A periodic table extract always/usually considered nonmetalsmetalloids, sometimes considered nonmetalsstatus as nonmetal or metal unconfirmedAt: Restrepo et al. 2006, p. 411; Thornton & Burdette 2010, p. 86; Hermann, Hoffmann & Ashcroft 2013, pp. 11604‒1‒11604‒5; Ts: Og: Smits et al. 2020
In the context of the periodic table, a nonmetal is a chemical element that mostly lacks distinctive metallic properties. Physically, nonmetals range from colorless gases such as hydrogen to lustrous crystalline solids such as iodine. They are usually less dense than metals and are often poor conductors of heat and electricity. Chemically, they have moderate to very high electronegativity—a tendency to attract electrons in a chemical bond—and their oxides tend to be acidic.
Seventeen elements are widely recognized as nonmetals. Additionally, some or all of six borderline elements (metalloids) are sometimes counted as nonmetals.
The two lightest nonmetals, hydrogen and helium, together make up about 98% of the mass of ordinary matter in the observable universe. Five nonmetallic elements—hydrogen, carbon, nitrogen, oxygen, and silicon—make up the bulk of Earth’s atmosphere, oceans, biosphere, and crust. Metals, however, are thought to constitute slightly more than half of Earth’s total mass.
Chemical compounds and alloys involving multiple elements including nonmetals are widespread. Industrial uses of nonmetals as the dominant component include in electronics, combustion, lubrication and machining.
Most nonmetallic elements were identified in the 18th and 19th centuries. While a distinction between metals and other minerals had existed since antiquity, a classification of chemical elements as metallic or nonmetallic emerged only in the late 18th century. Since then about twenty properties have been suggested as criteria for distinguishing nonmetals from metals. In contemporary research usage it is common to use a distinction between metal and not-a-metal based upon the electronic structure of the solids; the elements carbon, arsenic and antimony are then semimetals, a subclass of metals. The rest of the nonmetallic elements are insulators, some of which such as silicon and germanium can readily accommodate dopants that change their electrical conductivity leading to semiconducting behavior.
Definition and applicable elements Unless otherwise noted, this article describes the stable form of an element at or near standard temperature and pressure (STP).
Nonmetallic chemical elements are often broadly defined as those that largely lack the characteristic properties of metals—namely lustre, malleability, good thermal and electrical conductivity (arising from their electronic band structure), and a general tendency to form basic oxides.Malone & Dolter 2010, pp. 110–111 There is no widely accepted precise definition based on the extent to which these metallic properties are lacking;Godovikov & Nenasheva 2020, p. 4; Morely & Muir 1892, p. 241 any list of nonmetals is therefore open to debate and revision.Larrañaga, Lewis & Lewis 2016, p. 988
Fourteen elements are almost always recognized as nonmetals:Steudel 2020, p. 43: Steudel's monograph is an updated translation of the fifth German edition of 2013, incorporating the literature up to Spring 2019.
Three more are commonly classed as nonmetals, but some sources list them as "metalloids",Vernon 2013 a term which refers to elements intermediate between metals and nonmetals:Vernon 2020, p. 220; Rochow 1966, p. 4
One or more of the six elements most commonly recognized as metalloids are sometimes instead counted as nonmetals:
About 15–20% of the 118 known elementsIUPAC Periodic Table of the Elements are thus classified as nonmetals.
General properties Physical
Nonmetals can be generally characterised by their variety in form and color, relatively low density and limited pliability, and generally low melting points and conductivity.
Nonmetals show considerable physical diversity, ranging from colourless gases to lustrous solids. Their physical states, densities, mechanical properties, phase-change temperatures, thermal and electrical conductivities, and electronic structures vary widely, largely because of differences in how their atoms or molecules are arranged and bonded. Compared with metals, however, they are generally less dense and, when solid, are brittle or crumbly rather than malleable or ductile.
Nonmetals vary greatly in appearance, being colorless, colored or shiny. For the colorless nonmetals (hydrogen, nitrogen, oxygen, and the noble gases), no absorption of light happens in the visible part of the spectrum, and all visible light is transmitted.Wibaut 1951, p. 33: "Many substances ...are colourless and therefore show no selective absorption in the visible part of the spectrum." The colored nonmetals (sulfur, fluorine, chlorine, bromine) absorb some colors (wavelengths) and transmit the complementary or opposite colors. For example, chlorine's "familiar yellow-green colour ... is due to a broad region of absorption in the violet and blue regions of the spectrum".Elliot 1929, p. 629 The shininess of boron, graphite (carbon), silicon, black phosphorus, germanium, arsenic, selenium, antimony, tellurium, and iodine is a result of the electrons reflecting incoming visible light.Wiberg 2001, p. 416; Wiberg is here referring to iodine.
About half of nonmetallic elements are gases at or near standard temperature and pressure; most of the rest are solids. Bromine, the only liquid, is usually topped by a layer of its reddish-brown fumes. The gaseous and liquid nonmetals have very low densities, melting and boiling points, and are poor conductors of heat and electricity.Kneen, Rogers & Simpson 1972, pp. 261–264 The solid nonmetals have low densities and low mechanical strength—being either hard and brittle or soft and crumblyJohnson 1966, p. 4—and show wide variations in their melting, boiling, or sublimation points and thermal and electrical conductivity.
This diversity stems from variability in crystallographic structures and bonding arrangements. Covalent nonmetals existing as discrete atoms like xenon, or as small molecules, such as oxygen, sulfur, and bromine, have low melting and boiling points; many are gases at room temperature, as they are held together by weak London dispersion forces acting between their atoms or molecules, although the molecules themselves have strong covalent bonds.Zumdahl & DeCoste 2010, pp. 455, 456, 469, A40; Earl & Wilford 2021, p. 3-24 In contrast, nonmetals that form extended structures, such as long chains of selenium atoms,Shan et al. 2026, pp. 1635, 1634: Trigonal selenium has an average chain length of about 800 atoms, while individual measured chains extend to roughly 2,400 atoms or more. sheets of carbon atoms in graphite,Wiberg 2001, pp. 780 or three-dimensional lattices of silicon atomsWiberg 2001, pp. 824, 785 have higher melting and boiling points, and are all solids. Nonmetals closer to the left or bottom of the periodic table (and so closer to the metals) often have metallic interactions between their molecules, chains, or layers; this occurs in carbon,Charlier, Gonze & Michenaud 1994 phosphorus,Taniguchi et al. 1984, p. 867: "... black phosphorus ... [is] characterized by the wide valence bands with rather delocalized nature."; Carmalt & Norman 1998, p. 7: "Phosphorus ... should therefore be expected to have some metalloid properties."; Du et al. 2010: Interlayer interactions in black phosphorus, which are attributed to van der Waals-Keesom forces, are thought to contribute to the smaller band gap of the bulk material (calculated 0.19 eV; observed 0.3 eV) as opposed to the larger band gap of a single layer (calculated ~0.75 eV). arsenic,Wiberg 2001, pp. 742 selenium,Evans 1966, pp. 124–25 antimony,Wiberg 2001, pp. 758 telluriumStuke 1974, p. 178; Donohue 1982, pp. 386–87; Cotton et al. 1999, p. 501 and iodine.Steudel 2020, p. 601: "... Considerable orbital overlap can be expected. Apparently, intermolecular multicenter bonds exist in crystalline iodine that extend throughout the layer and lead to the delocalization of electrons akin to that in metals. This explains certain physical properties of iodine: the dark color, the luster and a weak electric conductivity, which is 3400 times stronger within the layers then perpendicular to them. Crystalline iodine is thus a two-dimensional semiconductor."; Segal 1989, p. 481: "Iodine exhibits some metallic properties ..." These interactions result in relatively good electrical conductivity in the case of carbon, arsenic and antimony; a smaller then expected band gap in phosphorus; smaller than expected distances between adjacent chains in selenium and tellurium; and contribute to weak electrical conductivity in iodine.
Covalently bonded nonmetals often share only the electrons required to achieve a noble gas electron configuration.DeKock & Gray 1989, pp. 423, 426—427 For example, nitrogen forms diatomic molecules featuring a triple bonds between each atom, both of which thereby attain the configuration of the noble gas neon. In contrast antimony has buckled layers in which each antimony atom is singly bonded with three other nearby atoms.Boreskov 2003, p. 45
Good electrical conductivity occurs when there is metallic bonding,Ashcroft and Mermin however the electrons in some nonmetals are not metallic. Good electrical and thermal conductivity associated with metallic electrons is seen in carbon (as graphite, along its planes), arsenic, and antimony. Good thermal conductivity occurs in boron, silicon, phosphorus, and germanium; such conductivity is transmitted though vibrations of the crystalline lattices (phonons) of these elements.Yang 2004, p. 9 Moderate electrical conductivity is observed in the semiconductorsWiberg 2001, pp. 416, 574, 681, 824, 895, 930; Siekierski & Burgess 2002, p. 129 boron, silicon, phosphorus, germanium, selenium, tellurium, and iodine.
Many of the nonmetallic elements are hard and brittle, where dislocations cannot readily move so they tend to undergo brittle fracture rather than deforming. Some do deform such as white phosphorus (soft as wax, pliable and can be cut with a knife at room temperature),Faraday 1853, p. 42; Holderness & Berry 1979, p. 255 plastic sulfur,Partington 1944, p. 405 and selenium which can be drawn into wires from its molten state.Regnault 1853, p. 208 Graphite is a standard solid lubricant where dislocations move very easily in the basal planes.
Chemical Nonmetals can be characterised in terms of their reactivity, quantitative properties such as electronegativity, and the nature of their compounds. Reactivity They range in reactivity from inert or barely reactive, through relatively unreactive and moderately reactive, to highly reactive. Examples include helium (inert); xenon (barely reactive); molecular nitrogen and graphite (relatively unreactive); sulfur and black phosphorus (moderately reactive); and fluorine (highly reactive)
In chemical reactions they tend to gain or share enough electrons to attain a noble-gas-like valence-shell electron configuration. This behavior is related to the relative stability of the filled valence shells in the noble gases. It is empirically represented by the duet and octet rules of thumb (noting several exceptions) and treated more fully by valence bond theory.Smith 1990, pp. 177–189
The noble gases are a special case in relation to this electron-counting pattern, since their valence shells are already filled and their atoms are correspondingly resistant to chemical reaction. This stability is not, however, absolute: the heavier noble gases, especially xenon, form a relatively small number of compounds, mostly with fluorine or oxygen, in which electron density is drawn away from the noble-gas atom and it is formally oxidised