View source for Chemistry:Nonmetal

{{short description|Chemical element that mostly lacks the characteristics of a metal}}
{{About|chemical elements
|nonmetallic substances
|materials science
}}
[[File:Nonmetals in the periodic table.png|thumb|upright=0.85|

<hr style="color:white;background-color:white">
Extract of [[Chemistry:Periodic table|periodic table]] showing how often each element is classified as a nonmetal:
<hr style="color:white;background-color:white">
 {{nobreak|{{colorbox|#CCFFCC|'''14'''}} effectively always}}{{#tag:ref|H; N; O, S; F, Cl, Br, I; He, Ne, Ar, Kr, Xe, Rn.<ref name="Larrañaga">Larrañaga, Lewis & Lewis 2016, p. 988</ref>|group=n}}

 {{nobreak|{{colorbox|#FFFF99|'''3'''}} frequently}}{{#tag:ref|C; P; Se.<ref name="Larrañaga"/> On the other hand, these three elements were counted as [[Chemistry:Metalloid|metalloid]]s in a survey of 194 lists of metalloids, 16, 10, and 46 times respectively.<ref name="Vernon2013">Vernon 2013</ref> |group=n}}

 {{nobreak|{{colorbox|#FF9999|'''6'''}} sometimes ([[Chemistry:Metalloid|metalloid]]s)}}{{#tag:ref|B; Si, Ge; As, Sb; Te.<ref name="Hérold2006">Hérold 2006, pp. 149–50; Vernon 2020, p. 220</ref>|group=n}}
<hr style="color:white;background-color:white">
Nearby metals are shown in a gray font.{{#tag:ref|Al, Ga, In, Tl; Sn, Pb; Bi; Po; At.|group=n}}
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There is no precise definition of a nonmetal; which elements are counted as such varies.
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Hydrogen is usually in group 1 (as in the [[Chemistry:Periodic table|full table]] below) but can be in group 17 (as in the extract above).{{#tag:ref|Hydrogen has historically been placed over one or more of lithium, boron,<ref name="Luchinskii">Luchinskii & Trifonov 1981, pp. 200–220</ref> carbon, or fluorine;<ref name="Jol">Jolly 1966, inside cover</ref> or over no group at all; or over all main groups simultaneously, and therefore may or may not be adjacent to other nonmetals.<ref>Rayner-Canham 2020, p. 212</ref>|group=n}}

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|alt=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 [[Chemistry:Metal|metal]]s are aluminium, gallium, indium, thallium, tin, lead, bismuth, polonium, and astatine.]]

A '''nonmetal''' is a [[Chemistry:Chemical element|chemical element]] that, in the broadest sense of the term, has a relatively low [[Physics:Density|density]] and high [[Chemistry:Electronegativity|electronegativity]]; they range from colorless gases (like [[Chemistry:Hydrogen|hydrogen]]) to shiny solids (like [[Chemistry:Carbon|carbon]], as [[Chemistry:Graphite|graphite]]). They are usually poor [[Physics:Thermal conduction|conductors of heat]] and [[Physics:Electrical conductor|electricity]], and brittle or crumbly when solid due to their [[Physics:Electron|electron]]s having low mobility. In contrast, metals are good conductors and most are easily flattened into sheets and [[Physics:Ductility|drawn into wires]] since their electrons are generally free-moving. Nonmetal atoms tend to attract electrons in [[Chemistry:Chemical reaction|chemical reaction]]s and to form [[Chemistry:Acid|acid]]ic compounds.

Two nonmetals, hydrogen and [[Chemistry:Helium|helium]], make up [[Chemistry:Abundance of the chemical elements#Universe|about 99%]] of [[Physics:Baryonic matter|ordinary matter]] in the [[Astronomy:Observable universe|observable universe]] by mass. Five nonmetallic elements, hydrogen, carbon, [[Chemistry:Nitrogen|nitrogen]], [[Chemistry:Oxygen|oxygen]] and [[Chemistry:Silicon|silicon]], make up most of the [[Earth:Earth's crust|Earth's crust]], [[Earth:Atmosphere of Earth|atmosphere]], oceans and [[Biology:Biosphere|biosphere]].

The distinctive properties of nonmetallic elements allow for specific applications that often cannot be fulfilled by metallic elements alone. Living organisms are composed almost entirely of the nonmetals hydrogen, oxygen, carbon, and nitrogen. Nonmetallic elements are important to industries ranging from electronics and energy storage to agriculture and chemical production.

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, and which of these borderline cases are counted as nonmetals varies depending on the classification criteria used. Generally, from 14 to 23 elements are recognized as nonmetals.

==Definition and applicable elements==
A nonmetal is a [[Chemistry:Chemical element|chemical element]] that, in the broadest sense of the term, has a relatively low [[Physics:Density|density]] and high [[Chemistry:Electronegativity|electronegativity]].<ref name="Hein"/> More generally they are deemed to lack a preponderance of metallic properties such as luster or shininess; the capacity to be flattened into a sheet or [[Physics:Ductility|drawn into a wire]]; good [[Physics:Thermal conductivity|thermal]] and [[Physics:Electrical conductivity|electrical conductivity]]; and the capacity to form a [[Chemistry:Base|basic]] (rather than [[Chemistry:Acid|acidic]]) [[Chemistry:Oxide|oxide]].<ref>Glinka 1958, p. 77; Oxtoby, Gillis & Butler 2015, p. I.23</ref> Since there is no rigorous definition of a nonmetal,<ref>Godovikov & Nenasheva 2020, p. 4; Sanderson 1957, p. 229; Morely & Muir 1892, p. 241</ref> 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.<ref name=Kneen218>Kneen, Rogers & Simpson 1972, pp. 218–219</ref>{{#tag:ref|Metallic or nonmetallic character is usually taken to be indicated by one property rather than two or more properties.|group=n}}

Although Steudel,<ref>Steudel 2020, p. 43</ref>{{#tag:ref| Steudel's monograph is an updated translation of the fifth German edition of 2013, incorporating the literature up to Spring 2019.|group=n}} in 2020, recognised twenty-three elements as nonmetals, any such list is open to challenge.<ref name="Larrañaga"/> The fourteen elements that are almost always recognized as nonmetals are [[Chemistry:Hydrogen|hydrogen]], [[Chemistry:Oxygen|oxygen]], [[Chemistry:Nitrogen|nitrogen]], and [[Chemistry:Sulfur|sulfur]]; the highly reactive halogens [[Chemistry:Fluorine|fluorine]], [[Chemistry:Chlorine|chlorine]], [[Chemistry:Bromine|bromine]], and [[Chemistry:Iodine|iodine]]; and the noble gases [[Chemistry:Helium|helium]], [[Chemistry:Neon|neon]], [[Chemistry:Argon|argon]], [[Chemistry:Krypton|krypton]], [[Chemistry:Xenon|xenon]], and [[Chemistry:Radon|radon]], as listed in ''Hawley’s Condensed Chemical Dictionary.''<ref name="Larrañaga"/> While [[Chemistry:Carbon|carbon]], [[Chemistry:Phosphorus|phosphorus]] and [[Chemistry:Selenium|selenium]] were included as nonmetals, it had earlier been reported that these three elements were instead sometimes counted as metalloids.<ref name="Vernon2013"/> The elements commonly recognized as metalloids ([[Chemistry:Boron|boron]]; [[Chemistry:Silicon|silicon]] and [[Chemistry:Germanium|germanium]]; [[Chemistry:Arsenic|arsenic]] and [[Chemistry:Antimony|antimony]]; and [[Chemistry:Tellurium|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.<ref>Hill & Holman 2017, p. 162</ref> At other times they are counted as nonmetals in light of their predominately nonmetallic (weakly [[Chemistry:Acid|acid]]ic) chemistry.<ref>Vernon 2020, p. 220; Rochow 1966, p. 4</ref>

Of the 118 known elements,<ref>IUPAC Periodic Table of the Elements</ref> no more than about 20% are regarded as nonmetals.<ref>Johnson 2007, p. 13</ref> The status of a few elements is less certain. [[Chemistry:Astatine|Astatine]], the fifth halogen, is often ignored on account of its rarity and intense [[Physics:Radioactive decay|radioactivity]];<ref>Bodner & Pardue 1993, p. 354; Cherim 1971, p. 98</ref> theory and experimental evidence suggest it is a metal.<ref>Restrepo et al. 2006, p. 411; Thornton & Burdette 2010, p. 86; Hermann, Hoffmann & Ashcroft 2013, pp. 11604‒1‒11604‒5</ref> The superheavy elements [[Chemistry:Copernicium|copernicium]] (element&nbsp;112), [[Chemistry:Flerovium|flerovium]] (114), and [[Chemistry:Oganesson|oganesson]] (118) may turn out to be nonmetals. {{as of|2023|April}} their status has not been confirmed.<ref>Mewes et al. 2019; Smits et al. 2020; Florez et al. 2022</ref>

==General properties==
:''Properties noted in this section refer to the elements in their most stable forms in ambient conditions''

===Physical===
{{multiple image|perrow=3|total_width=320|caption_align=center
| align = right
| image_style = border:none;
|image1=Boron R105.jpg
 |alt1=Several dozen small angular stone like shapes, grey with scattered silver flecks and highlights.
 |caption1= Boron in its β-rhombohedral phase
|image2=Graphite2.jpg
 |alt2=A shiny grey-black cuboid nugget with a rough surface.
 |caption2= Metallic appearance of [[Chemistry:Carbon|carbon]] as [[Chemistry:Graphite|graphite]]
|image3=Liquid oxygen in a beaker 4.jpg
 |alt3=A pale blue liquid in a clear beaker
 |caption3= Blue color of [[Physics:Liquid oxygen|liquid oxygen]]
|image4=Liquid fluorine tighter crop.jpg
 |alt4=A glass tube, is inside a larger glass tube, has some clear yellow liquid in it
 |caption4= Pale yellow liquid fluorine in a [[Physics:Cryogenics|cryogenic bath]]
|image5=Sulfur-sample.jpg
 |alt5=Yellow powdery chunks
 |caption5= [[Chemistry:Sulfur|Sulfur]] as a yellow powder
|image6=Bromine_in_a_vial.png
 |alt6=A small capped jar a quarter filled with a very dark liquid
 |caption6= Liquid [[Chemistry:Bromine|bromine]] at room temperature
|image7=Iodinecrystals.JPG
 |caption7= Metallic appearance of [[Chemistry:Iodine|iodine]] under white light
 |alt7=Shiny violet-black colored crystalline shards.
|image8=An acrylic cube specially prepared for element collectors containing an ampoule filled with liquefied xenon.JPG
 |alt8=A partly filled ampoule containing a colorless liquid
 |caption8= Liquefied xenon
| header = {{font|size=100%|font=Sans-serif|text=Variety in color and form<br>of some nonmetallic elements}}
}}

About half of nonmetallic elements are gases; most of the rest are shiny solids. Bromine, the only liquid, is so [[Chemistry:Volatility|volatile]] that it is usually topped by a layer of its fumes; sulfur is the only colored solid nonmetal.{{#tag:ref|Solid iodine has a silvery metallic appearance under white light at room temperature.<ref>Koenig 1962, p. 108</ref> It volatizes at ordinary and higher temperatures, passing from solid to gas; its vapours are violet-colored.<ref>Tidy 1887, pp. 107–108</ref>|group=n}} The fluid nonmetals have very low densities, [[Physics:Melting point|melting point]]s, and [[Physics:Boiling point|boiling point]]s, and are poor conductors of heat and electricity.<ref name="Kneen">Kneen, Rogers & Simpson 1972, pp. 261–264</ref> The solid elements have low densities, are brittle or crumbly with low mechanical and structural strength,<ref>Phillips 1973, p. 7</ref> and are poor to good conductors.{{#tag:ref|The solid nonmetals have thermal conductivity values of from 0.27 W m<sup>–1</sup> K<sup>–1</sup> for sulfur to 2,000 for carbon cf. 6.3 for [[Chemistry:Neptunium|neptunium]] to 429 for [[Chemistry:Silver|silver]], both metals;<ref name="A&W">Aylward & Findlay 2008, pp. 6–12</ref> electrical conductivity values range from 10<sup>−18</sup> S•cm<sup>−1</sup> for sulfur<ref name="A&W"/> to 3 × 10<sup>4</sup> in graphite<ref name="Jenkins">Jenkins & Kawamura 1976, p. 88</ref> or 3.9 × 10<sup>4</sup> for [[Chemistry:Arsenic|arsenic]]<ref>Carapella 1968, p. 30</ref> cf. 0.69 × 10<sup>4</sup> for [[Chemistry:Manganese|manganese]] to 63 × 10<sup>4</sup> for [[Chemistry:Silver|silver]], metals both.<ref name="A&W"/>|group=n}}

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 [[Physics:Valence electron|outer electron]]s 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, the outer electrons are expected to become free to move between atoms, and metallic properties are predicted. Otherwise nonmetallic properties are expected.<ref>Edwards 2000, pp. 100, 102–103; Herzfeld 1927, pp. 701–705</ref>

Those nonmetals existing as discrete atoms (xenon, for example) or molecules (oxygen, sulfur, and bromine, for example) have low melting and boiling points, and many are gases at room temperature, since they are held together by weak London dispersion forces acting between their atoms or molecules.<ref>Zumdahl & DeCoste 2010, pp. 455, 456, 469, A40; Earl & Wilford 2021, p. 3-24</ref> Nonmetals that form giant structures, such as chains of up to 1,000 atoms (selenium),<ref>Still 2016, p. 120</ref> sheets (carbon as graphite, for example),<ref>Wiberg 2001, pp. 780</ref> or three-dimensional lattices (silicon, for example),<ref>Wiberg 2001, pp. 824, 785</ref> have higher melting and boiling points, and are all solids, as it takes more energy to overcome their stronger [[Chemistry:Covalent bond|covalent bond]]s.<ref>Earl & Wilford 2021, p. 3-24</ref> Those closer to the left side of the periodic table, or further down a column, often have some weak [[Physics:Delocalized electron|metallic interactions]] between their molecules, chains, or layers, consistent with their proximity to the metals; this occurs in boron,<ref>Siekierski & Burgess 2002, p. 86</ref> carbon,<ref>Charlier, Gonze & Michenaud 1994</ref> phosphorus,<ref>Taniguchi et al. 1984, p. 867: "...&nbsp;black phosphorus&nbsp;... [is] characterized by the wide valence bands with rather delocalized nature."; Morita 1986, p. 230; Carmalt & Norman 1998, p. 7: "Phosphorus&nbsp;... 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&nbsp;eV; observed 0.3&nbsp;eV) as opposed to the larger band gap of a single layer (calculated ~0.75&nbsp;eV).</ref> arsenic,<ref>Wiberg 2001, pp. 742</ref> selenium,<ref>Evans 1966, pp. 124–25</ref> antimony,<ref>Wiberg 2001, pp. 758</ref> tellurium<ref>Stuke 1974, p. 178; Donohue 1982, pp. 386–87; Cotton et al. 1999, p. 501</ref> and iodine.<ref>Steudel 1977, p. 240: "...&nbsp;considerable orbital overlap must exist, to form intermolecular, many-center&nbsp;... [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&nbsp;..."</ref>

Nonmetallic elements are either shiny, colored, or colorless. The shiny appearance of boron, graphitic carbon, silicon, black phosphorus, germanium, arsenic, selenium, antimony, tellurium, and iodine is a result of their structures featuring varying degrees of delocalised (free-moving) electrons that scatter incoming visible light.<ref>Wiberg 2001, p. 416; Wiberg is here referring to iodine.</ref> The colored nonmetals (sulfur, fluorine, chlorine, bromine) absorb some colors (wavelengths) and transmit the complementary or opposite colors. In the case of chlorine, for example, Elliot writes that its "familiar yellow-green colour...is due to a broad region of absorption in the violet and blue regions of the spectrum".<ref>Elliot 1929, p. 629</ref>{{#tag:ref|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.<ref>Fox 2010, p. 31</ref>|group=n}}

For the colorless nonmetals (hydrogen, nitrogen, oxygen, and the noble gases), their electrons are held sufficiently strongly such that no absorption happens in the visible part of the spectrum, and all visible light is transmitted.<ref>Wibaut 1951, p. 33: "Many substances...are colourless and therefore show no selective absorption in the visible part of the spectrum."</ref>

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 [[Physics:Plasticity|plasticity]] (malleability, ductility) are ordinarily associated with the presence of free-moving and uniformly distributed electrons in metals<ref>Kneen, Rogers & Simpson 1972, pp. 85–86, 237</ref> the electrons in nonmetals typically lack such mobility.<ref>Salinas 2019, p. 379</ref> Among the nonmetallic elements, good electrical and thermal conductivity is seen only in carbon, arsenic, and antimony.{{#tag:ref|Thermal conductivity values for metals range from 6.3 W m<sup>–1</sup> K<sup>–1</sup> for [[Chemistry:Neptunium|neptunium]] to 429 for [[Chemistry:Silver|silver]]; cf. antimony 24.3, arsenic 50, and carbon 2000;<ref name="A&W"/> electrical conductivity values of metals range from 0.69 S•cm<sup>−1</sup> × 10<sup>4</sup> for [[Chemistry:Manganese|manganese]] to 63 × 10<sup>4</sup> for [[Chemistry:Silver|silver]]; cf. carbon 3 × 10<sup>4</sup>,<ref name="Jenkins"/> arsenic 3.9 × 10<sup>4</sup> and antimony 2.3 × 10<sup>4</sup>.<ref name="A&W"/>|group=n}} Good thermal conductivity otherwise occurs only in boron, silicon, phosphorus, and germanium;<ref name="A&W"/> such conductivity is transmitted though vibrations of the crystalline lattices of these elements.<ref>Yang 2004, p. 9</ref> Moderate electrical conductivity is evidenced in boron, silicon, phosphorus, germanium, selenium, tellurium, and iodine.{{#tag:ref|These elements being [[Physics:Semiconductor|semiconductor]]s.<ref>Wiberg 2001, pp. 416, 574, 681, 824, 895, 930; Siekierski & Burgess 2002, p. 129</ref>|group=n}} Plasticity occurs under limited circumstances in carbon, as exfoliated ([[Chemistry:Graphite#Expanded graphite|expanded) graphite]]<ref>Chung 1987; Godfrin & Lauter 1995</ref> and as [[Physics:Carbon nanotube|carbon nanotube]] wire;<ref name="Janas">Janas, Cabrero-Vilatela & Bulmer 2013</ref> phosphorus as white phosphorus (soft as wax, pliable and can be cut with a knife, at room temperature);<ref name="Holderness 1979, p. 255">Faraday 1853, p. 42; Holderness & Berry 1979, p. 255</ref> sulfur as plastic sulfur;<ref name="ReferenceE">Partington 1944, p. 405</ref> and selenium as selenium wires, drawn from the molten form.<ref name="ReferenceF">Regnault 1853, p. 208</ref>

===Chemical===
{|class="wikitable floatright" style="line-height: 1.3; font-size: 95%; margin-top:1.2em; margin-left:20px"
|+ Some chemistry-based typical<br/>differences between metals and nonmetals<ref>Kneen, Rogers & Simpson 1972, pp. 263‒264</ref>
|-
! Aspect !! Metals !! Nonmetals
|-
| [[Chemistry:Electronegativity|Electronegativity]]
|Lower than nonmetals,<br>with some exceptions<ref>Langley & Hattori 2014, p. 214</ref>
|Relatively high
|-
| rowspan=4 | Chemical<br/>bonding
|-
| Seldom form<br>[[Chemistry:Covalent bond|covalent bond]]s
| Frequently form<br>covalent bonds
|-
| Metallic bonds ([[Chemistry:Alloy|alloy]]s)<br/>between metals
| Covalent bonds<br/>between nonmetals
|-
| colspan=2 | Ionic bonds between nonmetals and metals
|-
| Oxidation<br/>states
| Positive
| Negative or positive
|-
| [[Chemistry:Oxide|Oxide]]s
| [[Chemistry:Base|Basic]] in lower oxides;<br/>increasingly acidic<br/>in higher oxides
| [[Chemistry:Acid|Acid]]ic;<br>never basic<ref name="ReferenceC">Abbott 1966, p. 18</ref> 
|-
| In [[Chemistry:Aqueous solution|aqueous<br/>solution]]<ref>Brown et al. 2014, p. 237</ref>
| Exist as cations
| Exist as anions<br/>or [[Chemistry:Oxyanion|oxyanion]]s
|}

Nonmetals have relatively high values of electronegativity<ref name="Hein">Hein & Arena 2013, pp. 226, G-6</ref> and tend to form acidic compounds. For example, the solid nonmetals (including metalloids) react with [[Chemistry:Nitric acid|nitric acid]] to form either an acid, or an oxide that has acidic properties predominating.{{#tag:ref|Acids are formed by boron, phosphorus, selenium, arsenic, iodine;<ref>Lidin 1996, pp. 22, 29; 322, 165; 381, 173–174; 12, 147; 157 [B; P; Se; As; I]; Housecroft & Sharpe 2008, p. 472 [I]</ref> oxides by carbon, silicon, germanium, sulfur, antimony, and tellurium.<ref>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]</ref>|group=n}}

They tend to gain or share electrons when they react, unlike metals which tend to donate electrons. Given the stability of the [[Physics:Electron configuration|electron configuration]]s of the noble gases (which have full outer [[Physics:Electron shell|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 [[Octet rule#Other rules|duet]] and [[Octet rule|octet rule]]s of thumb (and for metals there is a less rigorously predictive [[18-electron rule|18-electron rule]]).<ref>Matson & Orbaek 2013, p. 85</ref>

Nonmetals further mostly have higher [[Physics:Ionization energy|ionization energies]], [[Physics:Electron affinity|electron affinities]], and standard reduction potentials than metals. In general, the higher these values are (including electronegativity) the more nonmetallic the element is.<ref>Yoder, Suydam & Snavely 1975, p. 58</ref>

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 [[Physics:Proton|proton]]s in the [[Physics:Atomic nucleus|atomic nucleus]] increases.<ref>Young et al. 2018, p. 753</ref> There is an associated reduction in atomic radius<ref>Brown et al. 2014, p. 227</ref> as the increasing nuclear charge draws the outer electrons closer to the core.<ref>Siekierski & Burgess 2002, pp. 21, 133, 177</ref> 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 [[Physics:Ion|ion]]s whereas nonmetals tend to gain those same electrons due to their stronger nuclear charge, and form negatively charged ions or polarized atoms.<ref>Moore 2016; Burford, Passmore & Sanders 1989, p. 54</ref>

The number of compounds formed by nonmetals is vast.<ref>King & Caldwell 1954, p. 17; Brady & Senese 2009, p. 69</ref> The first 10 places in a "top 20" table of elements most frequently encountered in 895,501,834 compounds, as listed in the [[Organization:Chemical Abstracts Service|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.<ref>Chemical Abstracts Service 2021</ref> A few examples of nonmetal compounds are: [[Chemistry:Boric acid|boric acid]] ({{chem|||H|3||BO|3}}), used in ceramic glazes;<ref>Emsley 2011, pp. 81</ref> [[Chemistry:Selenocysteine|selenocysteine]] ({{chem|||C|3||H|7||NO|2||Se}}), the 21st [[Chemistry:Amino acid|amino acid]] of life;<ref>Cockell 2019, p. 210</ref> [[Chemistry:Phosphorus sesquisulfide|phosphorus sesquisulfide]] (P<sub>4</sub>S<sub>3</sub>), in [[Engineering:Match|strike anywhere matches]];<ref>Scott 2014, p. 3</ref> and [[Engineering:Teflon|teflon]] ({{Chem|||(C|2||F|4|}})''<sub>n</sub>''),<ref>Emsley 2011, p. 184</ref> as used in non-stick coatings for pans and other cookware.

===Complications===
[[File:PT_blocks_and_1st_rows.png|thumb|right|upright=1.6|Periodic table highlighting the first row of each block.{{#tag:ref|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.|group=n}} 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.|alt=H and He are in the first row of the s-block. B through Ne take up the first row of the p-block. Sc through Zn occupy the first row of the d-block. La to Yb make up the first row of the f block. The elements within scope of the article are hydrogen, helium, boron, carbon, nitrogen, oxygen, fluorine, neon, silicon, phosphorus, sulfur, chlorine, argon, germanium, arsenic, selenium, bromine, krypton, antimony, tellurium, iodine, xenon, and radon.]]
[[File:EN values of chalcogens.png|thumb|upright=0.8|Electronegativity values of the group 16 [[Chemistry:Chalcogen|chalcogen]] elements showing a W-shaped alternation or secondary periodicity going down the group|alt=A graph with a vertical electronegativity axis and a horizontal atomic number axis. The five elements plotted are O, S, Se, Te and Po. The electronegativity of Se looks too high, and causes a bump in what otherwise be a smooth curve.]]

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 [[Chemistry:Periodic table#Further manifestations of periodicity|secondary periodicity]] or non-uniform periodic trends going down most of the p-block groups,<ref>Kneen, Rogers & Simpson 1972, pp. 226, 360</ref> and unusual oxidation states in the heavier nonmetals.

====First row anomaly====
Starting with hydrogen, the [[Physics:Kainosymmetry|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.<ref>Lee 1996, p. 240</ref> 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.<ref>Greenwood & Earnshaw 2002, p. 43</ref> A hydrogen atom in a molecule can form a second, weaker, bond with an atom or group of atoms in another molecule. According to Cressey such bonding, "helps give snowflakes their hexagonal symmetry, binds [[Biology:DNA|DNA]] into a double helix; shapes the three-dimensional forms of [[Biology:Protein|protein]]s; and even raises water's boiling point high enough to make a decent cup of tea."<ref>Cressey 2010</ref>

Hydrogen and helium, and boron to neon, have unusually small atomic radii. This occurs because the 1s and 2p subshells have no inner analogues (that is, 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.<ref name="S&B">Siekierski & Burgess 2002, pp. 24–25</ref> Ionization energies and electronegativities among these elements are consequently higher than would otherwise be expected, having regard to [[Chemistry:Periodic trends|periodic trends]]. The small atomic radii of carbon, nitrogen, and oxygen facilitate the formation of [[Chemistry:Double bond|double]] or [[Chemistry:Triple bond|triple]] bonds.<ref>Siekierski & Burgess 2002, p. 23</ref>

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.<ref>Petruševski & Cvetković 2018; Grochala 2018</ref>

====Secondary periodicity====
Immediately after the first row of [[Chemistry:Block (periodic table)#d-block|d-block]] metals, scandium to zinc, the 3d electrons in the [[Chemistry:Block (periodic table)#p-block|p-block]] elements—that is, gallium (a metal), germanium, arsenic, selenium, and bromine—are not as effective at [[Physics:Shielding effect|shielding]] the increased positive nuclear charge. A similar effect accompanies the appearance of fourteen f-block metals between [[Chemistry:Barium|barium]] and [[Chemistry:Lutetium|lutetium]], ultimately resulting in [[Chemistry:Lanthanide contraction|smaller than expected atomic radii]] for the elements from [[Chemistry:Hafnium|hafnium]] (Hf) onwards.<ref>Greenwood & Earnshaw 2002, pp. 27, 1232, 1234</ref> 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.<ref>Siekierski & Burgess 2002, pp. 52, 101, 111, 124, 194</ref>

====Unusual oxidation states====
The larger atomic radii of the heavier group 15–18 nonmetals enable higher bulk coordination numbers, and result in lower electronegativity values that better tolerate higher positive charges. The elements involved are thereby able to exhibit [[Chemistry:Oxidation state|oxidation state]]s other than the lowest for their group (that is, 3, 2, 1, or 0), for example in [[Chemistry:Phosphorus pentachloride|phosphorus pentachloride]] (PCl<sub>5</sub>), [[Chemistry:Sulfur hexafluoride|sulfur hexafluoride]] (SF<sub>6</sub>), [[Chemistry:Iodine heptafluoride|iodine heptafluoride]] (IF<sub>7</sub>), and [[Chemistry:Xenon difluoride|xenon difluoride]] (XeF<sub>2</sub>).<ref>Cox 2004, p. 146</ref>{{clear}}

==Subclasses {{anchor|Classes}}==
[[File:XPT extract.png|thumb|Modern periodic table extract showing nonmetal subclasses. H is usually shown in group 1 but can instead be in group 17.{{#tag:ref|Noble gases: He, Ne, Ar, Kr, Xe, Rn; Halogen nonmetals: 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.|group=n}}
<hr style="color:white;background-color:white">
{{nowrap|† moderately strong oxidising agent}}
{{nowrap|‡ strong oxidising agent}}{{#tag:ref|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.<ref name="V1706">Vernon 2013, p. 1706</ref> The remaining reactive nonmetallic elements have giant covalent structures, but for H which is a diatomic gas.<ref>Wiberg 2001, passim</ref>
<hr style="color:white;background-color:white">
The single dagger nonmetals N, S and iodine are somewhat hobbled as "strong" nonmetals.
<hr style="color:white;background-color:white">
While N has a high electronegativity, it is a reluctant anion former,<ref>Vernon 2020, p. 222</ref> and a pedestrian oxidizing agent unless combined with a more active nonmetal like O or F.<ref>Atkins & Overton 2010, pp. 377, 389</ref>
<hr style="color:white;background-color:white">S reacts in the cold with alkalic and [[Chemistry:Post-transition metal|post-transition metal]]s, and Cu, Ag and Hg,<ref>Moody 1991, p. 391</ref> 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.<ref>Rodgers 2012, p. 504; Wulfsberg 2000, p. 726</ref>
<hr style="color:white;background-color:white">Iodine is sufficiently corrosive to cause lesions resembling thermal burns, if handled without suitable protection,<ref>Stellman 1998, chapter&nbsp;104–211</ref> and [[Chemistry:Tincture of iodine|tincture of iodine]] will smoothly dissolve Au.<ref>Nakao 1992, p. 426–427</ref> That said, while "F, Cl and Br will all oxidize Fe<sup>2+</sup> (aq) to Fe<sup>3+</sup>(aq){{nbsp}}... iodine{{nbsp}}... is such a [relatively] weak oxidizing agent that it cannot remove electrons from Fe(II) ions to form Fe(III) ions."<ref>Hill & Holman 2000, p. 196</ref> Thus, for the reaction X<sub>2</sub> + 2e<sup>−</sup> → 2X<sup>−</sup>(aq) the reduction potentials are F +2.87 V; Cl +1.36; Br +1.09; I +0.54. Here Fe<sup>3+</sup> + e<sup>−</sup> → Fe<sup>3+</sup> +0.77.<ref>Wiberg 2001, pp. 1761–1762</ref> Thus F<sub>2</sub>, Cl<sub>2</sub> and Br<sub>2</sub> will oxidize Fe<sup>2+</sup> to Fe<sup>3+</sup> but Fe<sup>3+</sup> will oxidize I<sup>−</sup> to I<sub>2</sub>. Iodine has previously been referred to as a moderately strong oxidizing agent.<ref>Young 2006, p. 1285</ref>|group=n}}|alt=N, S and I are shown as moderately strong oxidizing agents; O, F, Cl and Br are relatively strong oxidizing agents.]]

[[Chemistry:List of alternative nonmetal classes|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".<ref>Encyclopædia Britannica 2021</ref> The [[Organization:Royal Society of Chemistry|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.<ref>Royal Society of Chemistry 2021</ref>

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;<ref name="Matson"/>
* a set of chemically strong halogen elements—fluorine, chlorine, bromine and iodine—sometimes referred to as nonmetal halogens<ref>Chambers & Holliday 1982, pp. 273–274; Bohlmann 1992, p. 213; Jentzsch 2015, p. 247</ref> or halogen nonmetals<ref>Kernion 2019, p. 191; Cao et al. 2021, pp. 20–21; Hussain et al. 2023</ref> (the term used here) or stable halogens;<ref>Vassilakis, Kalemos & Mavridis 2014, p. 1; Hanley & Koga 2018, p. 24; Kaiho 2017, ch.&nbsp;2, p. 1</ref> 
* a set of unclassified nonmetals, including elements such as hydrogen, carbon, nitrogen, and oxygen, with no widely recognized collective name;{{#tag:ref|Varying configurations of these nonmetals have been referred to as, for example, basic nonmetals,<ref>Williams 2007, pp. 1550–1561: H, C, N, P, O, S</ref> bioelements,<ref>Wächtershäuser 2014, p. 5: H, C, N, P, O, S, Se</ref> central nonmetals,<ref>Hengeveld & Fedonkin, pp. 181–226: C, N, P, O, S</ref> CHNOPS,<ref>Wakeman 1899, p. 562</ref> essential elements,<ref>Fraps 1913, p. 11: H, C, Si, N, P, O, S, Cl</ref> "non-metals",<ref>Parameswaran at al. 2020, p. 210: H, C, N, P, O, S, Se</ref>{{#tag:ref|The quote marks are not found in the source; they are used here to make it clear that the source employs the word ''non-metals'' as a formal term for the subset of chemical elements in question, rather than applying to nonmetals generally.|group=n}} orphan nonmetals,<ref>Knight 2002, p. 148: H, C, N, P, O, S, Se</ref> or redox nonmetals.<ref>Fraústo da Silva & Williams 2001, p. 500: H, C, N, O, S, Se</ref>|group=n}} and
* the chemically weak nonmetallic metalloids<ref name="Bailar">Bailar et al. 1989, p. 742</ref> sometimes considered to be nonmetals and sometimes not.{{#tag:ref|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".<ref>Tshitoyan et al. 2019, pp. 95–98</ref>|group=n}}

Since the metalloids occupy "frontier territory",<ref>Russell & Lee 2005, p. 419</ref> 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<ref>Hampel & Hawley 1976, p. 174;</ref> or as a sub-class of nonmetals.<ref>Goodrich 1844, p. 264; ''The Chemical News'' 1897, p. 189; Hampel & Hawley 1976, p. 191; Lewis 1993, p. 835; Hérold 2006, pp. 149–50</ref> Other authors count some of them as metals, for example arsenic and antimony, due to their similarities to [[Chemistry:Heavy metals|heavy metals]].<ref>Tyler 1948, p. 105; Reilly 2002, pp. 5–6</ref>{{#tag:ref|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{{nbsp}}... 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".<ref name="Jones">Jones 2010, pp. 169–71</ref>|group=n}}
Metalloids are here treated as nonmetals in light of their chemical behavior,<ref name="Bailar"/> and for comparative purposes.

Aside from the metalloids, some boundary fuzziness and overlapping (as occurs with classification schemes generally),<ref name="Jones"/> can be discerned among the other nonmetal subclasses. Carbon, phosphorus, selenium, and 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.<ref>Stein 1983, p. 165</ref>

=== Noble gases ===
{{main|Chemistry:Noble gas}}
[[File:Argon ice 1.jpg|thumb|A small (about 2 cm long) piece of rapidly melting argon ice|alt=a glass tube, held upside down by some tongs, has a clear-looking ice-like plug in it which is slowly melting judging from the clear drops falling out of the open end of the tube]]
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.<ref name="Matson">Matson & Orbaek 2013, p. 203</ref>

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.<ref>Jolly 1966, p. 20</ref> That is why they are all gases under [[Standard conditions for temperature and pressure|standard conditions]], even those with [[Physics:Atomic mass|atomic mass]]es larger than many normally solid elements.<ref>Clugston & Flemming 2000, pp. 100–101, 104–105, 302</ref>

Chemically, the noble gases have relatively high ionization energies, nil or negative electron affinities, and high to very high electronegativities. Compounds of the noble gases number in the hundreds, and the list continues to grow,<ref>Maosheng 2020, p. 962</ref> with most of these involving oxygen or fluorine combining with either krypton, xenon or radon.<ref>Mazej 2020</ref>

In periodic table terms, an analogy can be drawn between the [[Chemistry:Noble gas|noble gas]]es and [[Chemistry:Noble metal|noble metal]]s (such as platinum and gold) which are similarly reluctant to combine with other elements.<ref>Wiberg 2001, p. 1131</ref> As a further example, xenon, in the +8 oxidation state, forms a pale yellow explosive oxide, [[Chemistry:Xenon tetroxide|XeO<sub>4</sub>]], while [[Chemistry:Osmium|osmium]], another noble metal, forms a yellow, strongly oxidizing oxide,<ref>Thompson 2004</ref> [[Chemistry:Osmium tetroxide|OsO<sub>4</sub>]]. There are parallels, too, in the formulas of the oxyfluorides: XeO<sub>2</sub>F<sub>4</sub> and OsO<sub>2</sub>F<sub>4</sub>, and XeO<sub>3</sub>F<sub>2</sub> and OsO<sub>3</sub>F<sub>2</sub>.<ref>Vernon 2020, p. 229</ref>

About 10<sup>15</sup> tonnes of noble gases are present in the Earth's atmosphere.<ref>Cox 2000, pp. 258–259; Möller 2003, p. 173; Trenberth & Smith 2005, p. 864</ref> Additionally, [[Chemistry:Natural gas|natural gas]] is found to be as much as 7% Helium.<ref>Emsley 2011, p. 220</ref> Radon diffuses out of rocks, where it is formed during the natural [[Physics:Decay chain|decay sequence]] of [[Chemistry:Uranium|uranium]] and [[Chemistry:Thorium|thorium]].<ref>Emsley 2011, p. 440</ref> The Earth's core may contain about 10<sup>13</sup> tons of xenon, in the form of stable XeFe<sub>3</sub> and XeNi<sub>3</sub> 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."<ref>Zhu et al. 2014, pp. 644–648</ref>

=== Halogen nonmetals ===
[[File:Fluorite-cflo06x.jpg|thumb|A cluster of purple fluorite {{chem|CaF|2}}, the most common fluorine mineral, between two quartzes. It is the main source of fluorine for commercial uses.<ref>Emsley 2011, p. 181</ref>|alt=a cluster of purple crystals flanked to either side by some white crystals which themselves have a sprinkling of brown, translucent crystals on their sides]]

While the halogen nonmetals are markedly reactive and corrosive elements, they can be found in such mundane compounds as [[Medicine:Toothpaste|toothpaste]] ([[Chemistry:Sodium fluoride|NaF]]); ordinary table salt (NaCl); swimming pool disinfectant ([[Chemistry:Sodium bromide|NaBr]]); or food supplements ([[Biology:Potassium iodide|KI]]). The word "halogen" means "[[Chemistry:Salt|salt]] former".<ref>Wiberg 2001, pp. 4022</ref>

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<ref name="V1706"/> solid. Electrically, the first three are [[Physics:Insulator (electricity)|insulator]]s while iodine is a semiconductor (along its planes).<ref name="Greenwood 2002, p. 804">Greenwood & Earnshaw 2002, p. 804</ref>

Chemically, they have high ionization energies, electron affinities, and electronegativity values, and are mostly relatively strong [[Chemistry:Oxidizing agent|oxidizing agent]]s.<ref>Rudolph 1973, p. 133: "Oxygen and the halogens in particular{{nbsp}}... are therefore strong oxidizing agents."</ref> Manifestations of this status include their corrosive nature.<ref name="Daniel">Daniel & Rapp 1976, p. 55</ref> All four exhibit a tendency to form predominately [[Physics:Ionic compound|ionic compound]]s with metals<ref name="Cotton">Cotton et al. 1999, p. 554</ref> whereas the remaining nonmetals, bar oxygen, tend to form predominately covalent compounds with metals.{{#tag:ref|Metal oxides are usually ionic.<ref>Woodward et al. 1999, pp. 133–194</ref> On the other hand, oxides of metals with high oxidation states are usually either polymeric or covalent.<ref>Phillips & Williams 1965, pp. 478–479</ref> A polymeric oxide has a linked structure composed of multiple repeating units.<ref>Moeller et al. 2012, p. 314</ref>|group=n}} The reactive and strongly electronegative nature of the halogen nonmetals represents the epitome of nonmetallic character.<ref name="Lanford">Lanford 1959, p. 176</ref>

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.<ref>Rayner-Canham 2020, p. 92, 139</ref> Most of the alkali metals, as if in imitation of the halogen nonmetals, are known [[Chemistry:Alkalide|to form –1 anions]] (something that rarely occurs among metals).<ref>Massey 2000, p. 113</ref>

The halogen nonmetals are found in salt-related minerals. Fluorine occurs in [[Chemistry:Fluorite|fluorite]] (CaF<sub>2</sub>), a widespread mineral. Chlorine, bromine, and iodine are found in [[Earth:Brine mining|brines]]. Exceptionally, a 2012 study reported the presence of 0.04% native fluorine ({{chem|F|2}}) by weight in [[Physics:Antozonite|antozonite]], attributing these [[Earth:Inclusion (mineral)|inclusions]] as a result of radiation from the presence of tiny amounts of uranium.<ref>Schmedt, Mangstl & Kraus 2012, p. 7847‒7849</ref>

=== Metalloids ===
{{main|Chemistry:Metalloid}}
[[File:Realgar-229713.jpg|thumb|A crystal of [[Chemistry:Realgar|realgar]], also known as "ruby sulphur" or "ruby of arsenic", an arsenic sulfide mineral As<sub>4</sub>S<sub>4</sub>. The two elements involved each have a predominately nonmetallic chemistry.<ref>Bailar, Moeller & Kleinberg 1965, p.&nbsp;477; Mee 1964, p.&nbsp;153</ref>|alt=a cluster of bright cherry-red crystals]]

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 [[Chemistry:Dividing line between metals and nonmetals|dividing line between metals and nonmetals]] shown on some tables.<ref name="Vernon2013"/>

They are brittle and poor-to-good conductors of heat and electricity. Boron, silicon, germanium, and tellurium are semiconductors. Arsenic and antimony have the [[Physics:Electronic band structure|electronic structure]]s of [[Physics:Semimetal|semimetal]]s, although both have less stable semiconducting forms.<ref name="Vernon2013"/>

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.<ref name="Vernon2013"/>

In periodic-table terms, to the left of the weakly nonmetallic metalloids are an indeterminate set of weakly metallic metals (such as [[Chemistry:Tin|tin]], [[Chemistry:Lead|lead]] and [[Chemistry:Bismuth|bismuth]])<ref>Masterton, Hurley & Neth 2011, p. 38</ref> sometimes referred to as post-transition metals.<ref>McCue 1963, p. 264</ref> Dingle explains the situation this way:
{{blockquote|...&nbsp;with 'no-doubt' metals on the far left of the table, and no-doubt non-metals on the far right{{nbsp}}... the gap between the two extremes is bridged first by the poor ([[Chemistry:Post-transition metal|post-transition]]) metals, and then by the metalloids—which, perhaps by the same token, might collectively be renamed the 'poor non-metals'.<ref>Dingle 2017, p. 101</ref>}}

The metalloids tend to be found in forms combined with oxygen, sulfur, or (in the case of tellurium) gold or silver.<ref name="occur"/> Boron is found in boron-oxygen [[Physics:Borate|borate]] minerals, including in volcanic spring waters. Silicon occurs in the silicon-oxygen mineral [[Chemistry:Silica|silica]] (sand). Germanium, arsenic, and antimony are mainly found as components of [[Chemistry:Sulfide|sulfide]] ores. Tellurium occurs in [[Chemistry:Telluride mineral|telluride mineral]]s of gold or silver. Native forms of arsenic, antimony, and tellurium have been reported.<ref>Hurlbut 1961, p. 132</ref>

=== Unclassified nonmetals ===
{{anchor|Unclassified nonmetal|right}}
[[File:Selenium black (cropped).jpg|thumb|right|[[Chemistry:Selenium|Selenium]] conducts electricity around 1,000 times better when light falls on it, a property used in light-sensing applications.<ref>Emsley 2011, p. 478</ref>|alt=A small glass jar filled with small dull grey concave buttons. The pieces of selenium look like tiny mushrooms without their stems.]]

After the nonmetallic elements are classified as either noble gases, halogens, or metalloids, 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 [[Physics:Semimetal|semimetal]] along its planes<ref>Greenwood & Earnshaw 2002, p. 277</ref> and a semiconductor in a direction perpendicular to its planes;<ref>Atkins et al. 2006, p. 320</ref> phosphorus and selenium are semiconductors;<ref>Greenwood & Earnshaw 2002, p. 482; Berger 1997, p. 86</ref> and hydrogen, nitrogen, oxygen, and sulfur are insulators.{{#tag:ref|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.<ref>Moss 1952, pp. 180, 202</ref>|group=n}}

These elements are generally regarded as being too diverse to merit a collective classification,<ref name="Cao 2021, pp. 20">Cao et al. 2021, pp. 20–21</ref> and have been referred to as ''other nonmetals'',<ref>Challoner 2014, p. 5; Government of Canada 2015; Gargaud et al. 2006, p. 447</ref> or more plainly as ''nonmetals'', located between the ''metalloids'' and the ''halogens''.<ref>Crichton 2012, p. 6; Scerri 2013; Los Alamos National Laboratory 2021</ref> Consequently, their chemistry tends to be taught disparately, according to their four respective [[Chemistry:Group (periodic table)|periodic table groups]].<ref>Vernon 2020, p. 218</ref> 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.{{#tag:ref|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.<ref>Wulfsberg 2000, pp. 273–274, 620</ref>|group=n}}

Hydrogen, in particular, behaves in some respects like a metal and in others like a nonmetal.<ref>Seese & Daub 1985, p. 65</ref> Like a metal, it can (first) lose its single electron;<ref>MacKay, MacKay & Henderson 2002, p. 209</ref> it can stand in for alkali metals in typical alkali metal structures;<ref>Cousins, Davidson & García-Vivó 2013, pp. 11809–11811</ref> and is capable of forming alloy-like [[Physics:Hydride|hydride]]s, featuring metallic bonding, with some [[Chemistry:Transition metal|transition metal]]s.<ref name="Wiberg255–257">Wiberg 2001, pp. 255–257</ref> 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.<ref>Liptrot 1983, p. 161</ref> It does this by way of forming a covalent or ionic bond<ref name="Wiberg255–257"/> or, if it has lost its electron, attaching itself to a lone pair of electrons.<ref>Scott & Kanda 1962, p. 153</ref>

Some or all of these nonmetals nevertheless have several shared properties. Most of them, being less reactive than the halogens,<ref>Taylor 1960, p. 316</ref> can occur naturally in the environment.<ref name="Emsley"/> They have prominent [[Astronomy:CHNOPS|biological]]<ref>Crawford 1968, p. 540; Benner, Ricardo & Carrigan 2018, pp. 167—168: "The stability of the carbon—carbon bond{{nbsp}}... has made it the first choice element to scaffold biomolecules. Hydrogen is needed 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{{nbsp}}... life, these are oxygen, nitrogen and, to a lesser extent, sulfur, phosphorus, selenium, and an occasional halogen."</ref> and [[Biology:Biogeochemical cycle|geochemical]] roles.<ref name="Cao 2021, pp. 20"/> While their physical and chemical character is "moderately non-metallic", on a net basis,<ref name="Cao 2021, pp. 20"/> all of them have corrosive aspects. Hydrogen can [[Chemistry:Anaerobic corrosion|corrode metals]]. Carbon corrosion can occur in [[Physics:Fuel cell|fuel cell]]s.<ref>Zhao, Tu & Chan 2021</ref> [[Earth:Acid rain|Acid rain]] is caused by dissolved nitrogen or sulfur. Oxygen corrodes iron via [[Chemistry:Rust|rust]]. White phosphorus, the most unstable form, ignites in air and produces [[Chemistry:Phosphoric acid|phosphoric acid]] residue.<ref>Kosanke et al. 2012, p. 841</ref> Untreated selenium in soils can give rise to corrosive [[Chemistry:Hydrogen selenide|hydrogen selenide]] gas.<ref>Wasewar 2021, pp. 322–323</ref> When combined with metals, the unclassified nonmetals can form high [[Physics:Hardness|hardness]] ([[Physics:Interstitial compound|interstitial]] or [[Chemistry:Refractory|refractory]]) compounds,<ref>Messler 2011, p. 10</ref> on account of their relatively small atomic radii and sufficiently low ionization energies.<ref name="Cao 2021, pp. 20"/> They show a tendency to [[Chemistry:Catenation|bond to themselves]], especially in solid compounds.<ref>King et al. 1994, p. 1344; Powell & Tims 1974, pp. 189–191; Cao et al. 2021, pp. 20–21</ref> [[Chemistry:Diagonal relationship|Diagonal periodic table relationships]] among these nonmetals echo similar relationships among the metalloids.<ref>Vernon 2020, pp. 221–223; Rayner-Canham 2020, p. 216</ref>

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.<ref>Atkins 2001, pp. 24–25</ref>

Unclassified nonmetals typically occur in elemental forms (oxygen, sulfur) or are found in association with either of these two elements:<ref name="occur">Cox 1997, pp. 130–132; Emsley 2011, passim</ref>

* Hydrogen occurs in the world's oceans as a component of water, and in [[Chemistry:Natural gas|natural gas]] as a component of [[Chemistry:Methane|methane]] and [[Chemistry:Hydrogen sulfide|hydrogen sulfide]].<ref>National Center for Biotechnology Information 2021</ref>
* Carbon occurs in limestone, dolomite, and marble, as carbonates.<ref>Emsley 2011, p. 113</ref> Less well known is carbon as graphite, which mainly occurs in [[Earth:Metamorphic rock|metamorphic]] silicate rocks,<ref>Greenwood & Earnshaw 2002, p. 270–271</ref> as a result of the compression and heating of sedimentary carbon compounds.<ref>Khan 2001, p. 59</ref>
* Oxygen is found in the atmosphere; in the oceans as a component of water; and in the crust as [[Chemistry:Oxide mineral|oxide mineral]]s.<ref>Emsley 2011, pp. 376, 380, 640</ref>
* Phosphorus minerals are widespread, usually as phosphorus-oxygen phosphates.<ref>Cox 1997, pp. 130; Emsley 2011, p. 393</ref>
* 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.<ref>Cox 1997, pp. 130; Emsley 2011, pp. 515–516, 518</ref>
* Selenium occurs in metal sulfide ores, where it partially replaces the sulfur; elemental selenium is occasionally found.<ref>Boyd 2011, p. 570</ref>

==Allotropes==
{{Main|Physics:Allotropy}}
[[Image:C60-Fulleren-kristallin.JPG|thumb|Brownish crystals of buckminsterfullerene (С<sub>60</sub>), a semiconducting allotrope of carbon|alt=a haphazard aggregate of brownish crystals]]

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.<ref>Barton 2021, p. 200</ref>

Among the halogen nonmetals, and unclassified nonmetals:
* Iodine is known in a semiconducting [[Physics:Amorphous|amorphous]] form.<ref>Shanabrook, Lannin & Hisatsune 1981, pp. 130‒133</ref>
* Graphite, the standard state of carbon, is a fairly good electrical conductor. The [[Chemistry:Diamond|diamond]] allotrope of carbon is clearly nonmetallic, being translucent and an extremely poor electrical conductor.<ref>Borg & Dienes 1992, p. 26</ref> Carbon is known in several other allotropic forms, including semiconducting [[Chemistry:Buckminsterfullerene|buckminsterfullerene]],<ref>Wiberg 2001, p. 796</ref> and [[Physics:Amorphous|amorphous]]<ref>Shang et al. 2021</ref> and [[Physics:Paracrystallinity|paracrystalline]] (mixed amorphous and crystalline)<ref>Tang et al. 2021</ref> varieties.
* Nitrogen can form gaseous [[Chemistry:Tetranitrogen|tetranitrogen]] (N<sub>4</sub>), an unstable polyatomic molecule with a lifetime of about one microsecond.<ref>Cacace, de Petris & Troiani 2002, pp. 480‒481</ref>
* Oxygen is a diatomic molecule in its standard state; it also exists as [[Chemistry:Ozone|ozone]] (O<sub>3</sub>), an unstable nonmetallic allotrope with an "indoors" [[Physics:Half-life|half-life]] of around half an hour, compared to about three days in ambient air at 20&nbsp;°C.<ref>Koziel 2002, p. 18</ref>
* Phosphorus, uniquely, exists in several allotropic forms that are more stable than its standard state as white phosphorus (P<sub>4</sub>). The white, red, and black allotropes are probably the best known; the first is an insulator; the latter two are semiconductors.<ref>Gusmão, Sofer & Pumera 2017, p. 8052–8053; Berger 1997, p. 84; Vernon 2013, pp. 1704‒1705</ref> Phosphorus also exists as [[Chemistry:Diphosphorus|diphosphorus]] (P<sub>2</sub>), an unstable diatomic allotrope.<ref>Piro et al. 2006, pp. 1276‒1279</ref>
* Sulfur has more allotropes than any other element.<ref>Steudel & Eckert 2003, p. 1</ref> [[Chemistry:Sulfur#Allotropes|Amorphous sulfur]], a metastable mixture of such allotropes, is noted for its elasticity.<ref>Greenwood & Earnshaw 2002, pp. 659–660</ref>
* Selenium has several nonmetallic allotropes, all of which are much less electrically conducting than its standard state of gray "metallic" selenium.<ref>Moss 1952, p. 192; Greenwood & Earnshaw 2002, p. 751</ref>

All the elements most commonly recognized as metalloids form allotropes:
* Boron is known in [[Chemistry:Allotropes of boron|several crystalline and amorphous forms]].<ref>Donohue 1982, pp. 48–81</ref>
* Silicon can form crystalline (diamond-like); amorphous; and [[Physics:Orthorhombic crystal system|orthorhombic]] Si<sub>24</sub> allotropes.<ref>Shiell at al. 2021</ref>
* At a pressure of about 10–11&nbsp;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.<ref>Zhao et al. 2017</ref>
* Arsenic and antimony form several well-known allotropes (yellow, grey, and black).<ref>Donohue 1982, pp. 302–310</ref>
* Tellurium is known in crystalline and amorphous forms.<ref>Brodsky et al. 1972, p. 609–614</ref>

Other allotropic forms of nonmetallic elements are known, either under pressure or in [[Physics:Monolayer|monolayer]]s. Under sufficiently high pressures, at least half of the nonmetallic elements that are semiconductors or insulators,{{#tag:ref|B; Si, Ge; N, P; O, S, Se, Te; halogen nonmetals; and the noble gases.<ref name="K&W"/>|group=n}} starting with phosphorus at 1.7&nbsp;GPa, have been observed to form metallic allotropes.<ref>Yousuf 1998, p. 425; Elatresh & Bonev 2020</ref>{{#tag:ref|In 2020, high-pressure studies and experiments were said to represent "a very active and vigorous research field".<ref>Errandonea 2020, p. 595</ref>|group=n}} Single layer two-dimensional forms of nonmetals include [[Chemistry:Borophene|borophene]] (boron), [[Physics:Graphene|graphene]] (carbon), [[Chemistry:Silicene|silicene]] (silicon), [[Physics:Phosphorene|phosphorene]] (phosphorus), [[Chemistry:Germanene|germanene]] (germanium), arsenene (arsenic), antimonene (antimony), and tellurene (tellurium), collectively referred to as ''[[Physics:Single-layer materials|xenes]]''.<ref>Su et al. 2020, pp. 1621–1649</ref>

==Prevalence and access==

===Abundance===
{| class="wikitable floatright" style="font-size: 95%"
|+ Approximate nonmetal composition<br>of the Earth and its biomass, by weight<ref>Nelson 1987, p. 732: crust, atmosphere, hydrosphere; Fortescue 2012, pp. 56, 65: biomass</ref>
|-
! Domain !! Main components !! Next most<br>abundant
|-
| 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.<ref>MacKay, MacKay & Henderson 2002, p. 200</ref> Oxygen is thought to be the next most abundant element, at about 0.1%.<ref>Cox 1997, pp. 17, 19</ref> 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 hypothesized to be made of [[Astronomy:Dark energy|dark energy]] and [[Astronomy:Dark matter|dark matter]], both of which are currently poorly understood.<ref>Ostriker & Steinhardt 2001, pp. 46‒53; Zhu 2020, p. 27</ref>

Five nonmetals—namely hydrogen, carbon, nitrogen, oxygen and silicon—constitute the bulk of the [[Earth:Earth's crust|Earth's crust]], atmosphere, [[Earth:Hydrosphere|hydrosphere]], and [[Earth:Biomass (ecology)|biomass]], in the quantities shown in the table.

===Extraction===
[[File:Polycrystalline-germanium.jpg|thumb|upright=0.6|right|Germanium occurs in some zinc-copper-lead ore bodies, in quantities sufficient to justify extraction.<ref>Höll et al. 2007</ref> In 2022, the 99.999% pure form was priced at US$1300 per kilogram.<ref>U.S. Geological Survey 2023, p. 78</ref>|alt=Greyish lustrous block with uneven cleaved surface.]]

Nonmetals, and metalloids, are extracted in their raw forms from:<ref name="Emsley">Emsley 2011, passim</ref>
* ''[[Earth:Brine|brine]]''—chlorine, bromine, iodine;
* ''liquid air''—nitrogen, oxygen, neon, argon, krypton, xenon;
* ''minerals''—boron ([[Chemistry:Borate mineral|borate mineral]]s); carbon (coal; diamond; graphite); fluorine (fluorite); silicon ([[Chemistry:Silica|silica]]); phosphorus (phosphates); antimony ([[Chemistry:Stibnite|stibnite]], [[Chemistry:Tetrahedrite|tetrahedrite]]); iodine (in [[Chemistry:Sodium iodate|sodium iodate]] and [[Chemistry:Sodium iodide|sodium iodide]]);
* ''natural gas''—hydrogen, helium, sulfur; and
* ''ores'', as processing byproducts—germanium ([[Chemistry:Zinc|zinc]] ores); arsenic ([[Chemistry:Copper|copper]] and [[Chemistry:Lead|lead]] ores); selenium, tellurium (copper ores); and radon (uranium-bearing ores).

===Cost===
Day to day costs will vary depending on purity, quantity,{{#tag:ref|For example, as at April 2023, the commercial price of silicon was $4 per pound or $0.0088 per gram.<ref>U.S. Geological Survey 2023, p. 153</ref> On the other hand, the price quoted for a 335 gram sample of silicon for hobbyists and science enthusiasts was about $57, or 0.170 per gram, or about 20 times the commercial price.<ref>Billing Metals & Manufacturing</ref>|group=n}} market conditions, and supplier surcharges.<ref>U.S. Geological Survey 2023, p. 72, 86, 147</ref>

Based on the available literature as of April 2023,<!-- The "available" literature means non-commercial RS that actually list prices of the elements in question --> the cited costs of most nonmetals are less than the $US0.74 per gram cost of silver.<ref>U.S. Geological Survey 2023, pp. 32, 34, 78, 82, 84, 91, 156, 158, 160, 170, 176;

Kopteva,Kalimullin & Tcvetkov 2021, p. 1;

Oztemel, Salt & Salt 2022, p. 5;

Neice & Zornow 2016, p. 1268;

Howe-Grant 1995, p. 17;

Dalakov, Neuber & Herzog R 2020;

Boysen, Cristóbal & Hilbig 2020, pp. 475–489;

Gardner & Menon 2018, p. 455;

Rajarathnam & Assallo 2016, p. 3;

Xia, Ning & Zhu 2020</ref> The exceptions are boron, phosphorus, germanium, xenon, and radon (notionally):

* Boron costs around $25 per gram for 99.7% pure polycrystalline chunks with a particle size of about 1&nbsp;cm.<ref>Chand, Kumar & Bhumla 2022, p. 22058</ref> Earlier, in 1997, boron was quoted at $280 per gram for polycrystalline 4-to-6-mm-diameter rods of 99.999% purity,<ref>Berger 1997, p. 42</ref> about 10 times the then $28.35 per gram cost of gold.<ref>U.S. Geological Survey 1998</ref>
* In 2020, phosphorus in its most-stable black form could "cost up to $1,000 per gram",<ref name=BSU>Boise State University 2020</ref> more than 15 times the cost of gold, whereas ordinary red phosphorus, in 2017, was priced at about $3.40 per kilogram.<ref>Hu, Shen & Yu 2017, p. 595</ref> Researchers hoped to be able to reduce the cost of black phosphorus to as low as $1 per gram.<ref name=BSU/>
* Germanium and xenon cost about $1.30 and $7.60 per gram.<ref>Gardner & Menon 2018, p. 454; U.S. Geological Survey 2023, p. 78</ref>
* Up to 2013, radon was available from the [[Organization:National Institute of Standards and Technology|National Institute of Standards and Technology]] for $1,636 per 0.2&nbsp;ml unit of issue, equivalent to about $86,000,000 per gram, with no indication of a discount for bulk quantities.<ref>National Institute of Standards and Technology 2013</ref>

==Uses==
The distinctive properties of nonmetallic elements allow for specific applications that often cannot be fulfilled by metallic elements alone. Living organisms are composed almost entirely of the nonmetals hydrogen, oxygen, carbon, and nitrogen. Nonmetallic elements are important to industries ranging from electronics and energy storage to agriculture and chemical production, for example:

* Carbon fibers possess high strength and low weight, making them ideal for applications in aerospace, [[Engineering:Sports equipment|sports equipment]], and {{wipe|Automotive industry}}. [[Physics:Graphene|Graphene]], a single layer of carbon atoms, has exceptional electrical and thermal conductivity, making it valuable for electronic devices, [[Engineering:Energy storage|energy storage]], and composite materialss.<ref>Emsley 2011, pp. 114–115</ref>
* Nitrogen is a key component in the production of [[Chemistry:Fertilizer|fertilizer]]s, which enhance crop growth and agricultural productivity. It's low temperature properties make it useful for [[Physics:Cryogenics|cryogenic]] applications, such as preserving biological samples and freezing food.<ref>Emsley 2011, pp. 363–364</ref>
* In life support, oxygen is vital for human [[Biology:Cellular respiration|respiration]], and it is used in medical settings to assist patients with respiratory difficulties. It supports [[Physics:Combustion|combustion]] and is used in various industrial processes, such as metal smelting and waste incineration.<ref>Emsley 2011, pp. 376–377; 379</ref>
* In [[Physics:Semiconductor|semiconductor]]s, silicon is the backbone of the electronics industry. It is used to manufacture computer chips, [[Physics:Solar cell|solar cell]]s, and various electronic components. [[Chemistry:Silicon dioxide|Silicon dioxide]] (silica) is used in the production of [[Chemistry:Glass|glass]], ceramics, and [[Engineering:Optical fiber|optical fiber]]s, enabling applications in windows, lenses, and communication networks.<ref>Emsley 2011, pp. 484–489</ref>
* Sulfur is used in the production of [[Chemistry:Sulfuric acid|sulfuric acid]], one of the most widely used industrial chemicals. It is also used in the synthesis of various organic compounds. Sulfur compounds are crucial in the [[Chemistry:Vulcanization|vulcanization]] process, which imparts strength and elasticity to [[Chemistry:Rubber|rubber]] products.<ref>Emsley 2011, pp. 511, 516–517</ref>

Shared uses of different subsets of the nonmetals encompass their presence in, or specific uses in the fields of air replacements (inert); dyestuffs; flame retardants or extinguishers; household accoutrements; [[Physics:Laser|laser]]s and lighting; mineral acids; [[Engineering:Plug-in hybrid|plug-in hybrid]] vehicles; and [[Chemistry:Shielding gas|welding gases]].<ref name="Emsley"/><ref>Bhuwalka et al. 2021, pp.&nbsp;10097–10107</ref> To the extent that metalloids show metallic character, they have speciality uses extending to (for example) oxide glasses and [[Chemistry:Alloy|alloy]]ing components.<ref>Gaffney & Marley 2017, p. 27</ref>

==History, background, and taxonomy==

===Discovery===
{{main|Chemistry:Discovery of the nonmetals}}
[[File:Joseph Wright of Derby The Alchemist.jpg|thumb|upright=1.0|''The Alchemist Discovering Phosphorus'' (1771) by Joseph Wright. The alchemist is Hennig Brand; the glow emanates from the combustion of phosphorus inside the flask.|alt=a man kneels in one corner of a darkened room, before a glowing flask; some assistants are further behind him and discernible in the dark]]

Most nonmetals were discovered in the 18th and 19th centuries. Before then, carbon, sulfur, and antimony were known in [[History:Classical antiquity|antiquity]]; arsenic was discovered during the [[History:Middle Ages|Middle Ages]] (by [[Biography:Albertus Magnus|Albertus Magnus]]); and [[Biography:Hennig Brand|Hennig Brand]] isolated phosphorus from urine in 1669. Helium (1868) holds the distinction of being the only element not first discovered on Earth.{{#tag:ref|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{{nbsp}}... I did not know whether the substance{{nbsp}}... was a metal like [[Chemistry:Calcium|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".<ref>Labinger 2019, p. 305</ref>|group=n}} Radon is the most recently discovered nonmetal, being found only at the end of the 19th century.<ref name="Emsley"/>

Chemistry- or physics-based techniques used in the isolation efforts were [[Physics:Spectroscopy|spectroscopy]], [[Fractional distillation|fractional distillation]], radiation detection, [[Chemistry:Electrolysis|electrolysis]], ore acidification, displacement reactions, [[Physics:Combustion|combustion]], and heating; a few nonmetals occurred naturally as free elements:

*Of the noble gases, helium was detected via its yellow line in the [[Astronomy:Stellar corona|coronal spectrum]] of the sun, and later by observing the bubbles escaping from uranite UO<sub>2</sub> dissolved in acid. Neon through xenon were obtained via [[Fractional distillation|fractional distillation]] of air. Radon was first observed emanating from compounds of [[Chemistry:Thorium|thorium]], three years after [[Biography:Henri Becquerel|Henri Becquerel]]'s discovery of radiation in 1896.<ref>Emsley 2011, pp. 42–43, 219–220, 263–264, 341, 441–442, 596, 609</ref>
*The halogen nonmetals were obtained from their [[Chemistry:Halide|halide]]s via either [[Chemistry:Electrolysis|electrolysis]], adding an acid, or displacement. Some chemists died as a result of their experiments trying to isolate fluorine.<ref>Emsley 2011, pp. 84, 128, 180–181, 247</ref>
*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 [[Chemistry:Mercury(I) oxide|mercurous oxide]]; phosphorus was liberated by heating [[Chemistry:Microcosmic salt|ammonium sodium hydrogen phosphate]] (Na(NH<sub>4</sub>)HPO<sub>4</sub>), as found in [[Biology:Urine|urine]];<ref>Cook 1923, p. 124</ref> sulfur occurred naturally as a free element; and selenium{{#tag:ref|Berzelius, who discovered selenium, thought it had the properties of a metal, combined with the properties of sulfur.<ref>Weeks 1945, p. 161</ref>|group=n}} was detected as a residue in [[Chemistry:Sulfuric acid|sulfuric acid]].<ref>Emsley 2011, pp. 113, 363, 378, 477, 514–515</ref>
*Most of the elements commonly recognized as metalloids were isolated by heating their oxides ([[Chemistry:Borax|boron]], silicon, [[Chemistry:Arsenic trioxide|arsenic]], tellurium) or a sulfide ([[Chemistry:Germanium disulfide|germanium]]).<ref name="Emsley"/> Antimony was known in its native form, as well as being attainable by heating its sulfide.<ref>Weeks 1945, p. 22; Emsley 2011, p. 40</ref>

===Origin of the concept===
The distinction between [[Chemistry:Metal|metal]]s and nonmetals arose, in a convoluted manner, from a crude recognition of [[Philosophy:Natural kind|different kinds]] of matter, namely pure substances, mixtures, compounds and elements. Thus, matter could be divided into pure substances (such as salt, [[Chemistry:Sodium bicarbonate|bicarb of soda]], or sulfur) and mixtures ([[Chemistry:Aqua regia|aqua regia]], [[Chemistry:Gunpowder|gunpowder]], or [[Chemistry:Bronze|bronze]], for example); and pure substances eventually could be distinguished as compounds and elements.<ref>Klein 1994, p. 168</ref> "Metallic" elements then seemed to have broadly distinguishable attributes that other elements did not, such as their ability to conduct heat or for their "[[Chemistry:Earth (historical chemistry)|earths]]" (oxides) to form basic solutions in water, for example as occurred with quicklime (CaO).<ref>Lidin 1996, pp. 64‒65</ref>

===Use of the term===
The term ''nonmetallic'' dates from as far back as 1566. In a medical treatise published that year, Loys de L’Aunay (a French doctor) described the different properties of plant substances from metallic and "non-metallic" land.<ref>de L'Aunay 1566, p. 7</ref>

In [[Chemistry:History of chemistry#17th and 18th centuries: Early chemistry|early chemistry]], Wilhelm Homberg (a German natural philosopher) referred to "non-metallic" sulfur in ''Des Essais de Chimie'' (1708).<ref>Homberg 1708, p. 350; vide Kim 2000</ref> He questioned the five-fold division of all matter into sulfur, mercury, salt, water, and earth, as postulated by {{interlanguage link|Étienne de Clave|fr}} (1641) in the ''New Philosophical Light of True Principles and Elements of Nature''.<ref>de Clave 1641</ref> Homberg's approach represented "an important move toward the modern concept of an element".<ref>Schlager & Lauer 2000, p. 370</ref>

Lavoisier, in his "revolutionary"<ref>Strathern 2000, p. 239</ref> 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).<ref>Criswell p. 1140</ref> In its first seventeen years, Lavoisier's work was republished in twenty-three editions in six languages, and "carried&nbsp;... [his] new chemistry all over Europe and America."<ref>Salzberg 1991, p. 204</ref>

===Suggested distinguishing criteria===
{|class="wikitable floatright" style="line-height: 1.3; font-size: 95%; margin-top:1.2em; margin-left:20px"
|+Some single properties used to distinguish between<br>metals and nonmetals listed by type and date of source
| {{indented plainlist|indent=0.9em|
'''[[Physics:Physical property|Physical]]'''
* ◇[[Chemistry:Fusibility|Fusibility]], malleability<br />and [[Physics:Ductility|ductility]]<ref>Kendall 1811, pp. 298–303</ref>
* ◇[[Physics:Opacity (optics)|Opacity]]<ref>Brande 1821, p. 5</ref> 
* ◇Goldhammer-Herzfeld<br />criterion for metallization<ref>Edwards & Sienko 1983, pp. 691–96</ref>{{#tag:ref|The Goldhammer-Herzfeld ratio is roughly equal to the cube of the atomic radius divided by the [[Physics:Molar volume|molar volume]].<ref>Edwards & Sienko 1983, p. 693</ref> More specifically, it is the ratio of the force holding an individual atom's [[Physics:Valence electron|outer electron]]s 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.<ref>Herzfeld 1927; Edwards 2000, pp. 100–03</ref>|group=n}} 
* ◇Bulk [[Physics:Coordination number|coordination number]]<ref>Kubaschewski 1949, pp. 931–940</ref>
* ◇[[Physics:Electron excitation|Minimum excitation potential]]<ref>Remy 1956, p. 9</ref>
* ◇Sonorousness<ref>White 1962, p. 106: It makes a ringing sound when struck.</ref> 
* ◇[[Physics:State of matter|Physical state]]<ref name="Johnson1966">Johnson 1966, pp. 3–4</ref>
* ◇[[Physics:Critical temperature|Critical temperature]]<ref>Horvath 1973, pp. 335–336</ref>
  }}
| style="vertical-align:top"|{{indented plainlist|indent=0.9em| 
* ◇[[Physics:Enthalpy of vaporization|Enthalpy of vaporization]]<ref>Rao & Ganguly 1986</ref> 
* ◇Liquid range<ref>Smith & Dwyer 1991, p. 65: The difference between melting point and boiling point.</ref> 
* ◇Temperature coefficient<br /> of resistivity<ref name="Herman">Herman 1999, p. 702</ref>
* ◇Atomic conductance<ref name="Hill17">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 [[Physics:Molar volume|molar volume]].</ref> 
* ◇Packing efficiency<ref>Suresh & Koga 2001, pp. 5940–5944</ref>
* ◇3D electrical conductivity<ref>Johnson 2007, pp. 15–16</ref> 
* ◇[[Physics:Electrical conductivity|Electrical conductivity]]<br />at absolute zero<ref name="Edwards2010"/> 
* ◇[[Physics:Thermal conductivity|Thermal conductivity]]<ref>Povh & Rosin 2017, p. 131</ref>
  }}
| style="vertical-align:top"|{{indented plainlist|indent=0.9em|
'''Chemical'''
* ◇Cation formation<ref>Beach 1911</ref> 
* ◇Acid-base character of [[Chemistry:Oxide|oxide]]s<ref>Stott 1956, pp. 100–102</ref> 
* ◇[[Chemistry:Sulfate|Sulfate]] formation<ref name="ReferenceC">Abbott 1966, p. 18</ref> 
* ◇Oxide solubility in acids<ref>Parish 1977, p. 178</ref>
  }}
----
{{indented plainlist|indent=0.9em|
'''Electron related'''
* ◇[[Physics:Electron configuration|Configuration]]<ref>Sanderson 1957, p. 229</ref> 
* ◇[[Physics:Band structure|Structure]]<ref name="Edwards2010">Edwards 2010, pp. 941–965</ref>
  }}
|}

In 1809, [[Biography:Humphry Davy|Humphry Davy]]'s discovery of [[Chemistry:Sodium|sodium]] and [[Chemistry:Potassium|potassium]] "annihilated"<ref>Hare & Bache 1836, p. 310</ref> the line of demarcation between metals and nonmetals. Before then, metals had been distinguished on the basis of their ponderousness or relatively high densities.<ref>Chambers 1743: "That which distinguishes ''metals'' from all other bodies&nbsp;... is their heaviness&nbsp;..."</ref> Sodium and potassium, on the other hand, floated on water and yet were clearly metals on the basis of their chemical behaviour.<ref>Edwards 2000, p. 85</ref>

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, ordered by type and date of discovery.

Probably the most well-known property is that the electrical conductivity of a metal increases when temperature falls, whereas that of a nonmetal rises.<ref name="Herman"/> However, this does not follow for [[Chemistry:Plutonium|plutonium]], carbon, arsenic, and antimony. The electrical conductivity of plutonium is increased when this metal is heated within a temperature range of –175 to +125&nbsp;°C.<ref>Russell & Lee 2005, p. 466</ref> The electrical conductivity of carbon, despite being widely regarded as a nonmetal, is likewise increased when heated.<ref>Atkins et al. 2006, pp. 320–21</ref> Arsenic and antimony are sometimes classified as nonmetals, yet act similarly to carbon.<ref>Zhigal'skii & Jones 2003, p. 66</ref>

Kneen et al. suggested that the nonmetals could be distinguished 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."<ref name="Kneen218"/> Emsley noted that, "No single property{{nbsp}}... can be used to classify all the elements as either metals or nonmetals."<ref>Emsley 1971, p. 1</ref> Jones added that "classes are usually defined by more than two attributes".<ref>Jones 2010, p. 169</ref>

{|class="wikitable floatright" style="line-height: 1.3; font-size: 95%; margin-top:1.2em; margin-left:20px"
|+ The first 99 elements sorted by<br>density and electronegativity (EN){{#tag:ref|(a) The values are from Aylward and Findlay.<ref>Aylward & Findlay 2008, pp. 6–13; 126</ref><br>(b) Weighable amounts of the extremely radioactive elements [[Chemistry:Astatine|At (element 85)]], [[Chemistry:Francium|Fr (87)]], and elements with an atomic number higher than [[Chemistry:Einsteinium|Es (99)]], have not been prepared.<ref>Edelstein & Morrs 2009, p. 123</ref><br>(c) The density values used for At and Fr are theoretical estimates.<ref>Arblaster JW (ed.) 2018, p. 269; Lavrukhina & Pozdnyakov 1970, p. 269</ref>

<br>(d) Bjerrum classified "heavy metals" as those metals with densities above 7 g/cm<sup>3</sup>.<ref>Bjerrum N 1936</ref>

<br>(e) Vernon specified a minimum electronegativity of 1.9 for the metalloids, on the revised Pauling scale.<ref name="Vernon2013"/>|group=n}}
|-
| style="background:white; border-top:1px solid white; border-left:1px solid white;"|  ||colspan=2 style="text-align: center"|'''EN'''
|-
|style="vertical-align:top; column-width:2em"| '''Density''' ||style="vertical-align:top; column-width:12em"|  < 1.9  ||style="vertical-align:top; column-width:12em"| ≥ 1.9
|-
| < 7 gm/cm<sup>3</sup>|| Groups 1 and 2<br>Sc, Y, La<br>Ce, Pr, Eu, Yb<br>Ti, Zr, V; Al, Ga ||style="vertical-align:top"| Noble gases<br>F, Cl, Br, I<br>H, C, N, P, O, S, Se<br>''B, Si, Ge, As, Sb, Te''^
|-
| > 7 gm/cm<sup>3</sup>|| Nd, Pm, Sm, Gd, Tb, Dy<br>Ho, Er, Tm, Lu; Ac–Es;<br>Hf, Nb, Ta; Cr, Mn, Fe,<br>Co, Zn, Cd, In, Tl, Pb || style="vertical-align:top"|Ni, Mo, W, Tc, Re,<br>Platinum group metals,<br>[[Chemistry:Coinage metals|Coinage metals]], Hg; Sn,<br>Bi, Po, At
|-
|colspan=3|<span style="font-size:85%">^ italicized elements are commonly recognised by some authors as [[Chemistry:Metalloid|metalloid]]s</span>
|}

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 are hard and brittle or soft and crumbly, whereas metals are usually malleable and ductile; and nonmetal oxides are acidic.<ref>Johnson 1966, pp. 3–5, 15</ref>

According to Hein and Arena, nonmetals have relatively low densities and high electronegativity;<ref name="Hein"/> the accompanying table bears this out. Nonmetallic elements occupy the top left quadrant, where densities are relatively low and electronegativity values 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, by [[Philosophy:Ontology|rules of categorisation]], a nonmetal.<ref>Oderberg 2007, p. 97</ref>

===Development of subclasses===
A basic taxonomy of nonmetals was set out in 1844, by Alphonse Dupasquier, a French doctor, pharmacist and chemist.<ref>Bertomeu-Sánchez, Garcia-Belmar & Bensaude-Vincent 2002, pp. 248–249</ref> To facilitate the study of nonmetals, he wrote:<ref>Dupasquier 1844, pp. 66–67</ref>

:<span style="font-size:95%">They will be divided into four groups or sections, as in the following:</span>
::<span style="font-size:95%">Organogens O, N, H, C</span>
::<span style="font-size:95%">Sulphuroids S, Se, P</span>
::<span style="font-size:95%">Chloroides F, Cl, Br, I</span>
::<span style="font-size:95%">Boroids B, Si.</span>

An echo of Dupasquier's fourfold classification is seen in the modern subclasses. The organogens and sulphuroids represent the set of unclassified nonmetals. The chloroide nonmetals came to be independently referred to as ''halogens''.<ref>Berzelius 1832, pp. 248–276</ref> The boroid nonmetals were expanded into the ''metalloids'', starting from as early as 1864.<ref>''The Chemical News'' 1864, p. 22</ref> The noble gases, as a discrete grouping, were counted among the nonmetals from as early as 1900.<ref>Renouf 1901, pp. 268</ref>

===Comparison===
Some properties of metals, metalloids, unclassified nonmetals, halogen nonmetals, and noble gases are summarized in the following table.{{#tag:ref|See also [[Chemistry:Properties of metals, metalloids and nonmetals|Properties of metals, metalloids and nonmetals]], which treats metalloids as a class of their own.|group=n}} Physical properties apply to elements in their most stable forms under 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.<ref>Vernon 2020, pp. 217–225</ref>

{|class="wikitable" style="font-size:95%;"
|+Some cross-subclass properties
|- style="vertical-align:top"
! scope="col" style="width:10em;"|Physical property
! scope="col" style="width:20em" | Metals {{hr}} {{nobold|[[Chemistry:Alkali metal|alkali]], alkaline earth, [[Chemistry:Lanthanide|lanthanide]], [[Chemistry:Actinide|actinide]], [[Chemistry:Transition metal|transition]], [[Chemistry:Post-transition metal|post-transition]]}}
! scope="col" style="width:20em; border-right:2px dashed #CDCDCD; border-left:2px dashed #CDCDCD; border-top:2px dashed #CDCDCD"| Metalloids  {{hr}} {{nobold|[[Chemistry:Boron|boron]], [[Chemistry:Silicon|silicon]], [[Chemistry:Germanium|germanium]], [[Chemistry:Arsenic|arsenic]], [[Chemistry:Antimony|antimony]], [[Chemistry:Tellurium|tellurium]]}}
! scope="col" style="width:20em;" | Unclassified nonmetals {{hr}} {{nobold|[[Chemistry:Hydrogen|hydrogen]], [[Chemistry:Carbon|carbon]], [[Chemistry:Nitrogen|nitrogen]], [[Chemistry:Phosphorus|phosphorus]], [[Chemistry:Oxygen|oxygen]], [[Chemistry:Sulfur|sulfur]], [[Chemistry:Selenium|selenium]]}}
! scope="col" style="width:20em;" | Halogen nonmetals {{hr}} {{nobold|[[Chemistry:Fluorine|fluorine]], [[Chemistry:Chlorine|chlorine]], [[Chemistry:Bromine|bromine]], [[Chemistry:Iodine|iodine]]}}
! scope="col" style="width:20em;" | Noble gases {{hr}} {{nobold|[[Chemistry:Helium|helium]], [[Chemistry:Neon|neon]], [[Chemistry:Argon|argon]], [[Chemistry:Krypton|krypton]], [[Chemistry:Xenon|xenon]], [[Chemistry:Radon|radon]]}}
|- style="vertical-align:top"
| scope="row" |Form and heft<ref>Tregarthen 2003, p. 10</ref>
| style="border-right:2px dashed #CDCDCD"|{{indented plainlist|indent=0.9em|
* ◇ solid
* ◇ often [[Chemistry:Heavy metals|high density]] such as Fe, Pb, W
* ◇ some light metals including Be, Mg, Al
  }}
| style="border-right:2px dashed #CDCDCD"|{{indented plainlist|indent=0.9em|
* ◇ solid
* ◇ low to moderately high density
* ◇ all lighter than Fe
  }}
| {{indented plainlist|indent=0.9em|
* ◇ solid or gas
* ◇ low density
* ◇ H, N lighter than air<ref>Lewis 1993, pp. 28, 827</ref>
  }}
| {{indented plainlist|indent=0.9em|
* ◇ solid, liquid or gas
* ◇ low density
  }}
| {{indented plainlist|indent=0.9em|
* ◇ gas
* ◇ low density
* ◇ He, Ne lighter than air<ref>Lewis 1993, pp. 28, 813</ref>
  }}
|- style="vertical-align:top"
| scope="row" |Appearance
| lustrous<ref name="Kneen"/>
| style="border-right:2px dashed #CDCDCD; border-left:2px dashed #CDCDCD"|lustrous<ref name="Rochow 1966, p. 4">Rochow 1966, p. 4</ref>
| {{indented plainlist|indent=0.9em|
* ◇ lustrous: C, P, Se<ref>Wiberg 2001, p. 780; Emsley 2011, p. 397; Rochow 1966, pp. 23, 84</ref>
* ◇ colorless: H, N, O<ref>Kneen, Rogers & Simpson 1972, pp. 321, 404, 436</ref>
* ◇ colored: S<ref>Kneen, Rogers & Simpson 1972, p. 439</ref>}}
| {{indented plainlist|indent=0.9em|
* ◇ colored: F, Cl, Br<ref>Kneen, Rogers & Simpson 1972, p. 465</ref>
* ◇ lustrous: I<ref name="Vernon2013"/>}}
|  colorless<ref>Kneen, Rogers & Simpson 1972, p. 308</ref> 
|- style="vertical-align:top"
| scope="row" | [[Physics:Elasticity|Elasticity]]
| mostly malleable and ductile<ref name="Kneen"/> (Hg is liquid)
| style="border-right:2px dashed #CDCDCD; border-left:2px dashed #CDCDCD"|brittle<ref name="Rochow 1966, p. 4">Rochow 1966, p. 4</ref>
| C, black P, S, Se brittle; all four have less stable non-brittle forms<ref>Wiberg 2001, pp. 505, 681, 781; Glinka 1958, p. 355</ref>{{#tag:ref|Carbon as [[Chemistry:Graphite#Expanded graphite|exfoliated (expanded) graphite]],<ref>Chung 1987, pp. 4190‒4198; Godfrin & Lauter 1995, pp. 216‒218</ref> and as [[Physics:Carbon nanotube|carbon nanotube]] wire;<ref name="Janas"/> phosphorus as white phosphorus (soft as wax, pliable and can be cut with a knife, at room temperature);<ref name="Holderness 1979, p. 255">Faraday 1853, p. 42; Holderness & Berry 1979, p. 255</ref> sulfur as plastic sulfur;<ref name="ReferenceE">Partington 1944, p. 405</ref> and selenium as selenium wires.<ref name="ReferenceF">Regnault 1853, p. 208</ref>|group=n}}
| iodine is brittle<ref>Wiberg 2001, p. 416</ref>
| not applicable
|- style="vertical-align:top"
| scope="row" |[[Physics:Electrical resistivity and conductivity|Electrical conductivity]]
| good{{#tag:ref|Metals have electrical conductivity values of from {{val|6.9|e=3|u=S•cm<sup>−1</sup>}} for [[Chemistry:Manganese|manganese]] to {{val|6.3|e=5}} for [[Chemistry:Silver|silver]].<ref>Desai, James & Ho 1984, p. 1160; Matula 1979, p. 1260</ref>|group=n}}
| style="border-right:2px dashed #CDCDCD; border-left:2px dashed #CDCDCD"|{{indented plainlist|indent=0.9em|
* ◇ moderate: B, Si, Ge, Te
* ◇ good: As, Sb{{#tag:ref|Metalloids have electrical conductivity values of from {{val|1.5|e=-6|u=S•cm<sup>−1</sup>}} for boron to {{val|3.9|e=4}} for [[Chemistry:Arsenic|arsenic]].<ref>Schaefer 1968, p. 76; Carapella 1968, pp. 29‒32</ref>|group=n}}
  }}
| {{indented plainlist|indent=0.9em|
* ◇ poor: H, N, O, S
* ◇ moderate: P, Se
* ◇ good: C{{#tag:ref|Unclassified nonmetals have electrical conductivity values of from ca. {{val|1|e=−18|u=S•cm<sup>−1</sup>}} for the elemental gases to {{val|3|4}} in graphite.<ref name="Bog">Bogoroditskii & Pasynkov 1967, p. 77; Jenkins & Kawamura 1976, p. 88</ref>|group=n}}
  }}
| {{indented plainlist|indent=0.9em|
* ◇ poor: F, Cl, Br
* ◇ moderate: I{{#tag:ref|The halogen nonmetals have electrical conductivity values of from ca. {{val|1|e=-18|u=S•cm<sup>−1</sup>}} for F and Cl to {{val|1.7|e=-8|u=S•cm<sup>−1</sup>}} for iodine.<ref name="Bog"/><ref name="Greenwood 2002, p. 804">Greenwood & Earnshaw 2002, p. 804</ref>|group=n}}
  }}
| poor{{#tag:ref|The elemental gases have electrical conductivity values of ca. {{val|1|e=−18|u=S•cm<sup>−1</sup>}}.<ref name="Bog"/>|group=n}}
|- style="vertical-align:top"
| scope="row" |[[Physics:Electronic band structure|Electronic structure]]<ref name="K&W">Keeler & Wothers 2013, p. 293</ref>
| metallic (Bi is a semimetal)
| style="border-right:2px dashed #CDCDCD; border-left:2px dashed #CDCDCD"| semimetal (As, Sb) or semiconductor
| {{indented plainlist|indent=0.9em|
* ◇ semimetal: C
* ◇ semiconductor: P, Se
* ◇ insulator: H, N, O, S
  }}
| semiconductor (I) or insulator
| insulator
|- style="vertical-align:top"
! scope="col" style="width:10em;"|Chemical property
! scope="col" style="width:20em" | Metals {{hr}} {{nobold|[[Chemistry:Alkali metal|alkali]], alkaline earth, [[Chemistry:Lanthanide|lanthanide]], [[Chemistry:Actinide|actinide]], [[Chemistry:Transition metal|transition]], [[Chemistry:Post-transition metal|post-transition]]}}
! scope="col" style="width:20em; border-right:2px dashed #CDCDCD; border-left:2px dashed #CDCDCD; border-top:2px dashed #CDCDCD"| Metalloids  {{hr}} {{nobold|[[Chemistry:Boron|boron]], [[Chemistry:Silicon|silicon]], [[Chemistry:Germanium|germanium]], [[Chemistry:Arsenic|arsenic]], [[Chemistry:Antimony|antimony]], [[Chemistry:Tellurium|tellurium]]}}
! scope="col" style="width:20em;" | Unclassified nonmetals {{hr}} {{nobold|[[Chemistry:Hydrogen|hydrogen]], [[Chemistry:Carbon|carbon]], [[Chemistry:Nitrogen|nitrogen]], [[Chemistry:Phosphorus|phosphorus]], [[Chemistry:Oxygen|oxygen]], [[Chemistry:Sulfur|sulfur]], [[Chemistry:Selenium|selenium]]}}
! scope="col" style="width:20em;" | Halogen nonmetals {{hr}} {{nobold|[[Chemistry:Fluorine|fluorine]], [[Chemistry:Chlorine|chlorine]], [[Chemistry:Bromine|bromine]], [[Chemistry:Iodine|iodine]]}}
! scope="col" style="width:20em;" | Noble gases {{hr}} {{nobold|[[Chemistry:Helium|helium]], [[Chemistry:Neon|neon]], [[Chemistry:Argon|argon]], [[Chemistry:Krypton|krypton]], [[Chemistry:Xenon|xenon]], [[Chemistry:Radon|radon]]}}
|- style="vertical-align:top"
| scope="row" |General chemical behavior
| {{indented plainlist|indent=0.9em|
* ◇ strong to weakly metallic<ref>Kneen, Rogers & Simpson 1972, p. 264</ref>
* ◇ [[Chemistry:Noble metal|noble metal]]s are disinclined to react<ref>Rayner-Canham 2018, p. 203</ref>
  }}
| style="border-right:2px dashed #CDCDCD; border-left:2px dashed #CDCDCD|weakly nonmetallic{{#tag:ref|They always give "compounds less acidic in character than the corresponding compounds of the [typical] nonmetals".<ref name="Rochow 1966, p. 4">Rochow 1966, p. 4</ref>|group=n}}
| moderately nonmetallic<ref>Welcher 2001, p. 3–32: "The elements change from{{nbsp}}... metalloids, to moderately active nonmetals, to very active nonmetals, and to a noble gas."</ref>
| strongly nonmetallic<ref>Mackin 2014, p. 80</ref>
| {{indented plainlist|indent=0.9em|
* ◇ inert to nonmetallic<ref>Johnson 1966, pp. 105–108</ref>
* ◇ Rn shows some cationic behavior<ref>Stein 1969, pp. 5396‒5397; Pitzer 1975, pp. 760‒761</ref>
  }}
|- style="vertical-align:top"
| scope="row" |[[Chemistry:Oxide|Oxide]]s
|{{indented plainlist|indent=0.9em|
* ◇ basic; some amphoteric or acidic<ref>Porterfield 1993, p. 336</ref>
* ◇ V; Mo, W; Al, In, Tl; Sn, Pb; Bi are glass formers<ref name="Rao 2002, p. 22">Rao 2002, p. 22</ref>
* ◇ ionic, polymeric, layer, chain, and molecular structures<ref>Wells 1984, p. 534</ref>
  }}
| style="border-right:2px dashed #CDCDCD; border-left:2px dashed #CDCDCD"|{{indented plainlist|indent=0.9em|
* ◇ amphoteric or weakly acidic<ref>Rochow 1966, p. 4; Atkins et al. 2006, pp. 8, 122–123</ref>{{#tag:ref|Arsenic trioxide reacts with sulfur trioxide, forming arsenic "sulfate" As<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>.<ref>Wiberg 2001, p. 750</ref>|group=n}}
* ◇ B, Si, Ge, As, Sb, Te are glass formers<ref>Sidorov 1960, pp. 599‒603</ref>
* ◇ polymeric in structure<ref name="Pudd">Puddephatt & Monaghan 1989, p. 59</ref>
  }}
|{{indented plainlist|indent=0.9em|
* ◇ acidic ({{chem|||NO|2}}, {{chem|||N|2||O|5}}, {{chem|||SO|3}}, {{chem|||SeO|3}} strongly so)<ref>Sanderson 1967, p. 172; Mingos 2019, p. 27</ref> or neutral (H<sub>2</sub>O, CO, NO, N<sub>2</sub>O){{#tag:ref|CO and N<sub>2</sub>O are "formally the anhydrides of [[Chemistry:Formic acid|formic]] and [[Chemistry:Hyponitrous acid|hyponitrous acid]], respectively: CO + H<sub>2</sub>O → H<sub>2</sub>CO<sub>2</sub> (HCOOH, formic acid); N<sub>2</sub>O + H<sub>2</sub>O → H<sub>2</sub>N<sub>2</sub>O<sub>2</sub> (hyponitrous acid)".<ref>House 2008, p. 441</ref>|group=n}}
* ◇ P, S, Se are glass formers;<ref name="Rao 2002, p. 22"/> [[Chemistry:Carbon dioxide|CO<sub>2</sub>]] forms a glass at 40&nbsp;GPa<ref>McMillan 2006, p. 823</ref>
* ◇ mostly molecular<ref name="Pudd"/>
* ◇ C, P, S, Se have at least one polymeric form
  }}
|{{indented plainlist|indent=0.9em|
* ◇ acidic; {{chem|||ClO|2}}, {{chem|||Cl|2||O|7}}, {{chem|||I|2||O|5}} strongly so<ref>Mingos 2019, p. 27; Sanderson 1967, p. 172</ref>
* ◇ no glass formers reported
* ◇ molecular<ref name="Pudd"/>
* ◇ iodine has at least one polymeric form, [[Chemistry:Iodine pentoxide|I<sub>2</sub>O<sub>5</sub>]]<ref>King 1995, p. 182</ref>
  }}
|{{indented plainlist|indent=0.9em|
* ◇ metastable XeO<sub>3</sub> is acidic;<ref>Wiberg 2001, p. 399</ref> stable XeO<sub>4</sub> strongly so<ref>Kläning & Appelman 1988, p. 3760</ref>
* ◇ no glass formers reported
* ◇ molecular<ref name="Pudd"/>
* ◇ [[Chemistry:Xenon dioxide|XeO<sub>2</sub>]] is polymeric<ref>Ritter 2011, p. 10</ref>
  }}
|- style="vertical-align:top"
| scope="row" |Compounds with metals
| alloys<ref name="Kneen"/> or intermetallic compounds<ref>Yamaguchi & Shirai 1996, p. 3</ref>
| style="border-right:2px dashed #CDCDCD; border-left:2px dashed #CDCDCD"|tend to form alloys or intermetallic compounds<ref>Vernon 2020, p. 223</ref>
| {{indented plainlist|indent=0.9em|
* ◇ salt-like to covalent: H†, C, N, P, S, Se<ref>Vernon 2020, p. 220</ref>
* ◇ mainly ionic: O<ref>Woodward et al. 1999, p. 134</ref>
  }}
| mainly ionic<ref name="Cotton"/>
| simple compounds in ambient conditions not known{{#tag:ref|[[Chemistry:Disodium helide|Disodium helide]] (Na<sub>2</sub>He) is a compound of helium and sodium that is stable at high pressures above 113&nbsp;GPa. Argon forms an alloy with nickel, at 140&nbsp;GPa and close to 1,500 K however at this pressure argon is no longer a noble gas.<ref>Dalton 2019</ref>|group=n}}
|- style="vertical-align:top"
| scope="row" |[[Physics:Ionization energy|Ionization energy]] (kJ mol<sup>−1</sup>)‡<br/><ref>Aylward & Findlay 2008, p. 132</ref>
| {{indented plainlist|indent=0.9em|
* ◇ low to high
* ◇ 376&nbsp;to&nbsp;1,007
* ◇ average 643
  }}
| style="border-right:2px dashed #CDCDCD; border-left:2px dashed #CDCDCD"|{{indented plainlist|indent=0.9em|
* ◇ moderate
* ◇ 762&nbsp;to&nbsp;947
* ◇ average 833
  }}
| {{indented plainlist|indent=0.9em|
* ◇ moderate to high
* ◇ 941&nbsp;to&nbsp;1,402
* ◇ average 1,152
  }}
| {{indented plainlist|indent=0.9em|
* ◇ high
* ◇ 1,008&nbsp;to&nbsp;1,681
* ◇ average 1,270
  }} 
| {{indented plainlist|indent=0.9em|
* ◇ high to very high
* ◇ 1,037&nbsp;to&nbsp;2,372
* ◇ average 1,589
  }}
|- style="vertical-align:top"
| scope="row" |[[Chemistry:Electronegativity|Electronegativity]] (Pauling){{#tag:ref|Values for the noble gases are from Rahm, Zeng and Hoffmann.<ref>Rahm, Zeng & Hoffmann 2019, p. 345</ref>|group=n}}‡ <br/><ref>Aylward & Findlay 2008, p. 126</ref>
| {{indented plainlist|indent=0.9em|
* ◇ low to high
* ◇ 0.7 to 2.54
* ◇ average 1.5
  }} 
|style="border-right:2px dashed #CDCDCD; border-left:2px dashed #CDCDCD; border-bottom:2px dashed #CDCDCD;"|{{indented plainlist|indent=0.9em|
* ◇ moderately high
* ◇ 1.9 to 2.18
* ◇ average 2.05
  }} 
| {{indented plainlist|indent=0.9em|
* ◇ moderately high to high
* ◇ 2.19 to 3.44
* ◇ average 2.65
  }} 
| {{indented plainlist|indent=0.9em|
* ◇ high
* ◇ 2.66 to 3.98
* ◇ average 3.19
  }} 
| {{indented plainlist|indent=0.9em|
* ◇ high (Rn) to very high
* ◇ ca. 2.43 to 4.7
* ◇ average 3.3
  }}
|-
| colspan=6|<span style="font-size: 90%">† Hydrogen can also form alloy-like hydrides</span><ref>Steudel 1977, p. 176</ref><br /><span style="font-size: 90%">‡ The labels ''low, moderate, high'', and ''very high'' are arbitrarily based on the value spans listed in the table</span>
|}

==See also==
* [[Astronomy:CHON|CHON]] (carbon, hydrogen, oxygen, nitrogen)
* [[Chemistry:List of nonmetal monographs|List of nonmetal monographs]]
* [[Physics:Metallization pressure|Metallization pressure]]
* [[Physics:Nonmetal (astrophysics)|Nonmetal (astrophysics)]]
* Nonmetal (physics)
* Period 1 elements (hydrogen, helium)
* [[Chemistry:Properties of nonmetals (and metalloids) by group|Properties of nonmetals (and metalloids) by group]]
{{-}}

==Notes==
{{Reflist|group=n|colwidth=45em}}

==References==
===Citations===
{{Reflist|20em}}

===Bibliography===

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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 (eds.), ''From atoms to polymers: isoelectronic analogies'', VCH, New York, {{ISBN|978-0-89573-711-3}}

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{{refbegin|colwidth=40em|small=yes}}
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* <span id="Atkins2010"></span>Atkins PA & Overton T 2010, ''Shriver & Atkins' Inorganic Chemistry'', 5th ed., Oxford University Press, Oxford, {{ISBN|978-0-19-923617-6}}
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{{refend}}

==External links==
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[[Category:Nonmetals| ]]
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{{Sourceattribution|Nonmetal (chemistry)|1}}