I2. Iodine has previously been referred to as a moderately strong oxidizing agent.[86]
  15. ^ Tshitoyan et al. (2019) conducted a machine-based analysis of the proximity of names of the elements based on 3.3 million abstracts published between 1922 and 2018 in more than 1,000 journals. The resulting map shows that "chemically similar elements are seen to cluster together and the overall distribution exhibits a topology reminiscent of the periodic table itself".[92]
  16. ^ Jones takes a philosophical or pragmatic view to these questions. He writes: "Though classification is an essential feature of all branches of science, there are always hard cases at the boundaries. The boundary of a class is rarely sharp ... Scientists should not lose sleep over the hard cases. As long as a classification system is beneficial to economy of description, to structuring knowledge and to our understanding, and hard cases constitute a small minority, then keep it. If the system becomes less than useful, then scrap it and replace it with a system based on different shared characteristics".[97]
  17. ^ Metal oxides are usually ionic.[115] On the other hand, oxides of metals with high oxidation states are usually either polymeric or covalent.[116] A polymeric oxide has a linked structure composed of multiple repeating units.[117]
  18. ^ Sulfur, an insulator, and selenium, a semiconductor are each photoconductors—their electrical conductivities increase by up to six orders of magnitude when exposed to light.[126]
  19. ^ For example, Wulfsberg divides the nonmetals, including B, Si, Ge, As, Sb, Te, Xe, into very electronegative nonmetals (Pauling electronegativity over 2.8) and electronegative nonmetals (1.9 to 2.8). This results in N and O being very electronegative nonmetals, along with the halogens; and H, C, P, S and Se being electronegative nonmetals. Se is further recognized as a semiconducting metalloid.[131]
  20. ^ B; Si, Ge; N, P; O, S, Se, Te; nonmetal halogens; and the noble gases[180]
  21. ^ In 2020, high pressure studies and experiments were said to represent "a very active and vigorous research field".[182]
  22. ^ How helium acquired the -ium suffix is explained in the following passage by its discoverer, William Lockyer: "I took upon myself the responsibility of coining the word helium ... I did not know whether the substance ... was a metal like calcium or a gas like hydrogen, but I did know that it behaved like hydrogen [being found in the sun] and that hydrogen, as Dumas had stated, behaved as a metal".[200]
  23. ^ Berzelius, who discovered selenium, thought it had the properties of a metal, combined with those of sulfur.[204]
  24. ^ The Goldhammer-Herzfeld ratio is roughly equal to the cube of the atomic radius divided by the molar volume.[219] More specifically, it is the ratio of the force holding an individual atom's outer electrons in place with the forces on the same electrons from interactions between the atoms in the solid or liquid element. When the interatomic forces are greater than, or equal to, the atomic force, outer electron itinerancy is indicated and metallic behaviour is predicted. Otherwise nonmetallic behaviour is anticipated.[220]
  25. ^ (a) The values are from Aylward and Findlay.[244]
    (b) Weighable amounts of the extremely radioactive elements At (element 85), Fr (87), and elements with an atomic number higher than Es (99), have not been prepared.[245]
    (c) The density values used for At and Fr are theoretical estimates.[246][247]
    (d) Bjerrum classified "heavy metals" as those metals with densities above 7 g/cm3.[248]
    (e) Vernon specified a minimum electronegativity of 1.9 for the metalloids, on the revised Pauling scale.[2]
  26. ^ The quote marks are not found in the source; they are used here to make it clear that the source employs the word nonmetals as a formal term for the subset of chemical elements in question, rather than applying to nonmetals generally.
  27. ^ See also Properties of metals, metalloids and nonmetals, which treats metalloids as a class of their own
  28. ^ Carbon as exfoliated (expanded) graphite,[276] and as carbon nanotube wire;[44] phosphorus as white phosphorus (soft as wax, pliable and can be cut with a knife, at room temperature);[45] sulfur as plastic sulfur;[46] and selenium as selenium wires[47]
  29. ^ Metals have electrical conductivity values of from 6.9×103 S•cm−1 for manganese to 6.3×105 for silver.[278]
  30. ^ Metalloids have electrical conductivity values of from 1.5×10−6 S•cm−1 for boron to 3.9×104 for arsenic.[279]
  31. ^ Unclassified nonmetals have electrical conductivity values of from ca. 1×10−18 S•cm−1 for the elemental gases to 3±4 in graphite.[280]
  32. ^ The nonmetal halogens have electrical conductivity values of from ca. 1×10−18 S•cm−1 for F and Cl to 1.7×10−8 S•cm−1 for iodine.[280][111]
  33. ^ The elemental gases have electrical conductivity values of ca. 1×10−18 S•cm−1.[280]
  34. ^ They always give "compounds less acidic in character than the corresponding compounds of the [typical] nonmetals"[269]
  35. ^ Arsenic trioxide reacts with sulfur trioxide, forming arsenic "sulfate" As2(SO4)3.[291]
  36. ^ CO and N2O are "formally the anhydrides of formic and hyponitrous acid, respectively: CO + H2O → H2CO2 (HCOOH, formic acid); N2O + H2O → H2N2O2 (hyponitrous acid)".[296]
  37. ^ Disodium helide (Na2He) is a compound of helium and sodium that is stable at high pressures above 113 GPa. Argon forms an alloy with nickel, at 140 GPa and close to 1,500 K however at this pressure argon is no longer a noble gas.[305]
  38. ^ Values for the noble gases are from Rahm, Zeng and Hoffmann.[306]



  1. ^ a b c d Larrañaga, Lewis & Lewis 2016, p. 988
  2. ^ a b c d e f g Vernon 2013
  3. ^ Hérold 2006, pp. 149–50
  4. ^ a b c Vernon 2020, p. 220
  5. ^ Luchinskii & Trifonov 1981, pp. 200–220
  6. ^ Jolly 1966, inside cover
  7. ^ Rayner-Canham 2020, p. 212
  8. ^ Glinka 1958, p. 77; Oxtoby, Gillis & Butler 2015, p. I.23
  9. ^ Godovikov & Nenasheva 2020, p. 4
  10. ^ a b Sanderson 1957, p. 229
  11. ^ Morely & Muir 1892, p. 241
  12. ^ a b Kneen, Rogers & Simpson 1972, pp. 218–219
  13. ^ Steudel 2020, p. 43
  14. ^ a b Hill, Holman & Hulme 2017, p. 182: Atomic conductance is the electrical conductivity of one mole of a substance. It is equal to electrical conductivity divided by molar volume.
  15. ^ IUPAC Periodic Table of the Elements
  16. ^ Johnson 2007, p. 13
  17. ^ Bodner & Pardue 1993, p. 354; Cherim 1971, p. 98
  18. ^ Restrepo et al. 2006, p. 411; Thornton & Burdette 2010, p. 86; Hermann, Hoffmann & Ashcroft 2013, pp. 11604‒1‒11604‒5
  19. ^ Mewes et al. 2019; Smits et al. 2020; Florez et al. 2022
  20. ^ a b c d Kneen, Rogers & Simpson 1972, pp. 261–264
  21. ^ Phillips 1973, p. 7
  22. ^ a b c d e f Aylward & Findlay 2008, pp. 6–12
  23. ^ a b Jenkins & Kawamura 1976, p. 88
  24. ^ Carapella 1968, p. 30
  25. ^ Zumdahl & DeCoste 2010, pp. 455, 456, 469, A40
  26. ^ Still 2016, p. 120
  27. ^ Siekierski & Burgess 2002, p. 86
  28. ^ Charlier, Gonze & Michenaud 1994
  29. ^ Taniguchi et al. 1984, p. 867: "... black phosphorus ... [is] characterized by the wide valence bands with rather delocalized nature."; Morita 1986, p. 230; Carmalt & Norman 1998, p. 7: "Phosphorus ... should therefore be expected to have some metalloid properties."; Du et al. 2010. Interlayer interactions in black phosphorus, which are attributed to van der Waals-Keesom forces, are thought to contribute to the smaller band gap of the bulk material (calculated 0.19 eV; observed 0.3 eV) as opposed to the larger band gap of a single layer (calculated ~0.75 eV).
  30. ^ Wiberg 2001, pp. 742
  31. ^ Evans 1966, pp. 124–25
  32. ^ Wiberg 2001, pp. 758
  33. ^ Stuke 1974, p. 178; Donohue 1982, pp. 386–87; Cotton et al. 1999, p. 501
  34. ^ Steudel 1977, p. 240: "... considerable orbital overlap must exist, to form intermolecular, many-center ... [sigma] bonds, spread through the layer and populated with delocalized electrons, reflected in the properties of iodine (lustre, color, moderate electrical conductivity)."; Segal 1989, p. 481: "Iodine exhibits some metallic properties ..."
  35. ^ Wiberg 2001, p. 416; Wiberg is here referring to iodine.
  36. ^ Elliot, A (1929). "The absorption band spectrum of chlorine". Proceedings of the Royal Society A. 123 (792): 629-644(629). doi:10.1098/rspa.1929.0088.
  37. ^ Fox, M (2010). Optical Properties of Solids (2 ed.). New York: Oxford University Press. p. 31. ISBN 978-0-19-957336-3.
  38. ^ Wibaut, JP (1951). Organic Chemistry. New York: Elsevier Publishing Company. p. 33. "Many substances...are colourless and therefore show no selective absorption in the visible part of the spectrum."
  39. ^ Kneen, Rogers & Simpson 1972, pp. 85–86, 237
  40. ^ Salinas 2019, p. 379
  41. ^ Yang 2004, p. 9
  42. ^ Wiberg 2001, pp. 416, 574, 681, 824, 895, 930; Siekierski & Burgess 2002, p. 129
  43. ^ Chung 1987; Godfrin & Lauter 1995
  44. ^ a b Janas, Cabrero-Vilatela & Bulmer 2013
  45. ^ a b Faraday 1853, p. 42; Holderness & Berry 1979, p. 255
  46. ^ a b Partington 1944, p. 405
  47. ^ a b Regnault 1853, p. 208
  48. ^ Herzfeld 1927, pp. 701–705; Edwards 2000, pp. 100–103
  49. ^ Kneen, Rogers & Simpson 1972, pp. 263‒264
  50. ^ Langley & Hattori 2014, p. 214
  51. ^ a b Abbott 1966, p. 18
  52. ^ Brown et al. 2014, p. 237
  53. ^ Ebbing & Wrighton 2007 p. 868
  54. ^ Lidin 1996, pp. 22, 29; 322, 165; 381, 173–174; 12, 147; 157 [B; P; Se; As; I]; Housecroft & Sharpe 2008, p. 472 [I]
  55. ^ Lidin 1996, pp. 52, 58; 386; 140; 361, 365; 372, 376; 403 [C; Si; Ge; S; Sb; Te]; Rochow 1973, p. 1338 [Si]; Sanderson 1967, p. 172 [Ge]; Shkol'nikov 2010, p. 2127 [Sb]; Wiberg 2001, pp. 592 [Te]
  56. ^ Matson & Orbaek 2013, p. 85
  57. ^ Yoder, Suydam & Snavely 1975, p. 58
  58. ^ Young et al. 2018, p. 753
  59. ^ Brown et al. 2014, p. 227
  60. ^ Siekierski & Burgess 2002, pp. 21, 133, 177
  61. ^ Moore 2016; Burford, Passmore & Sanders 1989, p. 54
  62. ^ King & Caldwell 1954, p. 17; Brady & Senese 2009, p. 69
  63. ^ Chemical Abstracts Service 2021
  64. ^ Cockell 2019, p. 210
  65. ^ Emsley 2011, pp. 81, 181; Scott 2014, p. 3
  66. ^ Kneen, Rogers & Simpson 1972, pp. 226, 360
  67. ^ Lee 1996, p. 240
  68. ^ Greenwood & Earnshaw 2002, p. 43
  69. ^ Cressey 2010
  70. ^ Siekierski & Burgess 2002, pp. 24–25
  71. ^ Siekierski & Burgess 2002, p. 23
  72. ^ Petruševski & Cvetković 2018; Grochala 2018
  73. ^ Greenwood & Earnshaw 2002, pp. 27, 1232, 1234
  74. ^ Siekierski & Burgess 2002, pp. 52, 101, 111, 124, 194
  75. ^ Cox 2004, p. 146
  76. ^ a b Vernon 2013, p. 1706
  77. ^ Wiberg 2001, passim
  78. ^ Vernon 2020, p. 222
  79. ^ Atkins & Overton 2010, pp. 377, 389
  80. ^ Moody 1991, p. 391
  81. ^ Rodgers 2012, p. 504; Wulfsberg 2000, p. 726
  82. ^ Stellman 1998, chapter 104–211
  83. ^ Nakao 1992, p. 426–427
  84. ^ Hill & Holman 2000, p. 196
  85. ^ Wiberg 2001, pp. 1761–1762
  86. ^ Young 2006, p. 1285
  87. ^ Encyclopædia Britannica 2021
  88. ^ Royal Society of Chemistry 2021
  89. ^ Chambers & Holliday 1982, pp. 273–274; Bohlmann 1992, p. 213; Jentzsch 2015, p. 247
  90. ^ Vassilakis, Kalemos & Mavridis 2014, p. 1; Hanley & Koga 2018, p. 24; Kaiho 2017, ch. 2, p. 1
  91. ^ Bailar et al. 1989, p. 742
  92. ^ Tshitoyan et al. 2019, pp. 95–98
  93. ^ Russell & Lee 2005, p. 419
  94. ^ Hampel & Hawley 1976, p. 174;
  95. ^ Goodrich 1844, p. 264; The Chemical News 1897, p. 189; Hampel & Hawley 1976, p. 191; Lewis 1993, p. 835; Hérold 2006, pp. 149–50
  96. ^ Tyler 1948, p. 105; Reilly 2002, pp. 5–6
  97. ^ a b Jones 2010, pp. 169–71
  98. ^ Stein 1983, p. 165
  99. ^ Matson & Orbaek 2013, p. 203
  100. ^ Jolly 1966, p. 20
  101. ^ Clugston & Flemming 2000, pp. 100–101, 104–105, 302
  102. ^ Maosheng 2020, p. 962
  103. ^ Mazej 2020
  104. ^ Wiberg 2001, p. 1131
  105. ^ Vernon 2020, p. 229
  106. ^ Cox 2000, pp. 258–259; Möller 2003, p. 173; Trenberth & Smith 2005, p. 864
  107. ^ Emsley 2011, p. 220
  108. ^ Emsley 2011, p. 440
  109. ^ Zhu et al. 2014, pp. 644–648
  110. ^ Wiberg 2001, pp. 4022
  111. ^ a b Greenwood & Earnshaw 2002, p. 804
  112. ^ Rudolph 1973, p. 133: "Oxygen and the halogens in particular ... are therefore strong oxidizing agents."
  113. ^ Daniel & Rapp 1976, p. 55
  114. ^ a b Cotton et al. 1999, p. 554
  115. ^ Woodward et al. 1999, pp. 133–194
  116. ^ Phillips & Williams 1965, pp. 478–479
  117. ^ Moeller et al. 2012, p. 314
  118. ^ Lanford 1959, p. 176
  119. ^ Rayner-Canham 2020, p. 92, 139
  120. ^ Massey 2000, p. 113
  121. ^ Schmedt, Mangstl & Kraus 2012, p. 7847‒7849
  122. ^ Emsley 2011, p. 478
  123. ^ Greenwood & Earnshaw 2002, p. 277
  124. ^ Atkins et al. 2006, p. 320
  125. ^ Greenwood & Earnshaw 2002, p. 482; Berger 1997, p. 86
  126. ^ Moss 1952, pp. 180, 202
  127. ^ a b c d e Cao et al. 2021, pp. 20–21
  128. ^ Challoner 2014, p. 5; Government of Canada 2015; Gargaud et al. 2006, p. 447
  129. ^ Crichton 2012, p. 6; Scerri 2013; Los Alamos National Laboratory 2021
  130. ^ Vernon 2020, p. 218
  131. ^ Wulfsberg 2000, pp. 273–274, 620
  132. ^ Seese & Daub 1985, p. 65
  133. ^ MacKay, MacKay & Henderson 2002, p. 209
  134. ^ Cousins, Davidson & García-Vivó 2013, pp. 11809–11811
  135. ^ a b Wiberg 2001, pp. 255–257
  136. ^ Liptrot 1983, p. 161
  137. ^ Scott & Kanda 1962, p. 153
  138. ^ Taylor 1960, p. 316
  139. ^ a b c d e f g Emsley 2011, passim
  140. ^ Crawford 1968, p. 540
  141. ^ Benner, Ricardo & Carrigan 2018, pp. 167—168: "The stability of the carbon—carbon bond ... has made it the first choice element to scaffold biomolecules. Hydrogen is need for many reasons; at the very least, it terminates C–C chains. Heteroatoms (atoms that are neither carbon nor hydrogen) determine the reactivity of carbon-scaffolded biomolecules. In ... life, these are oxygen, nitrogen and, to a lesser extent, sulfur, phosphorus, selenium, and an occasional halogen."
  142. ^ Zhao, Tu & Chan 2021
  143. ^ Kosanke et al. 2012, p. 841
  144. ^ Wasewar 2021, pp. 322–323
  145. ^ Messler 2011, p. 10
  146. ^ King et al. 1994, p. 1344; Powell & Tims 1974, pp. 189–191
  147. ^ Vernon 2020, pp. 221–223
  148. ^ Rayner-Canham 2020, p. 216
  149. ^ Atkins 2001, pp. 24–25
  150. ^ a b Cox 1997, pp. 130–132; Emsley 2011, passim
  151. ^ National Center for Biotechnology Information 2021
  152. ^ Emsley 2011, p. 113
  153. ^ Greenwood & Earnshaw 2002, p. 270–271
  154. ^ Khan 2001, p. 59
  155. ^ Cox 1997, pp. 130; Emsley 2011, p. 393
  156. ^ Cox 1997, pp. 130; Emsley 2011, pp. 515–516, 518
  157. ^ Boyd 2011, p. 570
  158. ^ Masterton, Hurley & Neth 2011, p. 38
  159. ^ McCue 1963, p. 264
  160. ^ Dingle 2017, p. 101
  161. ^ Hurlbut 1961, p. 132
  162. ^ Barton 2021, p. 200
  163. ^ Shanabrook, Lannin & Hisatsune 1981, pp. 130‒133
  164. ^ Borg & Dienes 1992, p. 26
  165. ^ Wiberg 2001, p. 796
  166. ^ Shang et al. 2021
  167. ^ Tang et al. 2021
  168. ^ Cacace, de Petris & Troiani 2002, pp. 480‒481
  169. ^ Koziel 2002, p. 18
  170. ^ Gusmão, Sofer & Pumera 2017, p. 8052–8053; Berger 1997, p. 84; Vernon 2013, pp. 1704‒1705
  171. ^ Piro et al. 2006, pp. 1276‒1279
  172. ^ Steudel & Eckert 2003, p. 1
  173. ^ Greenwood & Earnshaw 2002, pp. 659–660
  174. ^ Moss 1952, p. 192; Greenwood & Earnshaw 2002, p. 751
  175. ^ Donohue 1982, pp. 48–81
  176. ^ Shiell at al. 2021
  177. ^ Zhao et al. 2017
  178. ^ Donohue 1982, pp. 302–310
  179. ^ Brodsky et al. 1972, p. 609–614
  180. ^ a b Keeler & Wothers 2013, p. 293
  181. ^ Yousuf 1998, p. 425; Elatresh & Bonev 2020
  182. ^ Errandonea 2020, p. 595
  183. ^ Su et al. 2020, pp. 1621–1649
  184. ^ Nelson 1987, p. 732: crust, atmosphere, hydrosphere; Fortescue 2012, pp. 56, 65: biomass
  185. ^ MacKay, MacKay & Henderson 2002, p. 200
  186. ^ Cox 1997, pp. 17, 19
  187. ^ Ostriker & Steinhardt 2001, pp. 46‒53
  188. ^ Höll et al. 2007
  189. ^ Mineral Commodity Summaries 2022 (PDF). U.S. Geological Survey. 2022. pp. 70–71.
  190. ^ Mineral Commodity Summaries 2022 (PDF). U.S. Geological Survey. 2022. pp. 25, 64, 78.
  191. ^ Mineral Commodity Summaries 2022 (PDF). U.S. Geological Survey. 2022. pp. 24, 25, 26, 70, 74, 78, 82, 148, 150, 152, 160, 169.; Kopteva, A; Kalimullin, L; Tcvetkov, P (2021). "Prospects and obstacles for green hydrogen production in Russia". Energies. 14 (3): 1–21(1). doi:10.3390/en14030718.; Oztemel, BH; Salt, I; Salt, Y (2022). "Carbon dioxide utilization: Process simulation of synthetic fuel production from flue gases". Chemical Industry and Chemical Engineering Quarterly: 5. doi:10.2298/CICEQ211025005B.; Neice, A. E.; Zornow, M. H. (2016). "Editorial: Xenon anaesthesia for all, or only a select few?". Anaesthesia. 71 (11): 1259–1272 (1268). doi:10.1111/anae.13569. PMID 27530275. S2CID 46632796.; Howe-Grant, M, ed. (1995). Fluorine Chemistry: A Comprehensive Treatment. New York: John Wiley and Sons. p. 17. ISBN 978-0-471-12031-5.; Dalakov, P; Neuber, E; Herzog, R (2020). "Innovative neon refrigeration unit operating down to 30 K". MATEC Web of Conferences. 324. doi:10.1051/matecconf/20203240 (inactive 2022-09-08).{{cite journal}}: CS1 maint: DOI inactive as of September 2022 (link); Boysen, B; Cristóbal, J; Hilbig, J (2020). "Economic and environmental assessment of water reuse in industrial parks: case study based on a Model Industrial Park". Journal of Water Reuse and Desalination. 10 (4): 475–489. doi:10.2166/wrd.2020.034. S2CID 226335833.; Gardner, AJ; Menon, DK (2018). "Moving to human trials for argon neuroprotection in neurological injury: A narrative review". British Journal of Anaesthesia. 120 (4): 453–468 (455). doi:10.1016/j.bja.2017.10.017. PMID 29452802.; Rajarathnam, GP; assallo, AM (February 2016). The Zinc/bromine Flow Battery: Materials Challenges and Practical Solutions for Technology Advancement. Singapore: Springer. p. 3. ISBN 978-981-287-645-4.; Xia, G-J; Ning, Z-X; Zhu, X-M (2020). "Effect of low-frequency oscillation on plasma focusing in krypton hall thruster". Journal of Propulsion and Power. 36 (1): 25–32. doi:10.2514/1.B37599. S2CID 209940383.;
  192. ^ Chand, H; Kumar, A; Bhumla, P (2022). "Scalable production of ultrathin boron nanosheets from a low-cost precursor". Advanced Materials Interfaces. 9 (23): 22058 (2 of 11). doi:10.1002/admi.202200508. S2CID 250591879.
  193. ^ Berger, LI (1997). Semiconductor Materials. Boca Raton: CRC Press. p. 42. ISBN 978-0-8493-8912-2.
  194. ^ "Mineral Commodity Summaries 1998" (PDF). U.S. Geological Survey. 1998. Retrieved 27 August 2022.
  195. ^ a b Boise State University 2020
  196. ^ Hu, Z; Shen, Z; Yu, JC (2017). "Phosphorus containing materials for photocatalytic hydrogen evolution". Green Chemistry. 19 (3): 588–613 (595). doi:10.1039/C6GC02825J.
  197. ^ Gardner, AJ; Menon, DK (2018). "Moving to human trials for argon neuroprotection in neurological injury: A narrative review". British Journal of Anaesthesia. 120 (4): 453–468 (454). doi:10.1016/j.bja.2017.10.017. PMID 29452802.; Mineral Commodity Summaries 2022 (PDF). U.S. Geological Survey. 2022. p. 25.
  198. ^ National Institute of Standards and Technology 2013
  199. ^ Gaffney & Marley 2017, p. 27
  200. ^ Labinger 2019, p. 305
  201. ^ Emsley 2011, pp. 42–43, 219–220, 263–264, 341, 441–442, 596, 609
  202. ^ Emsley 2011, pp. 84, 128, 180–181, 247
  203. ^ Cook 1923, p. 124
  204. ^ Weeks 1945, p. 161
  205. ^ Emsley 2011, pp. 113, 363, 378, 477, 514–515
  206. ^ Weeks 1945, p. 22; Emsley 2011, p. 40
  207. ^ Klein 1994, p. 168
  208. ^ Lidin 1996, pp. 64‒65
  209. ^ de L'Aunay 1566, p. 7
  210. ^ Homberg 1708, p. 350; vide Kim 2000
  211. ^ de Clave 1641
  212. ^ Schlager & Lauer 2000, p. 370
  213. ^ Strathern 2000, p. 239
  214. ^ Criswell p. 1140
  215. ^ Salzberg 1991, p. 204
  216. ^ Kendall 1811, pp. 298–303
  217. ^ Brande 1821, p. 5
  218. ^ Edwards & Sienko 1983, pp. 691–96
  219. ^ Edwards & Sienko 1983, p. 693
  220. ^ Herzfeld 1927; Edwards 2000, pp. 100–03
  221. ^ Kubaschewski 1949, pp. 931–940
  222. ^ Remy 1956, p. 9
  223. ^ White 1962, p. 106: It makes a ringing sound when struck.
  224. ^ Johnson 1966, pp. 3–4
  225. ^ Horvath 1973, pp. 335–336
  226. ^ Rao & Ganguly 1986
  227. ^ Smith & Dwyer 1991, p. 65: The difference between melting point and boiling point.
  228. ^ a b Herman 1999, p. 702
  229. ^ Suresh & Koga 2001, pp. 5940–5944
  230. ^ Johnson 2007, pp. 15–16
  231. ^ a b Edwards 2010, pp. 941–965
  232. ^ Povh & Rosin 2017, p. 131
  233. ^ Beach 1911
  234. ^ Stott 1956, pp. 100–102
  235. ^ Parish 1977, p. 178
  236. ^ Hare & Bache 1836, p. 310
  237. ^ Chambers 1743: "That which distinguishes metals from all other bodies ... is their heaviness ..."
  238. ^ Edwards 2000, p. 85
  239. ^ Russell & Lee 2005, p. 466
  240. ^ Atkins et al. 2006, pp. 320–21
  241. ^ Zhigal'skii & Jones 2003, p. 66
  242. ^ Emsley 1971, p. 1
  243. ^ Jones 2010, p. 169
  244. ^ Aylward & Findlay 2008, pp. 6–13; 126
  245. ^ Edelstein & Morrs 2009, p. 123
  246. ^ Arblaster, JW, ed. (2018). Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International. p. 604. ISBN 978-1-62708-154-2.
  247. ^ Lavrukhina, AK; Pozdnyakov, AA (1970). Analytical Chemistry of Technetium, Promethium, Astatine, and Francium. Translated by R. Kondor. Ann Arbor: Ann Arbor–Humphrey Science Publishers. p. 269. ISBN 978-0-250-39923-9.
  248. ^ Bjerrum, N (1936). Bjerrum’s Inorganic Chemistry. London: Heinemann.
  249. ^ Johnson 1966, pp. 3–5, 15
  250. ^ Hein, M; Arena, S (2013). Foundations of College Chemistry. Hoboken: John Wiley & Sons. pp. 226, G-6. ISBN 978-1-118-29823-7.
  251. ^ Oderberg 2007, p. 97
  252. ^ Bertomeu-Sánchez, Garcia-Belmar & Bensaude-Vincent 2002, pp. 248–249
  253. ^ Dupasquier 1844, pp. 66–67
  254. ^ Williams 2007, pp. 1550–1561
  255. ^ Wächtershäuser 2014
  256. ^ Hengeveld & Fedonkin, pp. 181–226
  257. ^ Wakeman 1899, p. 562
  258. ^ Fraps 1913, p. 11
  259. ^ Parameswaran at al. 2020, p. 210
  260. ^ Knight 2002, p. 148
  261. ^ Fraústo da Silva & Williams 2001, p. 500
  262. ^ Berzelius 1832, pp. 248–276
  263. ^ The Chemical News 1864, p. 22
  264. ^ Renouf 1901, pp. 268
  265. ^ Vernon 2020, pp. 217–225
  266. ^ Tregarthen 2003, p. 10
  267. ^ Lewis 1993, pp. 28, 827
  268. ^ Lewis 1993, pp. 28, 813
  269. ^ a b c d Rochow 1966, p. 4
  270. ^ Wiberg 2001, p. 780; Emsley 2011, p. 397; Rochow 1966, pp. 23, 84
  271. ^ Kneen, Rogers & Simpson 1972, pp. 321, 404, 436
  272. ^ Kneen, Rogers & Simpson 1972, p. 439
  273. ^ Kneen, Rogers & Simpson 1972, p. 465
  274. ^ Kneen, Rogers & Simpson 1972, p. 308
  275. ^ Wiberg 2001, pp. 505, 681, 781; Glinka 1958, p. 355
  276. ^ Chung 1987, pp. 4190‒4198; Godfrin & Lauter 1995, pp. 216‒218
  277. ^ Wiberg 2001, p. 416
  278. ^ Desai, James & Ho 1984, p. 1160; Matula 1979, p. 1260
  279. ^ Schaefer 1968, p. 76; Carapella 1968, pp. 29‒32
  280. ^ a b c Bogoroditskii & Pasynkov 1967, p. 77; Jenkins & Kawamura 1976, p. 88
  281. ^ Kneen, Rogers & Simpson 1972, p. 264
  282. ^ Rayner-Canham 2018, p. 203
  283. ^ Welcher 2001, p. 3–32: "The elements change from ... metalloids, to moderately active nonmetals, to very active nonmetals, and to a noble gas."
  284. ^ Mackin 2014, p. 80
  285. ^ Johnson 1966, pp. 105–108
  286. ^ Stein 1969, pp. 5396‒5397; Pitzer 1975, pp. 760‒761
  287. ^ Porterfield 1993, p. 336
  288. ^ a b Rao 2002, p. 22
  289. ^ Wells 1984, p. 534
  290. ^ Atkins et al. 2006, pp. 8, 122–123
  291. ^ Wiberg 2001, p. 750
  292. ^ Sidorov 1960, pp. 599‒603
  293. ^ a b c d Puddephatt & Monaghan 1989, p. 59
  294. ^ a b Sanderson 1967, p. 172
  295. ^ a b Mingos 2019, p. 27
  296. ^ House 2008, p. 441
  297. ^ McMillan 2006, p. 823
  298. ^ King 1995, p. 182
  299. ^ Wiberg 2001, p. 399
  300. ^ Kläning & Appelman 1988, p. 3760
  301. ^ Ritter 2011, p. 10
  302. ^ Yamaguchi & Shirai 1996, p. 3
  303. ^ Vernon 2020, p. 223
  304. ^ Woodward et al. 1999, p. 134
  305. ^ Dalton 2019
  306. ^ Rahm, Zeng & Hoffmann 2019, p. 345
  307. ^ Steudel 1977, p. 176


  • Abbott D 1966, An Introduction to the Periodic Table, J. M. Dent & Sons, London
  • Atkins PA 2001, The Periodic Kingdom: A Journey Into the Land of the Chemical Elements, Phoenix, London, ISBN 978-1-85799-449-0
  • Atkins PA et al. 2006, Shriver & Atkins' Inorganic Chemistry, 4th ed., Oxford University Press, Oxford, ISBN 978-0-7167-4878-6
  • Atkins PA & Overton T 2010, Shriver & Atkins' Inorganic Chemistry, 5th ed., Oxford University Press, Oxford, ISBN 978-0-19-923617-6
  • Aylward G and Findlay T 2008, SI Chemical Data, 6th ed., John Wiley & Sons Australia, Milton, ISBN 978-0-470-81638-7
  • Bailar JC et al. 1989, Chemistry, 3rd ed., Harcourt Brace Jovanovich, San Diego, ISBN 978-0-15-506456-0
  • Barton AFM 2021, States of Matter, States of Mind, CRC Press, Boca Raton, ISBN 978-0-7503-0418-4
  • Beach FC (ed.) 1911, The Americana: A universal reference library, vol. XIII, Mel–New, Metalloid, Scientific American Compiling Department, New York
  • Benner SA, Ricardo A & Carrigan MA 2018, "Is there a common chemical model for life in the universe?", in Cleland CE & Bedau MA (eds.), The Nature of Life: Classical and Contemporary Perspectives from Philosophy and Science, Cambridge University Press, Cambridge, ISBN 978-1-108-72206-3
  • Berger LI 1997, Semiconductor Materials, CRC Press, Boca Raton, ISBN 978-0-8493-8912-2
  • Bertomeu-Sánchez JR, Garcia-Belmar A & Bensaude-Vincent B 2002, "Looking for an order of things: Textbooks and chemical classifications in nineteenth century France", Ambix, vol. 49, no. 3, doi:10.1179/amb.2002.49.3.227
  • Berzelius JJ & Bache AD 1832, "An essay on chemical nomenclature, prefixed to the treatise on chemistry", The American Journal of Science and Arts, vol. 22
  • Bodner GM & Pardue HL 1993, Chemistry, An Experimental Science, John Wiley & Sons, New York, ISBN 0-471-59386-9
  • Bogoroditskii NP & Pasynkov VV 1967, Radio and Electronic Materials, Iliffe Books, London
  • Bohlmann R 1992, "Synthesis of halides", in Winterfeldt E (ed.), Heteroatom manipulation, Pergamon Press, Oxford, ISBN 978-0-08-091249-3
  • Boise State University 2020, "Cost-effective manufacturing methods breathe new life into black phosphorus research", Micron School of Materials Science and Engineering, accessed July 9, 2021
  • Borg RG & Dienes GJ 1992, The Physical Chemistry of Solids, Academic Press, Boston, ISBN 978-0-12-118420-9
  • Boyd R 2011, "Selenium stories", Nature Chemistry, vol. 3, doi:10.1038/nchem.1076
  • Brady JE & Senese F 2009, Chemistry: The study of Matter and its Changes, 5th ed., John Wiley & Sons, New York, ISBN 978-0-470-57642-7
  • Brande WT 1821, A Manual of Chemistry, vol. II, John Murray, London
  • Brodsky MH, Gambino RJ, Smith JE Jr & Yacoby Y 1972, "The Raman spectrum of amorphous tellurium", Physica Status Solidi B, vol. 52, doi:10.1002/pssb.2220520229
  • Brown TL et al. 2014, Chemistry: The Central Science, 3rd ed., Pearson Australia: Sydney, ISBN 978-1-4425-5460-3
  • Burford N, Passmore J & Sanders JCP 1989, "The preparation, structure, and energetics of homopolyatomic cations of groups 16 (the chalcogens) and 17 (the halogens), in Liebman JF & Greenberg A, From atoms to polymers : isoelectronic analogies, VCH: New York, ISBN 978-0-89573-711-3
  • Cacace F, de Petris G & Troiani A 2002, "Experimental detection of tetranitrogen", Science, vol. 295, no. 5554, doi:10.1126/science.1067681
  • Cao C et al. 2021, "Understanding periodic and non-periodic chemistry in periodic tables", Frontiers in Chemistry, vol. 8, no. 813, doi:10.3389/fchem.2020.00813
  • Carapella SC 1968, "Arsenic" in Hampel CA (ed.), The Encyclopedia of the Chemical Elements, Reinhold, New York
  • Carmalt CJ & Norman NC 1998, 'Arsenic, Antimony and Bismuth: Some General Properties and Aspects of Periodicity', in NC Norman (ed.), Chemistry of Arsenic, Antimony and Bismuth, Blackie Academic & Professional, London, pp. 1–38, ISBN 0-7514-0389-X
  • Challoner J 2014, The Elements: The New Guide to the Building Blocks of our Universe, Carlton Publishing Group, ISBN 978-0-233-00436-5
  • Chambers E 1743, in "Metal", Cyclopedia: Or an Universal Dictionary of Arts and Sciences (etc.), vol. 2, D Midwinter, London
  • Chambers C & Holliday AK 1982, Inorganic Chemistry, Butterworth & Co., London, ISBN 978-0-408-10822-5
  • Charlier J-C, Gonze X, Michenaud J-P 1994, First-principles Study of the Stacking Effect on the Electronic Properties of Graphite(s), Carbon, vol. 32, no. 2, pp. 289–99, doi:10.1016/0008-6223(94)90192-9
  • Chemical Abstracts Service 2021, CAS REGISTRY database as of November 2, Case #01271182
  • Cherim SM 1971, Chemistry for Laboratory Technicians, Saunders, Philadelphia, ISBN 978-0-7216-2515-7
  • Chung DD 1987, "Review of exfoliated graphite", Journal of Materials Science, vol. 22, doi:10.1007/BF01132008
  • Clugston MJ & Flemming R 2000, Advanced Chemistry, Oxford University Press, Oxford, ISBN 978-0-19-914633-8
  • Cockell C 2019, The Equations of Life: How Physics Shapes Evolution, Atlantic Books, London, ISBN 978-1-78649-304-0
  • Cook CG 1923, Chemistry in Everyday Life: With Laboratory Manual, D Appleton, New York
  • Cotton A et al. 1999, Advanced Inorganic Chemistry, 6th ed., Wiley, New York, ISBN 978-0-471-19957-1
  • Cousins DM, Davidson MG & García-Vivó D 2013, "Unprecedented participation of a four-coordinate hydrogen atom in the cubane core of lithium and sodium phenolates", Chemical Communications, vol. 49, doi:10.1039/C3CC47393G
  • Cox AN (ed.) 2000, Allen's Astrophysical Quantities, 4th ed., AIP Press, New York, ISBN 978-0-387-98746-0
  • Cox PA 1997, The Elements: Their Origins, Abundance, and Distribution, Oxford University Press, Oxford, ISBN 978-0-19-855298-7
  • Cox T 2004, Inorganic Chemistry, 2nd ed., BIOS Scientific Publishers, London, ISBN 978-1-85996-289-3
  • Crawford FH 1968, Introduction to the Science of Physics, Harcourt, Brace & World, New York
  • Crichton R 2012, Biological Inorganic Chemistry: A New Introduction to Molecular Structure and Function, 2nd ed., Elsevier, Amsterdam, ISBN 978-0-444-53783-6
  • Cressey D 2010, "Chemists re-define hydrogen bond", Nature newsblog, accessed August 23, 2017
  • Criswell B 2007, "Mistake of having students be Mendeleev for just a day", Journal of Chemical Education, vol. 84, no. 7, pp. 1140–1144, doi:10.1021/ed084p1140
  • Dalton L 2019, "Argon reacts with nickel under pressure-cooker conditions", Chemical & Engineering News, accessed November 6, 2019
  • Daniel PL & Rapp RA 1976, "Halogen corrosion of metals", in Fontana MG & Staehle RW (eds.), Advances in Corrosion Science and Technology, Springer, Boston, doi:10.1007/978-1-4615-9062-0_2
  • de Clave E 1641, New Philosophical Light of True Principles and Elements of Nature, Olivier Devarennes, Paris, accessed February 24, 2022
  • de L'Aunay L 1566, Responce au discours de maistre Iacques Grevin, docteur de Paris, qu'il a escript contre le livre de maistre Loys de l'Aunay, medecin en la Rochelle, touchant la faculté de l'antimoine (Response to the Speech of Master Jacques Grévin,... Which He Wrote Against the Book of Master Loys de L'Aunay,... Touching the Faculty of Antimony), De l'Imprimerie de Barthelemi Berton, La Rochelle
  • Desai PD, James HM & Ho CY 1984, "Electrical Resistivity of Aluminum and Manganese", Journal of Physical and Chemical Reference Data, vol. 13, no. 4, doi:10.1063/1.555725
  • Dingle A 2017, The Elements: An Encyclopedic Tour of the Periodic Table, Quad Books, Brighton, ISBN 978-0-85762-505-2
  • Donohue J 1982, The Structures of the Elements, Robert E. Krieger, Malabar, Florida, ISBN 978-0-89874-230-5
  • Du Y, Ouyang C, Shi S & Lei M 2010, 'Ab Initio Studies on Atomic and Electronic Structures of Black Phosphorus', Journal of Applied Physics, vol. 107, no. 9, pp. 093718–1–4, doi:10.1063/1.3386509
  • Dupasquier A 1844, Traité élémentaire de chimie industrielle, Charles Savy Juene, Lyon.
  • Ebbing DD & Gammon SD 2007, General Chemistry, 9th ed., Houghton Miffllin, Boston, ISBN 978-0-618-85748-7
  • Edelstein NM & Morrs LR 2009, "Chemistry of the Actinide elements", in Nagy S (ed.), Radiochemistry and Nuclear Chemistry: Volume II, Encyclopedia of Life Support Systems, EOLSS Publishers, Oxford, pp. 118–176, ISBN 978-1-84826-577-6
  • Edwards PP 2000, "What, why and when is a metal?", in Hall N (ed.), The New Chemistry, Cambridge University, Cambridge, pp. 85–114, ISBN 978-0-521-45224-3
  • Edwards PP et al. 2010, "... a metal conducts and a non-metal doesn’t", Philosophical Transactions of the Royal Society A, 2010, vol, 368, no. 1914, doi:10.1098/rsta.2009.0282
  • Edwards PP & Sienko MJ 1983, "On the occurrence of metallic character in the periodic table of the elements", Journal of Chemical Education, vol. 60, no. 9, doi:10.1021/ed060p691, PMID 25666074
  • Elatresh SF & Bonev SA 2020, "Stability and metallization of solid oxygen at high pressure", Physical Chemistry Chemical Physics, vol. 22, no. 22, doi:10.1039/C9CP05267D
  • Emsley J 1971, The Inorganic Chemistry of the Non-metals, Methuen Educational, London, ISBN 978-0-423-86120-4
  • Emsley J 2011, Nature's Building Blocks: An A–Z Guide to the Elements, Oxford University Press, Oxford, ISBN 978-0-19-850341-5
  • Encyclopædia Britannica 2021, Periodic table, accessed September 21, 2021
  • Errandonea D 2020, "Pressure-induced phase transformations," Crystals, vol. 10, doi:10.3390/cryst10070595
  • Evans RC 1966, An Introduction to Crystal Chemistry, 2nd ed., Cambridge University, Cambridge
  • Faraday M 1853, The Subject Matter of a Course of Six Lectures on the Non-metallic Elements, (arranged by John Scoffern), Longman, Brown, Green, and Longmans, London
  • Florez et al. 2022, From the gas phase to the solid state: The chemical bonding in the superheavy element flerovium, The Journal of Chemical Physics, vol. 157, 064304, doi:10.1063/5.0097642
  • Fortescue JAC 2012, Environmental Geochemistry: A Holistic Approach, Springer-Verlag, New York, ISBN 978-1-4612-6047-9
  • Fraps GS 1913, Principles of Agricultural Chemistry, The Chemical Publishing Company, Easton, PA
  • Fraústo da Silva JJR & Williams RJP 2001, The Biological Chemistry of the Elements: The Inorganic Chemistry of Life, 2nd ed., Oxford University Press, Oxford, ISBN 978-0-19-850848-9
  • Gaffney J & Marley N 2017, General Chemistry for Engineers, Elsevier, Amsterdam, ISBN 978-0-12-810444-6
  • Gargaud M et al. (eds.) 2006, Lectures in Astrobiology, vol. 1, part 1: The Early Earth and Other Cosmic Habitats for Life, Springer, Berlin, ISBN 978-3-540-29005-6
  • Glinka N 1958, General chemistry, Sobolev D (trans.), Foreign Languages Publishing House, Moscow
  • Godfrin H & Lauter HJ 1995, "Experimental properties of 3He adsorbed on graphite", in Halperin WP (ed.), Progress in Low Temperature Physics, volume 14, Elsevier Science B.V., Amsterdam, ISBN 978-0-08-053993-5
  • Godovikov AA & Nenasheva N 2020, Structural-chemical Systematics of Minerals, 3rd ed., Springer, Cham, Switzerland, ISBN 978-3-319-72877-3
  • Goodrich BG 1844, A Glance at the Physical Sciences, Bradbury, Soden & Co., Boston
  • Government of Canada 2015, Periodic table of the elements, accessed August 30, 2015
  • Greenwood NN & Earnshaw A 2002, Chemistry of the Elements, 2nd ed., Butterworth-Heinemann, ISBN 978-0-7506-3365-9
  • Grochala W 2018, "On the position of helium and neon in the Periodic Table of Elements", Foundations of Chemistry, vol. 20, pp. 191–207, doi:10.1007/s10698-017-9302-7
  • Gusmão R, Sofer Z & Pumera M 2017, "Black phosphorus rediscovered: From bulk material to monolayers", Angewandte Chemie International Edition, vol. 56, no. 28, doi:10.1002/anie.201610512
  • Hampel CA & Hawley GG 1976, Glossary of Chemical Terms, Van Nostrand Reinhold, New York, ISBN 978-0-442-23238-2
  • Hanley JJ & Koga KT 2018, "Halogens in terrestrial and cosmic geochemical systems: Abundances, geochemical behaviours, and analytical methods" in The Role of Halogens in Terrestrial and Extraterrestrial Geochemical Processes: Surface, Crust, and Mantle, Harlov DE & Aranovich L (eds.), Springer, Cham, ISBN 978-3-319-61667-4
  • Hare RA & Bache F 1836, Compendium of the Course of Chemical Instruction in the Medical Department of the University of Pennsylvania, 3rd ed., JG Auner, Philadelphia
  • Hengeveld R & Fedonkin MA 2007, "Bootstrapping the energy flow in the beginning of life", Acta Biotheoretica, vol. 55, doi:10.1007/s10441-007-9019-4
  • Herman ZS 1999, "The nature of the chemical bond in metals, alloys, and intermetallic compounds, according to Linus Pauling", in Maksić, ZB, Orville-Thomas WJ (eds.), 1999, Pauling's Legacy: Modern Modelling of the Chemical Bond, Elsevier, Amsterdam, doi:10.1016/S1380-7323(99)80030-2
  • Hermann A, Hoffmann R & Ashcroft NW 2013, "Condensed Astatine: Monatomic and metallic", Physical Review Letters, vol. 111, doi:10.1103/PhysRevLett.111.116404
  • Hérold A 2006, "An arrangement of the chemical elements in several classes inside the periodic table according to their common properties", Comptes Rendus Chimie, vol. 9, no. 1, doi:10.1016/j.crci.2005.10.002
  • Herzfeld K 1927, "On atomic properties which make an element a metal", Physical Review, vol. 29, no. 5, doi:10.1103PhysRev.29.701
  • Hill G & Holman J 2000, Chemistry in Context, 5th ed., Nelson Thornes, Cheltenham, ISBN 0-17-448307-4
  • Hill G, Holman J & Hulme PG 2017, Chemistry in Context, 7th ed., Oxford University Press, Oxford, ISBN 978-0-19-839618-5
  • Holderness A & Berry M 1979, Advanced Level Inorganic Chemistry, 3rd ed., Heinemann Educational Books, London, ISBN 978-0-435-65435-1
  • Höll, Kling & Schroll E 2007, "Metallogenesis of germanium—A review", Ore Geology Reviews, vol. 30, nos. 3–4, pp. 145–180, doi:10.1016/j.oregeorev.2005.07.034
  • Homberg W 1708, "Des Essais de Chimie", in Histoire De L'Academie Royale Des Sciences: Avec les Memoires de Mathematique & de Physique, L'Académie, Paris
  • Horvath AL 1973, "Critical temperature of elements and the periodic system", Journal of Chemical Education, vol. 50, no. 5, doi:10.1021/ed050p335
  • House JE 2008, Inorganic Chemistry, Elsevier, Amsterdam, ISBN 978-0-12-356786-4
  • Housecroft CE & Sharpe AG 2008, Inorganic Chemistry, 3rd ed., Prentice-Hall, Harlow, ISBN 978-0-13-175553-6
  • Hurlbut Jr CS 1961, Manual of Mineralogy, 15th ed., John Wiley & Sons, New York
  • IUPAC Periodic Table of the Elements, accessed October 11, 2021
  • Janas D, Cabrero-Vilatela, A & Bulmer J 2013, "Carbon nanotube wires for high-temperature performance", Carbon, vol. 64, pp. 305–314, doi:10.1016/j.carbon.2013.07.067
  • Jenkins GM & Kawamura K 1976, Polymeric Carbons—Carbon Fibre, Glass and Char, Cambridge University Press, Cambridge, ISBN 978-0-521-20693-8
  • Jentzsch AV & Matile S 2015, "Anion transport with halogen bonds", in Metrangolo P & Resnati G (eds.), Halogen Bonding I: Impact on Materials Chemistry and Life Sciences, Springer, Cham, ISBN 978-3-319-14057-5
  • Johnson D (ed.) 2007, Metals and Chemical Change, RSC Publishing, Cambridge, ISBN 978-0-85404-665-2
  • Johnson RC 1966, Introductory Descriptive Chemistry, WA Benjamin, New York
  • Jolly WL 1966, The Chemistry of the Non-metals, Prentice-Hall, Englewood Cliffs, New Jersey
  • Jones BW 2010, Pluto: Sentinel of the Outer Solar System, Cambridge University, Cambridge, ISBN 978-0-521-19436-5
  • Kaiho T 2017, Iodine Made Simple, CRC Press, e-book, doi:10.1201/9781315158310
  • Keeler J & Wothers P 2013, Chemical Structure and Reactivity: An Integrated Approach, Oxford University Press, Oxford, ISBN 978-0-19-960413-5
  • Kendall EA 1811, Pocket encyclopædia, 2nd ed., vol. III, Longman, Hurst, Rees, Orme, and Co., London
  • Khan N 2001, An Introduction to Physical Geography, Concept Publishing, New Delhi, ISBN 978-81-7022-898-1
  • Kim MG 2000, "Chemical analysis and the domains of reality: Wilhelm Homberg's Essais de chimie, 1702–1709", Studies in History and Philosophy of Science Part A, vol. 31, no. 1, pp. 37–69, doi:10.1016/S0039-3681(99)00033-3
  • King RB 1994, Encyclopedia of Inorganic Chemistry, vol. 3, John Wiley & Sons, New York, ISBN 978-0-471-93620-6
  • King RB 1995, Inorganic Chemistry of Main Group Elements, VCH, New York, ISBN 978-1-56081-679-9
  • King GB & Caldwell WE 1954, The Fundamentals of College Chemistry, American Book Company, New York
  • Kläning UK & Appelman EH 1988, "Protolytic properties of perxenic acid", Inorganic Chemistry, vol. 27, no. 21, doi:10.1021/ic00294a018
  • Klein U 1994, "Origin of the concept of chemical compound", Science in Context, no. 7, vol. 2, pp. 163–204, doi:10.1017/s0269889700001666
  • Kneen WR, Rogers MJW & Simpson P 1972, Chemistry: Facts, Patterns, and Principles, Addison-Wesley, London, ISBN 978-0-201-03779-1
  • Knight J 2002, Science of Everyday Things: Real-life chemistry, Gale Group, Detroit, ISBN 9780787656324
  • Kosanke et al. 2012, Encyclopedic Dictionary of Pyrotechnics (and Related Subjects), Part 3 – P to Z, Pyrotechnic Reference Series No. 5, Journal of Pyrotechnics, Whitewater, Colorado, ISBN 978-1-889526-21-8
  • Koziel JA 2002, "Sampling and sample preparation for indoor air analysis", in Pawliszyn J (ed.), Comprehensive Analytical Chemistry, vol. 37, Elsevier Science B.V., Amsterdam, ISBN 978-0-444-50510-1
  • Kubaschewski O 1949, "The change of entropy, volume and binding state of the elements on melting", Transactions of the Faraday Society, vol. 45, doi:10.1039/TF9494500931
  • Labinger JA 2019, "The history (and pre-history) of the discovery and chemistry of the noble gases", in Giunta CJ, Mainz VV & Girolami GS (eds.), 150 Years of the Periodic Table: A Commemorative Symposium, Springer Nature, Cham, Switzerland, ISBN 978-3-030-67910-1
  • Lanford OE 1959, Using Chemistry, McGraw-Hill, New York
  • Langley RH & Hattori H 2014, 1,001 Practice Problems: Chemistry For Dummies, John Wiley & Sons, Hoboken, NJ, ISBN 978-1-118-54932-2
  • Larrañaga MD, Lewis RJ & Lewis RA 2016, Hawley's Condensed Chemical Dictionary, 16th ed., Wiley, Hoboken, New York, ISBN 978-1-118-13515-0
  • Lee JD 1996, Concise Inorganic Chemistry, 5th ed., Blackwell Science, Oxford, ISBN 978-0-632-05293-6
  • Lewis RJ 1993, Hawley's Condensed Chemical Dictionary, 12th ed., Van Nostrand Reinhold, New York, ISBN 978-0-442-01131-4
  • Lidin RA 1996, Inorganic Substances Handbook, Begell House, New York, ISBN 978-0-8493-0485-9
  • Liptrot GF 1983, Modern Inorganic Chemistry, 4th ed., Bell & Hyman, ISBN 978-0-7135-1357-8
  • Los Alamos National Laboratory 2021, Periodic Table of Elements: A Resource for Elementary, Middle School, and High School Students, accessed September 19, 2021
  • Luchinskii GP & Trifonov DN 1981, "Some problems of chemical elements classification and the structure of the periodic system", in Uchenie o Periodichnosti. Istoriya i Sovremennoct, (Russian) Nauka, Moscow
  • MacKay KM, MacKay RA & Henderson W 2002, Introduction to Modern Inorganic Chemistry, 6th ed., Nelson Thornes, Cheltenham, ISBN 978-0-7487-6420-4
  • Mackin M 2014, Study Guide to Accompany Basics for Chemistry, Elsevier Science, Saint Louis, ISBN 978-0-323-14652-4
  • Maosheng M 2020, "Noble gases in solid compounds show a rich display of chemistry with enough pressure", Frontiers in Chemistry, vol. 8, doi:10.3389/fchem.2020.570492
  • Massey AG 2000, Main group chemistry, 2nd ed., John Wiley & Sons, Chichester, ISBN 978-0-471-49039-5
  • Masterton W, Hurley C & Neth E 2011, Chemistry: Principles and Reactions, 7th ed., Brooks/Cole, Belmont, California, ISBN 978-1-111-42710-8
  • Matson M & Orbaek AW 2013, Inorganic Chemistry for Dummies, John Wiley & Sons: Hoboken, ISBN 978-1-118-21794-8
  • Matula RA 1979, "Electrical resistivity of copper, gold, palladium, and silver", Journal of Physical and Chemical Reference Data, vol. 8, no. 4, doi:10.1063/1.555614
  • Mazej Z 2020, "Noble-gas chemistry more than half a century after the first report of the noble-gas compound", Molecules, vol. 25, no. 13, doi:10.3390/molecules25133014, PMID 32630333, PMC 7412050
  • McCue JJ 1963, World of Atoms: An Introduction to Physical Science, Ronald Press, New York
  • McMillan P 2006, "A glass of carbon dioxide", Nature, vol. 441, doi:10.1038/441823a
  • Messler Jr RW 2011, The Essence of Materials for Engineers, Jones and Bartlett Learning, Sudbury, Massachusetts, ISBN 978-0-7637-7833-0
  • Mewes et al. 2019, Copernicium: A relativistic noble liquid, Angewandte Chemie International Edition, vol. 58, pp. 17964–17968, doi:10.1002/anie.201906966
  • Mingos DMP 2019, "The discovery of the elements in the Periodic Table", in Mingos DMP (ed.), The Periodic Table I. Structure and Bonding, Springer Nature, Cham, doi:10.1007/978-3-030-40025-5
  • Moeller T et al. 2012, Chemistry: With Inorganic Qualitative Analysis, Academic Press, New York, ISBN 978-0-12-503350-3
  • Möller D 2003, Luft: Chemie, Physik, Biologie, Reinhaltung, Recht, Walter de Gruyter, Berlin, ISBN 978-3-11-016431-2
  • Moody B 1991, Comparative Inorganic Chemistry, 3rd ed., Edward Arnold, London, ISBN 978-0-7131-3679-1
  • Moore JT 2016, Chemistry for Dummies, 2nd ed., ch. 16, Tracking periodic trends, John Wiley & Sons: Hoboken, ISBN 978-1-119-29728-4
  • Morita A 1986, 'Semiconducting Black Phosphorus', Journal of Applied Physics A, vol. 39, no. 4, pp. 227–42, doi:10.1007/BF00617267
  • Morely HF & Muir MM 1892, Watt's Dictionary of Chemistry, vol. 3, Longman's Green, and Co., London
  • Moss, TS 1952, Photoconductivity in the Elements, Butterworths Scientific, London
  • Nakao Y 1992, "Dissolution of noble metals in halogen–halide–polar organic solvent systems", Journal of the Chemical Society, Chemical Communications, no. 5, doi:10.1039/C39920000426
  • National Center for Biotechnology Information 2021, "PubChem compound summary for CID 402, Hydrogen sulfide", accessed August 31, 2021
  • National Institute of Standards and Technology 2013, SRM 4972 – Radon-222 Emanation Standard, accessed August 1, 2021
  • Nelson PG 1987, "Important elements", Journal of Chemical Education, vol. 68, no. 9, doi:10.1021/ed068p732
  • Oderberg DS 2007, Real Essentialism, Routledge, New York, ISBN 978-1-134-34885-5
  • Ostriker JP & Steinhardt PJ 2001, "The quintessential universe", Scientific American, vol. 284, no. 1, pp. 46–53 PMID 11132422, doi:10.1038/scientificamerican0101-46
  • Oxtoby DW, Gillis HP & Butler LJ 2015, Principles of Modern Chemistry, 8th ed., Cengage Learning, Boston, ISBN 978-1-305-07911-3
  • Parameswaran P et al. 2020, "Phase evolution and characterization of mechanically alloyed hexanary Al16.6Mg16.6Ni16.6Cr16.6Ti16.6Mn16.6 high entropy alloy", Metal Powder Report, vol. 75, no. 4, doi:10.1016/j.mprp.2019.08.001
  • Parish RV 1977, The Metallic Elements, Longman, London, ISBN 978-0-582-44278-8
  • Partington JR 1944, A Text-book of Inorganic Chemistry, 5th ed., Macmillan & Co., London
  • Petruševski VM & Cvetković J 2018, "On the 'true position' of hydrogen in the Periodic Table", Foundations of Chemistry, vol. 20, pp. 251–260, doi:10.1007/s10698-018-9306-y
  • Phillips CSG & Williams RJP 1965, Inorganic Chemistry, vol. 1, Principles and non-metals, Clarendon Press, Oxford
  • Phillips JC 1973, "The chemical structure of solids," in Hannay NB (ed.), Treatise on Solid State Chemistry, vol. 1, Plenum Press, New York, pp. 1–42, ISBN 978-1-4684-2663-2
  • Piro NA et al. 2006, "Triple-bond reactivity of diphosphorus molecules", Science, vol. 313, no. 5791, doi:10.1126/science.1129630, PMID 16946068
  • Pitzer K 1975, "Fluorides of radon and elements 118", Journal of the Chemical Society, Chemical Communications, no. 18, doi:10.1039/C3975000760B
  • Porterfield WW 1993, Inorganic chemistry, Academic Press, San Diego, ISBN 978-0-12-562980-5
  • Povh B & Rosina M 2017, Scattering and Structures: Essentials and Analogies in Quantum Physics, 2nd ed., Springer, Berlin, doi:10.1007/978-3-662-54515-7
  • Powell P & Timms P 1974, The Chemistry of the Non-Metals, Chapman and Hall, London, ISBN 978-0-412-12200-2
  • Puddephatt RJ & Monaghan PK 1989, The Periodic Table of the Elements, 2nd ed., Clarendon Press, Oxford, ISBN 978-0-19-855516-2
  • Rahm M, Zeng T & Hoffmann R 2019, "Electronegativity seen as the ground-state average valence electron binding energy", Journal of the American Chemical Society, vol. 141, no. 1, pp. 342−351, doi:10.1021/jacs.8b10246
  • Rao KY 2002, Structural Chemistry of Glasses, Elsevier, Oxford, ISBN 978-0-08-043958-7
  • Rao CNR & Ganguly PA 1986, "New criterion for the metallicity of elements", Solid State Communications, vol. 57, no. 1, pp. 5–6, doi:10.1016/0038-1098(86)90659-9
  • Rayner-Canham G 2018, "Organizing the transition metals", in Scerri E & Restrepo G, Mendeleev to Oganesson: A multidisciplinary perspective on the periodic table, Oxford University, New York, ISBN 978-0-190-668532
  • Rayner-Canham G 2020, The Periodic Table: Past, Present and Future, World Scientific, New Jersey, ISBN 978-981-121-850-7
  • Regnault MV 1853, Elements of Chemistry, vol. 1, 2nd ed., Clark & Hesser, Philadelphia
  • Reilly C 2002, Metal Contamination of Food, Blackwell Science, Oxford, ISBN 978-0-632-05927-0
  • Remy H 1956, Treatise on Inorganic Chemistry, Anderson JS (trans.), Kleinberg J (ed.), vol. II, Elsevier, Amsterdam
  • Renouf E 1901, "Lehrbuch der anorganischen Chemie", Science, vol. 13, no. 320, doi:10.1126/science.13.320.268
  • Restrepo G, Llanos EJ & Mesa H 2006, "Topological space of the chemical elements and its properties", Journal of Mathematical Chemistry, vol. 39, doi:10.1007/s10910-005-9041-1
  • Ritter SK 2011, "The case of the missing xenon", Chemical & Engineering News, vol. 89, no. 9, ISSN 0009-2347
  • Rochow EG 1966, The Metalloids, DC Heath and Company, Boston
  • Rochow EG 1973, "Silicon", in Bailar JC et al. (eds.), Comprehensive Inorganic Chemistry, vol. 1, Pergamon Press, Oxford, ISBN 978-0-08-015655-2
  • Rodgers GE 2012, Descriptive Inorganic, Coordination, and Solid State Chemistry, 3rd ed., Brooks/Cole, Belmont, California, ISBN 978-0-8400-6846-0
  • Royal Society of Chemistry 2021, Periodic Table: Non-metal, accessed September 3, 2021
  • Rudolph J 1973, Chemistry for the Modern Mind, Macmillan, New York
  • Russell AM & Lee KL 2005, Structure-Property Relations in Nonferrous Metals, Wiley-Interscience, New York, ISBN 0-471-64952-X
  • Salinas JT 2019 Exploring Physical Science in the Laboratory, Moreton Publishing, Englewood, Colorado, ISBN 978-1-61731-753-8
  • Salzberg HW 1991, From Caveman to Chemist: Circumstances and Achievements, American Chemical Society, Washington, DC, ISBN 0-8412-1786-6
  • Sanderson RT 1957, "An electronic distinction between metals and nonmetals", Journal of Chemical Education, vol. 34, no. 5, doi:10.1021/ed034p229
  • Sanderson RT 1967, Inorganic Chemistry, Reinhold, New York
  • Scerri E (ed.) 2013, 30-Second Elements: The 50 Most Significant Elements, Each Explained In Half a Minute, Ivy Press, London, ISBN 978-1-84831-616-4
  • Schaefer JC 1968, "Boron" in Hampel CA (ed.), The Encyclopedia of the Chemical Elements, Reinhold, New York
  • Schlager N & Lauer J (eds.) 2000, Science and Its Times: 1700–1799, volume 4 of Science and its times: Understanding the social significance of scientific discovery, Gale Group, ISBN 978-0-7876-3932-7
  • Schmedt auf der Günne J, Mangstl M & Kraus F 2012, "Occurrence of difluorine F2 in nature—In situ proof and quantification by NMR spectroscopy", Angewandte Chemie International Edition, vol. 51, no. 31, doi:10.1002/anie.201203515
  • Scott D 2014, Around the World in 18 Elements, Royal Society of Chemistry, e-book, ISBN 978-1-78262-509-4
  • Scott EC & Kanda FA 1962, The Nature of Atoms and Molecules: A General Chemistry, Harper & Row, New York
  • Seese WS & Daub GH 1985, Basic Chemistry, 4th ed., Prentice-Hall, Englewood Cliffs, NJ, ISBN 978-0-13-057811-2
  • Segal BG 1989, Chemistry: Experiment and Theory, 2nd ed., John Wiley & Sons, New York, ISBN 0-471-84929-4
  • Shanabrook BV, Lannin JS & Hisatsune IC 1981, "Inelastic light scattering in a onefold-coordinated amorphous semiconductor", Physical Review Letters, vol. 46, no. 2, 12 January, doi:10.1103/PhysRevLett.46.130
  • Shang et al. 2021, "Ultrahard bulk amorphous carbon from collapsed fullerene", Nature, vol. 599, pp. 599–604, doi:10.1038/s41586-021-03882-9
  • Sherwin E & Weston GJ 1966, Chemistry of the Non-metallic Elements, Pergamon Press, Oxford
  • Shiell et al. 2021, "Bulk crystalline 4H-silicon through a metastable allotropic transition", Physical Review Letters, vol. 26, p 215701, doi:10.1103/PhysRevLett.126.215701
  • Shkol’nikov EV 2010, "Thermodynamic characterization of the amphoterism of oxides M2O3 (M = As, Sb, Bi) and their hydrates in aqueous media, Russian Journal of Applied Chemistry, vol. 83, no. 12, pp. 2121–2127, doi:10.1134/S1070427210120104
  • Sidorov TA 1960, "The connection between structural oxides and their tendency to glass formation", Glass and Ceramics, vol. 17, no. 11, doi:10.1007BF00670116
  • Siekierski S & Burgess J 2002, Concise Chemistry of the Elements, Horwood Press, Chichester, ISBN 978-1-898563-71-6
  • Smith A & Dwyer C 1991, Key Chemistry: Investigating Chemistry in the Contemporary World: Book 1: Materials and Everyday Life, Melbourne University Press, Carlton, Victoria, ISBN 978-0-522-84450-4
  • Smits et al. 2020, Oganesson: A noble gas element that is neither noble nor a gas, Angewandte Chemie International Edition, vol. 59, pp. 23636–23640, doi:10.1002/anie.202011976
  • Stein L 1969, "Oxidized radon in halogen fluoride solutions", Journal of the American Chemical Society, vol. 19, no. 19, doi:10.1021/ja01047a042
  • Stein L 1983, "The chemistry of radon", Radiochimica Acta, vol. 32, doi:10.1524/ract.1983.32.13.163
  • Stellman JM (ed.) 1998, Encyclopaedia of Occupational Health and Safety, vol. 4, 4th ed., International Labour Office, Geneva, ISBN 978-92-2-109817-1
  • Steudel R 1977, Chemistry of the Non-metals: With an Introduction to atomic Structure and Chemical Bonding, Walter de Gruyter, Berlin, ISBN 978-3-11-004882-7
  • Steudel R & Eckert B 2003, "Solid sulfur allotropes", in Steudel R (ed.), Elemental Sulfur and Sulfur-rich Compounds I, Springer-Verlag, Berlin, ISBN 978-3-540-40191-9
  • Steudel R 2020, Chemistry of the Non-metals: Syntheses - Structures - Bonding - Applications, in collaboration with D Scheschkewitz, Berlin, Walter de Gruyter, doi:10.1515/9783110578065
  • Still B 2016 The secret life of the periodic table, Cassell, London, ISBN 978-1-84403-885-5
  • Stott RWA 1956, Companion to Physical and Inorganic Chemistry, Longmans, Green and Co, London
  • Stuke J 1974, 'Optical and electrical properties of selenium', in RA Zingaro & WC Cooper (eds), Selenium, Van Nostrand Reinhold, New York, pp. 174
  • Strathern P 2000, Mendeleyev's dream: The Quest for the Elements, Hamish Hamilton, London, ISBN 978-0-8412-1786-7
  • Su et al. 2020, "Advances in photonics of recently developed Xenes", Nanophotonics, vol. 9, no. 7, doi:10.1515/nanoph-2019-0561
  • Suresh CH & Koga NA 2001, "A consistent approach toward atomic radii”, Journal of Physical Chemistry A, vol. 105, no. 24. doi:10.1021/jp010432b
  • Tang et al. 2021, "Synthesis of paracrystalline diamond", Nature, vol. 599, pp. 605–610, doi:10.1038/s41586-021-04122-w
  • Taniguchi M, Suga S, Seki M, Sakamoto H, Kanzaki H, Akahama Y, Endo S, Terada S & Narita S 1984, 'Core-exciton induced resonant photoemission in the covalent semiconductor black phosphorus', Solid State Communications, vo1. 49, no. 9, pp. 867–7, doi:10.1016/0038-1098(84)90441-1
  • Taylor MD 1960, First Principles of Chemistry, Van Nostrand, Princeton
  • The Chemical News and Journal of Physical Science 1864, "Notices of books: Manual of the Metalloids", vol. 9, p. 22
  • The Chemical News and Journal of Physical Science 1897, "Notices of books: A Manual of Chemistry, Theoretical and Practical", by WA Tilden", vol. 75, pp. 188–189
  • Thornton BF & Burdette SC 2010, "Finding eka-iodine: Discovery priority in modern times", Bulletin for the history of chemistry, vol. 35, no. 2, accessed September 14, 2021
  • Tregarthen L 2003, Preliminary Chemistry, Macmillan Education: Melbourne, ISBN 978-0-7329-9011-4
  • Trenberth KE & Smith L 2005, "The mass of the atmosphere: A constraint on global analyses", Journal of Climate, vol. 18, no. 6, doi:10.1175/JCLI-3299.1
  • Tshitoyan et al. 2019, "Unsupervised word embeddings capture latent knowledge from materials science literature", Nature, vol. 571, doi:10.1038/s41586-019-1335-8
  • Tyler PM 1948, From the Ground Up: Facts and Figures of the Mineral Industries of the United States, McGraw-Hill, New York
  • Vassilakis AA, Kalemos A & Mavridis A 2014, "Accurate first principles calculations on chlorine fluoride ClF and its ions ClF±", Theoretical Chemistry Accounts, vol. 133, no. 1436, doi:10.1007/s00214-013-1436-7
  • Vernon R 2013, "Which elements are metalloids?", Journal of Chemical Education, vol. 90, no. 12, 1703‒1707, doi:10.1021/ed3008457
  • Vernon R 2020, "Organising the metals and nonmetals", Foundations of Chemistry, vol. 22, doi:10.1007/s10698-020-09356-6 (open access)
  • Wächtershäuser G 2014, "From chemical invariance to genetic variability", in Weigand W and Schollhammer P (eds.), Bioinspired Catalysis: Metal Sulfur Complexes, Wiley-VCH, Weinheim, doi:10.1002/9783527664160.ch1
  • Wakeman TH 1899, "Free thought—Past, present and future", Free Thought Magazine, vol. 17
  • Wasewar KL 2021, "Intensifying approaches for removal of selenium", in Devi et al. (eds), Selenium contamination in water, John Wiley & Sons, Hoboken, pp. 319–355, ISBN 978-1-119-69354-3
  • Weeks ME 1945, Discovery of the Elements, 5th ed., Journal of Chemical Education, Easton, Pennsylvania
  • Welcher SH 2001, High marks: Regents Chemistry Made Easy, 2nd ed., High Marks Made Easy, New York, ISBN 978-0-9714662-4-1
  • Wells AF 1984, Structural Inorganic Chemistry, 5th ed., Clarendon Press, Oxford, ISBN 978-0-19-855370-0
  • White JH 1962, Inorganic Chemistry: Advanced and Scholarship Levels, University of London Press, London
  • Wiberg N 2001, Inorganic Chemistry, Academic Press, San Diego, ISBN 978-0-12-352651-9
  • Williams RPJ 2007, "Life, the environment and our ecosystem", Journal of Inorganic Biochemistry, vol. 101, nos. 11–12, doi:10.1016/j.jinorgbio.2007.07.006
  • Woodward et al. 1999, "The electronic structure of metal oxides", In Fierro JLG (ed.), Metal Oxides: Chemistry and Applications, CRC Press, Boca Raton, ISBN 1-4200-2812-X
  • Wulfsberg G 1987, Principles of Descriptive Chemistry, Brooks/Cole, Belmont CA, ISBN 978-0-534-07494-4
  • Wulfsberg G 2000, Inorganic Chemistry, University Science Books, Sausalito, California, ISBN 978-1-891389-01-6
  • Yamaguchi M & Shirai Y 1996, "Defect structures", in Stoloff NS & Sikka VK (eds.), Physical Metallurgy and Processing of Intermetallic Compounds, Chapman & Hall, New York, ISBN 978-1-4613-1215-4
  • Yang J 2004, 'Theory of thermal conductivity', in Tritt TM (ed.), Thermal Conductivity: Theory, Properties, and Applications, Kluwer Academic/Plenum Publishers, New York, pp. 1–20, ISBN 978-0-306-48327-1,
  • Yoder CH, Suydam FH & Snavely FA 1975, Chemistry, 2nd ed, Harcourt Brace Jovanovich, New York, ISBN 978-0-15-506470-6
  • Young JA 2006, "Iodine", Journal of Chemical Education, vol. 83, no. 9, doi:10.1021/ed083p1285
  • Young et al. 2018, General Chemistry: Atoms First, Cengage Learning: Boston, ISBN 978-1-337-61229-6
  • Yousuf M 1998, "Diamond anvil cells in high-pressure studies of semiconductors", in Suski T & Paul W (eds.), High Pressure in Semiconductor Physics II, Semiconductors and Semimetals, vol. 55, Academic Press, San Diego, ISBN 978-0-08-086453-2
  • Zhao J, Tu Z & Chan SH 2021, Carbon corrosion mechanism and mitigation strategies in a proton exchange membrane fuel cell (PEMFC): A review, Journal of Power Sources, vol. 488, #229434, doi:10.1016/j.jpowsour.2020.229434
  • Zhao Z, Zhang H, Kim D. et al. 2017, "Properties of the exotic metastable ST12 germanium allotrope", Nature Communications, vol. 8, article no. 13909, doi:10.1038/ncomms13909, PMID 28045027, PMC 5216117
  • Zhigal'skii GP & Jones BK 2003, The Physical Properties of Thin Metal Films, Taylor & Francis, London, ISBN 978-0-415-28390-8
  • Zhu et al. 2014, "Reactions of xenon with iron and nickel are predicted in the Earth's inner core", Nature Chemistry, vol. 6, doi:10.1038/nchem.1925, PMID 24950336
  • Zumdahl SS & DeCoste DJ 2010, Introductory Chemistry: A Foundation, 7th ed., Cengage Learning, Mason, Ohio, ISBN 978-1-111-29601-8

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