BREAKING NEWS
Nonmetal

## Summary

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Extract (above) of periodic table (below) showing how often each element is classed nonmetalic:
14  effectively always[1]
3  frequently
[2]
(gray letters and boxes: metals)

Hydrogen is usually in group 1 (as in this full table) but can be in group 17 (as in the extract).[n 1]

In chemistry, nonmetals are a class of chemical elements whose chemical and physical properties contrast with those of metals. Most nonmetals gain electrons when reacting with a metal, form an acid if combined with oxygen and hydrogen, and are poor conductors of heat and electricity.[n 2] Nonmetals display more variety in color and state than do metals. About half are colored or colorless gases whereas nearly all metals are silvery-gray solids. Unlike most metals, they tend to have no structural uses.[6]

While the term dates from at least 1708, it has no widely-agreed precise definition.[7] Consequently, which elements are recognised as nonmetals depends on the classification criteria used by each author. Fourteen elements are effectively always included. Up to about nine more elements are frequently to sometimes added.[8]

Two nonmetals, hydrogen and helium, make up about 99% of ordinary (baryonic) matter in the observable universe by mass.[9] Three nonmetallic elements, hydrogen, oxygen and silicon, largely make up the Earth's crust, atmosphere, oceans and biosphere.[10][11] This is so even though the number of nonmetal elements is several times lower than the number of metal elements.

Most nonmetals have biological, technological or domestic roles or uses. Living organisms are composed almost entirely of the nonmetals hydrogen, oxygen, carbon, and nitrogen.[12] Near-universal uses for nonmetals are in medicine and pharmaceuticals;[13] lasers and lighting;[14] and household items.[15]

## Definition and applicable elements

There is no rigorous definition of a nonmetal.[16] Broadly, any element lacking a preponderance of metallic properties such as luster, deformability, and good electrical conductivity, can be regarded as a nonmetal.[17] Nevertheless some variation may be encountered among authors as to which elements are regarded as nonmetals, especially where the metals meet the nonmetals in periodic table terms.[18] This lack of consistency occurs due to the absence of a universally agreed criterion or set of criteria for distinguishing between metals and nonmetals. Classification decisions of individual authors then become subject to which property or properties they regard as being most indicative of metallic or nonmetallic character.[8]

The fourteen elements effectively always recognized as nonmetals are hydrogen, oxygen, nitrogen, and sulfur; the corrosive halogens fluorine, chlorine, bromine, and iodine; and the noble gases helium, neon, argon, krypton, xenon, and radon. Up to a further nine elements are sometimes or usually considered as nonmetals, including carbon, phosphorus, and selenium; and the elements otherwise commonly recognized as metalloids namely boron; silicon and germanium; arsenic and antimony; and tellurium, bringing the total up to twenty-three nonmetals.[4]

Astatine, the fifth halogen, is often ignored on account of its rarity and intense radioactivity;[19] the theoretical and experimental evidence is indirect, but strongly suggests that it is a metal. The superheavy elements copernicium (Z = 112) and oganesson (118) may turn out to be nonmetals; their actual status has not yet been confirmed.[20]

Since there are 118 known elements,[21] as of October 2021, the nonmetals are outnumbered by the metals several times.

## Concept origin, distinguishing criteria, and use of term

### Origin of the concept

The distinction between metals and nonmetals arose, in a convoluted manner, from a crude recognition of natural kinds of matter. Thus:

• matter could be divided into pure substances and mixtures;
• pure substances eventually could be distinguished as compounds and elements;
• "metallic" elements seemed to have broadly distinguishable attributes that other elements did not, such as their ability to conduct heat or for their "earths" (oxides) to form basic solutions in water, for example as occurred with quicklime (CaO).[29]

### Distinguishing criteria

 An example algorithmdistinguishing metals and nonmetals[30][31][32] 1. If an element is an electrical insulator or semiconductor it is a nonmetal 2. If it is soft and crumbly and forms an oxide with nitric acid it is a nonmetal (C, As, Sb) 3. All other elements, whether soft and crumbly (Ga, Bi);[n 3] ductile and malleable; hard and brittle; or liquid (Hg), are metals Although ontologically, anything not a metal is a "nonmetal", some authors divide the elements into metals, metalloids, and nonmetals.[33]

Many different properties have been used in attempts to refine the distinction between metals and nonmetals, including:

Johnson[39] noted that physical properties can best indicate the metallic or nonmetallic properties of an element, with the proviso that other properties will be needed in a number of ambiguous cases. Kneen et al.[8] added that:

It is merely necessary to establish and apply a criterion of metallicity…many arbitrary classifications are possible, most of which, if chosen reasonably, would be similar, but not necessarily identical…the relevance of the criterion can only be judged by the usefulness of the related classification.

Once a basis for distinguishing between the "two great classes of elements"[55] is established, the nonmetals are found to be those lacking the properties of metals,[56] to greater or lesser degrees.[57]

### Use of the term

The term "nonmetallic" dates from as far back as 1708 when Wilhelm Homberg mentioned "non-metallic sulfur" in his Des Essais de Chimie.[58] He had refuted the five-fold division of matter into sulfur, mercury, salt, water and earth, previously in vogue, as postulated by Étienne de Clave [fr] (1641) in New Philosophical Light of True Principles and Elements of Nature. Homberg's approach represented "an important move toward the modern concept of an element".[59] Subsequently, the first modern list of chemical elements was given by Lavoisier in his "revolutionary"[60] 1789 work Traité élémentaire de chimie in which he distinguished between simple metallic and nonmetallic substances. In its first seventeen years, Lavoisier's work was republished in twenty-three editions and six languages, and carried his "new chemistry" across Europe and America.[61]

## General properties

### Physical

Metals tend to have closer-packed structures. Nonmetals are more open-packed. Values for nonmetals that are normally gases are for the liquid state at boiling point.[n 4]

Physically, nonmetals in their most stable forms exist as either polyatomic solids (carbon, for example) with open-packed crystalline structures; diatomic molecules such as hydrogen (a gas) and bromine (a liquid); or monatomic gases (such as neon). They usually have small atomic radii. Metals, in contrast, are nearly all solid and close-packed, and mostly have larger atomic radii.[64] Solid nonmetals are brittle, as opposed to metals, which are generally ductile or malleable. Nonmetals usually have lower densities than metals; are mostly poorer conductors of heat and electricity; and tend to have significantly lower melting points and boiling points.[65]

The physical differences between metals and nonmetals arise from internal and external atomic forces. Internally, an atom's nuclear charge acts to hold its valence electrons in place. Externally, the same electrons are subject to attractive forces from the nuclear charges in nearby atoms. When the external forces are greater than, or equal to, the internal force, valence electrons are expected to become itinerant (free to move between atoms) and metallic properties are predicted. Otherwise nonmetallic properties are anticipated.[66]

### Chemical

Chemically, nonmetals mostly have higher ionization energies, higher electron affinities, higher electronegativity values, and higher standard reduction potentials than metals. Here, and in general, the higher these values, the more nonmetallic is the element in question.[67]

In chemical reactions, nonmetals tend to gain or share electrons unlike metals which tend to donate electrons. More specifically, and given the stability of the electron configurations of the noble gases (filled valence shells), nonmetals generally gain a number of electrons sufficient 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 encapsulated by the duet and octet rules of thumb (and for metals there is a less rigorously followed 18-electron rule). A key attribute of nonmetals is that they never form basic oxides; their oxides are generally acidic.[68] Moreover, solid nonmetals (including metalloids) react with nitric acid to form an oxide (carbon, silicon, sulfur, antimony, and tellurium) or an acid (boron, phosphorus, germanium, selenium, arsenic, iodine).[32]

Some typical chemistry-based
differences between metals and nonmetals[69]
Aspect Metals Nonmetals
Chemical
bonding
Seldom form
covalent bonds
Frequently form
covalent bonds
Metallic bonds (alloys)
between metals
Covalent bonds
between nonmetals
Ionic bonds between nonmetals and metals
Oxidation
states
Positive Negative or positive
Oxides Basic in lower oxides;
increasingly acidic
in higher oxides
Acidic
In aqueous
solution
[70]
Exist as anions
or oxyanions
Exist as cations

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 valence electrons. From left to right across each period of the periodic table the nuclear charge increases as the number of protons in the core increases.[71] There is an associated reduction in atomic radius[72] as the increasing nuclear charge draws the valence electrons closer to the core.[73] In metals, the effect of the nuclear charge is generally weaker than for nonmetallic elements. In chemical bonding, metals therefore tend to lose electrons, and form positively charged or polarized atoms or ions whereas nonmetals tend to gain those same electrons due to their stronger nuclear charge, and form negatively charged ions or polarized atoms.[74]

The number of compounds formed by nonmetals is vast.[75] The first ten places in a "top 20" table of elements most frequently encountered in 895,501,834 compounds, as listed in the Chemical Abstracts Service register for November 2nd, 2021, were occupied by nonmetals. Hydrogen, carbon, oxygen and nitrogen were 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.[76] Examples of nonmetal compounds are: boric acid (H
3
BO
3
), used in ceramic glazes; selenocysteine (C
3
H
7
NO
2
Se
), the 21st amino acid of life;[77] phosphorus sesquisulfide (P4S3), in strike anywhere matches; and teflon ((C
2
F
4
)n).[78]

### Complications

Complicating the chemistry of the nonmetals are the anomalies seen in the first row of each periodic table block, particularly in hydrogen, (boron), carbon, nitrogen, oxygen and fluorine; secondary periodicity or non-uniform periodic trends going down most of the p-block groups;[79] and unusual valence states in the heavier nonmetals. In this regard, Zuckerman and Nachod opined that:

The marvellous variety and infinite subtlety of the nonmetallic elements, their compounds, structures and reactions, is not sufficiently acknowledged in the current teaching of chemistry.[80]
Periodic table highlighting the first row of each block. 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) is not yet known.

First row anomaly. Starting with hydrogen, the first row anomaly largely arises from the electron configurations of the elements concerned. Hydrogen is noted for the different ways it forms bonds. It most commonly forms covalent bonds. It can lose its single valence electron in aqueous solution, leaving behind a bare proton with tremendous polarizing power.[81] This subsequently attaches itself to the lone electron pair of an oxygen atom in a water molecule, thereby forming the basis of acid-base chemistry.[82] A hydrogen atom in a molecule can form a second, weaker, bond with an atom or group of atoms in another molecule. Such bonding, "helps give snowflakes their hexagonal symmetry, binds DNA into a double helix; shapes the three-dimensional forms of proteins; and even raises water's boiling point high enough to make a decent cup of tea."[83]

Electronegativity values of the group 16 chalcogen elements showing a W-shaped alternation or secondary periodicity going down the group

For hydrogen and helium, and from boron to neon, since the 1s and 2p subshells have no inner analogues (i.e., there is no zeroth shell and no 1p subshell) and therefore experience no electron repulsion effects, they have relatively small radii, unlike the 3p, 4p and 5p subshells of heavier elements.[84] Ionization energies and electronegativities among these elements are consequently higher than would otherwise be expected, having regard to periodic trends. The small atomic radii of carbon, nitrogen, and oxygen facilitate the formation of double or triple bonds.[85]

Secondary periodicity. Immediately after the first row of the transition metals, the 3d electrons in the 4th row of elements, i.e., in gallium (a metal), germanium, arsenic, selenium, and bromine, are not as effective at shielding the increased nuclear charge. A similar effect accompanies the appearance of fourteen f-block metals between barium and lutetium, ultimately resulting in smaller than expected atomic radii for the elements from hafnium (Hf) onwards.[86] 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.[87]

Unusual valence 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 valences other than the lowest for their group (that is, 3, 2, 1, or 0) for example in phosphorus pentachloride (PCl5), sulfur hexafluoride (SF6), iodine heptafluoride (IF7), and xenon difluoride (XeF2).[88]

## Subclasses

Modern periodic table extract showing nonmetal subclasses.
moderately strong oxidising agent ‡ strong oxidising agent[n 5]

### Historical

A basic taxonomy of nonmetals was set out in 1844, by Alphonse Dupasquier, a French doctor, pharmacist and chemist.[99] To facilitate the study of nonmetals, he wrote:[100]

They will be divided into four groups or sections, as in the following:
Organogens O, N, H, C
Sulphuroids S, Se, P
Chloroides F, Cl, Br, I
Boroids B, Si.

Dupasquier's organogens and sulphuroids correspond to the set of unclassified nonmetals. Eventually thereafter:

• the chloroide nonmetals came to be independently referred to as halogens;[101]
• the boroid nonmetals came to expand into the metalloids, starting from as early as 1864;[102]
• varying configurations of the orgaonogen and the sulphuroid nonmetals have been referred to as, for example, basic nonmetals;[103] biogens;[104] central nonmetals;[105] CHNOPS;[106] essential elements;[107] "nonmetals";[108][n 6] orphan nonmetals;[109] or redox nonmetals;[110]
• the noble gases, as a discrete grouping, were counted among the nonmetals from as early as 1900.[111]

### Current

Approaches to classifying nonmetals may involve from as few as two subclasses to up to six or seven. For example, the Encyclopedia Britannica periodic table has noble gases, halogens, and other nonmetals, and splits the elements commonly recognized as metalloids between the "other metals" and the "other nonmetals";[112] the Royal Society of Chemistry periodic table uses a different color for each of its eight main groups, and nonmetals can be found in seven of these.[113]

From right to left in periodic table terms, three or four kinds of nonmetals are more or less commonly discerned. These are:

• the relatively inert noble gases;
• a set of chemically strong halogen elements—fluorine, chlorine, bromine and iodine—sometimes referred to as nonmetal halogens[114] (the term used here) or stable halogens;[115]
• a set of unclassified nonmetals, including elements such as hydrogen, carbon, nitrogen, and oxygen, with no widely recognized collective name; and
• the chemically weak nonmetallic metalloids,[116] sometimes considered to be nonmetals and sometimes not.[n 7]

Since the metalloids occupy frontier territory, where metals meet nonmetals, their treatment varies from author to author. Some consider them separate from both metals and the nonmetals; some regard them as nonmetals[118] or as a sub-class of nonmetals;[119] others count some of them as metals, for example arsenic and antimony, due to their similarities to heavy metals.[120][n 8] Metalloids are here treated as nonmetals in light of their chemical behavior, and for comparative purposes.

Aside from the metalloids, some boundary fuzziness and overlapping (as occurs with classification schemes generally) can be discerned among the other nonmetal subclasses. Carbon, phosphorus, selenium, iodine border the metalloids and show some metallic character, as does hydrogen. Among the noble gases, radon is the most metallic and begins to show some cationic behavior, which is unusual for a nonmetal.[122]

#### Noble gases

Six nonmetals are classified as noble gases: helium, neon, argon, krypton, xenon, and the radioactive radon. In conventional periodic tables they occupy the rightmost column. They are called noble gases in light of their characteristically very low chemical reactivity.[123]

They have very similar properties, all being colorless, odorless, and nonflammable. With their closed valence shells the noble gases have feeble interatomic forces of attraction resulting in very low melting and boiling points.[124] That is why they are all gases under standard conditions, even those with atomic masses larger than many normally solid elements.[125]

Chemically, the noble gases have relatively high ionization energies, nil or negative electron affinities, and relatively high electronegativities. Compounds of the noble gases number in the hundreds although the list continues to grow,[126] with most of these occurring via oxygen or fluorine combining with either krypton, xenon or radon.[127]

In periodic table terms, an analogy can be drawn between the noble gases and noble metals such as platinum and gold, with the latter being similarly reluctant to enter into chemical combination.[128] As a further example, xenon, in the +8 oxidation state, forms a pale yellow explosive oxide, XeO4, while osmium, another noble metal, forms a yellow strongly oxidizing oxide, OsO4; and there are parallels in the formulas of the oxyfluorides: XeO2F4 and OsO2F4, and XeO3F2 and OsO3F2.[129]

#### Nonmetal halogens

A conventional periodic table showing the positions of the alkali metals (A) and the nonmetal halogens (H).

While the nonmetal halogens are corrosive and markedly reactive elements, they can be found in such innocuous compounds as ordinary table salt (NaCl). Their remarkable chemical activity as nonmetals can be contrasted with the equally remarkable chemical activity of the alkali metals such as sodium and potassium, located at the far left of the periodic table.[130]

Physically, fluorine and chlorine are pale yellow and yellowish green gases; bromine is a reddish-brown liquid; and iodine is a metallic-looking (under white light)[131] solid. Electrically, the first three are insulators while iodine is a semiconductor (along its planes).[132]

Chemically, they have high ionization energies, electron affinities, and electronegativity values, and are mostly relatively strong oxidizing agents.[133] Manifestations of this status include their intrinsically corrosive nature.[134] All four exhibit a tendency to form predominately ionic compounds with metals[135] whereas the remaining nonmetals, bar oxygen, tend to form predominately covalent compounds with metals.[n 9] The reactive and strongly electronegative nature of the nonmetal halogens represents the epitome of nonmetallic character.[139]

In periodic table terms, the counterparts of the highly nonmetallic halogens, in group 17 are the highly reactive metals, such as sodium and potassium, in group 1. Curiously most of the alkali metals are known to form –1 anions (something that rarely occurs among nonmetals) as if in imitation of the nonmetal halogens.[140]

#### Unclassified nonmetals

After the nonmetallic elements are classified as either noble gases, halogens or metalloids (following), the remaining seven nonmetals are hydrogen, carbon, nitrogen, oxygen, phosphorus, sulfur and selenium. Three are colorless gases (H, N, O); three have a metal-like appearance (C, P, Se); and one is yellow (S). Electrically, graphitic carbon is a semimetal along its planes[141] and a semiconductor in a direction perpendicular to its planes;[142] phosphorus and selenium are semiconductors;[143] and hydrogen, nitrogen, oxygen, and sulfur are insulators.[n 10]

They are generally regarded as being too diverse to merit a collective examination,[145][146] and have been referred to as other nonmetals,[147] or more plainly as nonmetals, located between metalloids and halogens.[148] Consequently, their chemistry tends to be taught disparately, according to their four respective periodic table groups,[149] for example: hydrogen in group 1; the group 14 carbon nonmetals (carbon, and possibly silicon and germanium); the group 15 pnictogen nonmetals (nitrogen, phosphorus, and possibly arsenic and antimony); and the group 16 chalcogen nonmetals (oxygen, sulfur, selenium, and possibly tellurium). Other subdivisions are possible according to the individual preferences of authors.[n 11]

Hydrogen, in particular, behaves in some respects like a metal and in others like a nonmetal.[151] Like a metal it can (first) lose its single valence electron;[152] it can stand in for alkali metals in typical alkali metal structures;[153] and is capable of forming alloy-like hydrides, featuring metallic bonding, with some transition metals.[154] On the other hand, it is an insulating diatomic gas, like a typical nonmetal, and in chemical reactions more generally, it has a tendency to attain the electron configuration of helium.[155] It does this by way of forming a covalent or ionic bond[154] or, if it has lost its valence electron, attaching itself to a lone pair of electrons.[156]

Some or all of these nonmetals nevertheless have several shared properties. Their physical and chemical character is "moderately non-metallic", on a net basis.[146] Being less reactive than the halogens[157] most of them, except for phosphorus, can occur naturally in the environment.[158] They have prominent biological[159][160] and geochemical roles.[146] When combined with halogens, unclassified nonmetals form (polar) covalent bonds.[161] When combined with metals they can form hard (interstitial or refractory) compounds,[162] in light of their relatively small atomic radii and sufficiently low ionization energy values.[146] Unlike the halogens, unclassified nonmetals show a tendency to catenate, especially in solid-state compounds.[163][146] Diagonal relationships among these nonmetals echo similar relationships among the metalloids.[145][164]

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".[165]

#### Metalloids

The six elements more commonly recognized as metalloids are boron, silicon, germanium, arsenic, antimony, and tellurium, with each having a metallic appearance. On a standard periodic table, they occupy a diagonal area in the p-block extending from boron at the upper left to tellurium at lower right, along the dividing line between metals and nonmetals shown on some periodic tables.[131]

They are brittle and only fair conductors of electricity and heat. Boron, silicon, germanium and tellurium are semiconductors. Arsenic and antimony have the electronic band structures of semimetals although both have less stable semiconducting allotropes.[131]

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.[131]

Like hydrogen among the unclassified nonmetals, boron is chemically similar to metals in some respects.[166][n 12] It has fewer electrons than orbitals available for bonding. Analogies with transition metals occur in the formation of complexes,[168] and adducts (for example, BH3 + CO →BH3CO and, similarly, Fe(CO)4 + CO →Fe(CO)5),[n 13] as well as in the geometric and electronic structures of cluster species such as [B6H6]2− and [Ru6(CO)18]2−.[170]

To the left of the weakly nonmetallic metalloids, in periodic table terms, are found an indeterminate set of weakly metallic metals (such as tin, lead and bismuth)[171] sometimes referred to as post-transition metals.[172] Dingle explains the situation this way:[173]

…with 'no-doubt' metals on the far left of the table, and no-doubt non-metals on the far right…the gap between the two extremes is bridged first by the poor (post-transition) metals, and then by the metalloids – which, perhaps by the same token, might collectively be renamed the 'poor non-metals'.

### Comparison

Properties of metals and those of the (sub)classes of metalloids, unclassified nonmetals, nonmetal halogens, and noble gases are summarized in the table.[n 14] Physical properties apply to elements in their most stable forms in ambient conditions, and are listed in loose order of ease of determination. Chemical properties are listed from general to specific, and then to descriptive. 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.

Some cross-subclass properties
Physical property Metals Metalloids Unclassified nonmetals Nonmetal halogens Noble gases
Form[174] solid (Hg is liquid) solid
• ◇ solid: C, P, S, Se
• ◇ gaseous: H, N, O
• ◇ solid: I
• ◇ liquid: Br
• ◇ gaseous: F, Cl
gaseous
Appearance lustrous[65] lustrous[175]
• ◇ lustrous: C, P, Se[176]
• ◇ colorless: H, N, O[177]
• ◇ colored: S[178]
colorless[180]
Elasticity mostly malleable and ductile[65] (Hg is liquid) brittle[175]
• ◇ C, black P, S and Se are brittle[181]
• ◇ the same four have less stable non-brittle forms[n 15]
iodine is brittle[187] not applicable
Electrical conductivity high[n 16]
• ◇ moderate: B, Si, Ge, Te
• ◇ high: As, Sb[n 17]
• ◇ low: H, N, O, S
• ◇ moderate: P, Se
• ◇ high: C[n 18]
• ◇ low: F, Cl, Br
• ◇ moderate: I[n 19]
low[n 20]
Electronic structure[192] metallic (Bi is a semimetal) semimetal (As, Sb) or semiconductor
• ◇ semimetal: C
• ◇ semiconductor: P, Se
• ◇ insulator: H, N, O, S
semiconductor (I) or insulator insulator
Chemical property Metals Metalloids Unclassified nonmetals Nonmetal halogens Noble gases
General chemical behavior
weakly nonmetallic[n 21] moderately nonmetallic[196] strongly nonmetallic[197]
• ◇ inert to nonmetallic[198]
• ◇ Rn shows some cationic behavior[199]
Ionization energy (kJ mol−1)†
(data page)
• ◇ low to high
• ◇ 376 to 1,007
• ◇ average 643
• ◇ moderate
• ◇ 762 to 947
• ◇ average 833
• ◇ moderate to high
• ◇ 941 to 1,402
• ◇ average 1,152
• ◇ high
• ◇ 1,008 to 1,681
• ◇ average 1,270
• ◇ high to very high
• ◇ 1,037 to 2,372
• ◇ average 1,589
Electronegativity (Pauling scale)[n 22]
(data page)
• ◇ very low to moderate
• ◇ 0.79 to 2.54
• ◇ average 1.5
• ◇ low
• ◇ 1.9 to 2.18
• ◇ average 2.05
• ◇ moderate to high
• ◇ 2.19 to 3.44
• ◇ average 2.65
• ◇ high
• ◇ 2.66 to 3.98
• ◇ average 3.19
• ◇ low (Rn) to very high
• ◇ 2.2 to 5.2
• ◇ average 3.38
Compounds with metals alloys[65] or intermetallic compounds[201] tend to form alloys or intermetallic compounds[202]
• ◇ salt-like to covalent: H‡, C, N, P, S, Se[203]
• ◇ mainly ionic: O[204]
mainly ionic[135] simple compounds in ambient conditions not known[n 23]
Oxides
• ◇ ionic, polymeric, layer, chain, and molecular structures[206]
• ◇ V; Mo, W; Al, In, Tl; Sn, Pb; Bi are glass formers[207]
• ◇ basic; some amphoteric or acidic[208]
• ◇ mostly molecular[209]
• ◇ C, P, S, Se are known in at least one polymeric form
• ◇ P, S, Se are glass formers;[207] CO2 forms a glass at 40 GPa[213]
• ◇ acidic (NO
2
, N
2
O
5
, SO
3
, and SeO
3
strongly so)[214][215] or neutral (H2O, CO, NO, N2O)[n 25]
• ◇ molecular[209]
• ◇ iodine is known in at least one polymeric form, I2O5[217]
• ◇ no glass formers reported
• ◇ acidic; ClO
2
, Cl
2
O
7
, and I
2
O
5
strongly so[215][214]
• ◇ molecular[209]
• XeO2 is polymeric[218]
• ◇ no glass formers reported
• ◇ metastable XeO3 is acidic;[219] stable XeO4 strongly so[220]
† The labels low, moderate, high, and very high are arbitrarily based on the value spans listed in the table
‡ Hydrogen can also form alloy-like hydrides
[221]

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.[222]

## Allotropes

Most nonmetallic elements exist in allotropic forms. Carbon, for example, occurs as graphite and as diamond. Such allotropes may exhibit physical properties that are more metallic or less nonmetallic.[223]

Among the nonmetal halogens, and unclassified nonmetals:

• Iodine is known in a semiconducting amorphous form.[224]
• Graphite, the standard state of carbon, is a fairly good electrical conductor. The diamond allotrope of carbon is clearly nonmetallic, being translucent and, as an insulator, an extremely poor electrical conductor.[225] Carbon is further known in several other allotropic forms, including semiconducting buckminsterfullerene (C60).[226]
• Nitrogen can form gaseous tetranitrogen (N4), an unstable polyatomic molecule with a lifetime of about one microsecond.[227]
• Oxygen is a diatomic molecule in its standard state; it also exists as ozone (O3), an unstable nonmetallic allotrope with an "indoors" half-life of around half an hour, compared to about three days in ambient air at 20°C.[228]
• Phosphorus, uniquely, exists in several allotropic forms that are more stable than that of its standard state as white phosphorus (P4). The white, red and black allotropes are probably the best known; the first is an insulator; the latter two are semiconductors.[229] Phosphorus also exists as diphosphorus (P2), an unstable diatomic allotrope.[230]
• Sulfur has more allotropes than any other element.[231] Amorphous sulfur, a metastable mixture of such allotropes, is noted for its elasticity.[232]
• Selenium has several nonmetallic allotropes, all of which are much less electrically conducting than its standard state of gray "metallic" selenium.[233]

All the elements most commonly recognized as metalloids form allotropes. Boron is known in several crystalline and amorphous forms. The discovery of a quasi-spherical allotropic molecule, borospherene (B40), was announced in 2014. Silicon was most recently known only in its crystalline and amorphous forms. The synthesis of an orthorhombic allotrope, Si24, was subsequently reported in 2014.[234] At a pressure of ca. 10–11 GPa, germanium transforms to a metallic phase with the same tetragonal structure as tin; when decompressed—and depending on the speed of pressure release—metallic germanium forms a series of allotropes that are metastable in ambient conditions.[235] Arsenic and antimony form several well-known allotropes (yellow, grey, and black). Tellurium is known in its crystalline and amorphous forms.[236]

Other allotropic forms of nonmetallic elements are known, either under pressure or in monolayers. Under sufficiently high pressures, at least half of the nonmetallic elements that are semiconductors or insulators,[n 26] starting with phosphorus at 1.7 GPa, have been observed to form metallic allotropes.[237][n 27] Single layer two-dimensional forms of nonmetals include borophene (boron), graphene (carbon), silicene (silicon), phosphorene (phosphorus), germanene (germanium), arsenene (arsenic), antimonene (antimony) and tellurene (tellurium), collectively referred to as "xenes".[239]

## Abundance, occurrence, extraction and cost

### Abundance

Hydrogen and helium are estimated to make up approximately 99% of all ordinary matter in the universe and over 99.9% of its atoms.[9] Oxygen is thought to be the next most abundant element, at ca. 0.1%.[240] Less than five per cent of the universe is believed to be made of ordinary matter, represented by stars, planets and living beings. The balance is made of dark energy and dark matter, both of which are currently poorly understood.[241]

Five nonmetals—hydrogen, carbon, nitrogen, oxygen and silicon—constitute the bulk of the Earth's crust, atmosphere, oceans and biomass, by weight. The crust is largely made up of oxygen (61%) and silicon (20%); the atmosphere is about 78% nitrogen and 21% oxygen; water (H2O) is oxygen and hydrogen, and the world's biomass largely (99.5%) comprises hydrogen, carbon, and oxygen.[10][11][242]

### Occurrence

#### Noble gases

About 1015 tonnes of noble gases are present in the Earth's atmosphere.[243] Helium is additionally found in natural gas to the extent of as much as 7%.[244] Radon further diffuses out of rocks, where it is formed during the natural decay sequence of uranium and thorium.[245] In 2014, it was reported that the Earth's core may contain ca. 1013 tons of xenon, in the form of stable XeFe3 and XeNi3 intermetallic compounds. This may explain why "studies of the Earth's atmosphere have shown that more than 90% of the expected amount of Xe is depleted."[246]

#### Nonmetal halogens

The nonmetal halogens are found in salt-related minerals. Fluorine occurs in fluorite, this being a widespread mineral. Chlorine, bromine and iodine are found in brines. Exceptionally, a 2012 study reported the presence of 0.04% native fluorine (F
2
) by weight in antozonite, attributing these inclusions to radiation from the presence of tiny amounts of uranium.[247]

#### Unclassified nonmetals

Carbon as diamond, here shown in native form. Diamantine carbon is thermodynamically less stable than graphitic carbon.[248]

Unclassified nonmetals occur typically occur in elemental forms (oxygen, sulfur) or are found in association with either of these two elements:[249]

• Hydrogen occurs in the world's oceans as a component of water, and in natural gas as a component of methane and hydrogen sulfide.[250]
• Carbon occurs in limestone, dolomite, and marble, as carbonates.[251] Less well known is carbon as graphite, which mainly occurs in metamorphic silicate rocks[252] as a result of the compression and heating of sedimentary carbon compounds.
• Oxygen is found in the atmosphere; in the oceans as a component of water; and in the crust as oxide minerals.
• Phosphorus minerals are widespread, usually as phosphorus-oxygen phosphates.[253]
• 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.[254]
• Selenium occurs in metal sulfide ores, where it partially replaces the sulfur;[255] elemental selenium is occasionally found.

#### Metalloids

The metalloids tend to be found in forms combined with oxygen or sulfur or, in the case of tellurium, gold or silver.[249] Boron is found in boron-oxygen borate minerals including in volcanic spring waters. Silicon occurs in the silicon-oxygen mineral silica (sand). Germanium, arsenic and antimony are mainly found as components of sulfide ores. Tellurium occurs in telluride minerals of gold or silver. Native forms of arsenic, antimony and tellurium have been reported.[256]

### Extraction

Nonmetals, and metalloids, are extracted in their raw forms from:[158]

• brine—chlorine, bromine, iodine;
• liquid air—nitrogen, oxygen, neon, argon, krypton, xenon;
• minerals—boron (borate minerals); carbon (coal; diamond; graphite); fluorine (fluorite); silicon (silica); phosphorus (phosphates); antimony (stibnite, tetrahedrite); iodine (in sodium iodate and sodium iodide);
• natural gas—hydrogen, helium, sulfur; and
• ores, as processing byproducts—germanium (zinc ores); arsenic (copper and lead ores); selenium, tellurium (copper ores); and radon (uranium-bearing ores).

As at January 2022, while non-radioactive nonmetals are relatively inexpensive[n 28] there are some exceptions. Boron, germanium, arsenic, and bromine can cost from about US$3 to$11 per gram (cf. silver at about $0.75 per gram). Prices can fall dramatically if bulk quantities are involved.[257] Black phosphorus is produced only in gram quantities by boutique suppliers—a single crystal produced via chemical vapor transport can cost up to$1,000 per gram (ca. fifteen times the cost of gold); in contrast, red phosphorus costs about 50 cents a gram or $227 a pound.[258] Up to 2013, radon was available from the National Institute of Standards and Technology for$1,636 per 0.2 ml unit of issue, equivalent to ca. $86,000,000 per gram, with no indication of a discount for bulk quantities).[259] ## Shared uses Nearly all nonmetals have varying uses in household items; lasers and lighting; and medicine and pharmaceuticals. Nitrogen, for example, is found in some garden treatments; lasers; and diabetes medicines. Germanium, arsenic, and radon each have uses in one or two of these fields but not all three.[158] Aside from the noble gases most of the remaining nonmetals have, or have had, uses in agrochemicals and dyestuffs.[158] To the extent that metalloids show metallic character, they have speciality uses extending to (for example) oxide glasses, alloying components, and semiconductors.[260] Further shared uses of different subsets of the nonmetals encompass their presence in, or specific uses in the fields of air replacements; cryogenics and refrigerants; fertilizers; flame retardants or fire extinguishers; mineral acids; plug-in hybrid vehicles; welding gases; and smart phones.[158] ## Discovery The Alchemist Discovering Phosphorus (1771) by Joseph Wright. The alchemist is Hennig Brand; the glow emanates from the combustion of phosphorus inside the flask. The majority of nonmetals were discovered in the 18th and 19th centuries. Before then carbon, sulfur and antimony were known in antiquity; arsenic was discovered during the Middle Ages (by Albertus Magnus); and Hennig Brand isolated phosphorus from urine in 1669. Helium (1868) holds the distinction of being the first (and so far only) element not discovered on Earth[n 29] while radon was the most recently discovered nonmetal, being discovered only at the end of the 19th century.[158] Chemistry- or physics-based techniques used in the isolation efforts were spectroscopy, fractional distillation, radiation detection, electrolysis, ore acidification, combustion, displacement reactions, and heating, while a few nonmetals occurred naturally as free elements: • Of the noble gases, helium was detected via its yellow line in the coronal spectrum of the sun, and later by observing the bubbles escaping from uranite UO2 dissolved in acid; neon through xenon were obtained via fractional distillation of air; and radon was first observed emanating from compounds of thorium, three years after Henri Becquerel's discovery of radiation in 1896.[262] • The nonmetal halogens were obtained from their halides via electrolysis, adding an acid, or displacement. Some chemists died as a result of their experiments trying to isolate fluorine.[263] • Among unclassified nonmetals, carbon was known (or produced) as charcoal, soot, graphite and diamond; nitrogen was observed in air from which oxygen had been removed; oxygen was obtained by heating mercurous oxide; phosphorus was liberated by heating ammonium sodium hydrogen phosphate (Na(NH4)HPO4), as found in urine;[264] sulfur occurred naturally as a free element; and selenium[n 30] was detected as a residue in sulfuric acid.[266] • Most of the elements commonly recognized as metalloids were isolated by heating their oxides (boron, silicon, arsenic, tellurium) or a sulfide (germanium).[158] Antimony was known in its native form as well as being isolable by heating its sulfide.[267] ## See also ## Notes 1. ^ Hydrogen has historically been placed over one or more of lithium, boron,[3] carbon, or fluorine[4]; or over no group at all; or over all main groups simultaneously, and therefore may or may not be adjacent to other nonmetals.[5] 2. ^ Exceptions are carbon as graphite, which is a good conductor of electricity along its planes; carbon in its less stable diamantine form, which is an excellent conductor of heat (and which explains why diamonds are cool to the touch); and arsenic and antimony, which are sometimes regarded as nonmetals and which are good conductors of electricity 3. ^ With nitric acid, gallium and bismuth form nitrates 4. ^ A.The maximum possible packing efficiency is 74% (see Kepler conjecture). B. The packing efficiency of Br (15%) is determined by dividing the volume of one mole of atoms by the applicable molar volume. The volume of one mole of bromine atoms is given by the volume of one atom multiplied by the Avogadro's number, that is, 6.0221409×1023. The volume of one bromine atom is ${\displaystyle {\frac {4}{3}}\pi r^{3}}$. The bond distance in solid bromine is 2.2836 Å and 2.27±0.10 Å in the gas, giving an atomic radius r of ca. 1.14 Å.[62] C. In comparison, mercury has a packing efficiency of 58.5%.[63] 5. ^ 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. The remaining reactive nonmetallic elements have giant covalent structures, but for H which is a diatomic gas.[89] The single dagger nonmetals N, S and iodine are somewhat hobbled as "strong" nonmetals. While N has a high electronegativity, it is a reluctant anion former,[90] and a pedestrian oxidizing agent unless combined with a more active non-metal like O or F.[91] S reacts in the cold with alkalic and post-transition metals, and Cu, Ag and Hg,[92] 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.[93] Iodine is sufficiently corrosive to cause lesions resembling thermal burns, if handled without suitable protection,[94] and tincture of iodine will smoothly dissolve Au.[95] That said, while F, Cl and Br will all oxidize Fe2+ (aq) to Fe3+...iodine...is such a [relatively] weak oxidizing agent that it cannot remove electrons from Fe(II) ions to form Fe(III) ions."[96] Thus, for the reaction X2 + 2e → 2X(aq) the reduction potentials are F +2.87 V; Cl +1.36; Br +1.09; I +0.54. Here Fe3+ + e → Fe3+ +0.77.[97] Thus F2, Cl2 and Br2 will oxidize Fe2+ to Fe3+ but Fe3+ will oxidize I to I2. Iodine has previously been referred to as a moderately strong oxidizing agent.[98] 6. ^ The quote marks are not found in the source; they are used here to make it clear that the source employs the word «nonmetals» as a formal term for the subset of chemical elements in question, rather than applying to nonmetals generally. 7. ^ 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.[117] 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". 8. ^ Jones[121] takes a philosophical or pragmatic view to these questions. He writes: "Though classification is an essential feature of all branches of science, there are always hard cases at the boundaries. The boundary of a class is rarely sharp... Scientists should not lose sleep over the hard cases. As long as a classification system is beneficial to economy of description, to structuring knowledge and to our understanding, and hard cases constitute a small minority, then keep it. If the system becomes less than useful, then scrap it and replace it with a system based on different shared characteristics". 9. ^ Metal oxides are usually ionic.[136] On the other hand, high valence oxides of metals are usually either polymeric or covalent.[137] A polymeric oxide has a linked structure composed of multiple repeating units.[138] 10. ^ 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.[144] 11. ^ 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.[150] 12. ^ Greenwood[167] commented that: "The extent to which metallic elements mimic boron (in having fewer electrons than orbitals available for bonding) has been a fruitful cohering concept in the development of metalloborane chemistry ... Indeed, metals have been referred to as "honorary boron atoms" or even as "flexiboron atoms". The converse of this relationship is clearly also valid ..." 13. ^ The BH3 and Fe(CO4) species in these reactions are short-lived reaction intermediates.[169] 14. ^ See also Properties of metals, metalloids and nonmetals, which treats metalloids as a class of their own 15. ^ Carbon as exfoliated (expanded) graphite,[182] and as meter-long carbon nanotube wire;[183] phosphorus as white phosphorus (soft as wax, pliable and can be cut with a knife, at room temperature);[184] sulfur as plastic sulfur;[185] and selenium as selenium wires[186] 16. ^ Metals have electrical conductivity values of from 6.9×103 S•cm−1 for manganese to 6.3×105 for silver.[188] 17. ^ Metalloids have electrical conductivity values of from 1.5×10−6 S•cm−1 for boron to 3.9×104 for arsenic.[189] 18. ^ Unclassified nonmetals have electrical conductivity values of from ca. 1×10−18 S•cm−1 for the elemental gases to 3±4 in graphite.[190] 19. ^ The nonmetal halogens have electrical conductivity values of from ca. 1×10−18 S•cm−1 for F and Cl to 1.7×10−8 S•cm−1 for iodine.[190][191] 20. ^ The elemental gases have electrical conductivity values of ca. 1×10−18 S•cm−1[190] 21. ^ They always give compounds less acidic in character than the corresponding compounds of the typical nonmetals[195] 22. ^ Values for the noble gases are from Allen and Huheey.[200] 23. ^ Disodium helide (Na2He) is a compound of helium and sodium that is stable at high pressures above 113 GPa. Argon forms an alloy with nickel, at 140 GPa and close to 1,500 K however at this pressure argon is no longer a noble gas.[205] 24. ^ Arsenic trioxide reacts with sulfur trioxide, forming arsenic "sulfate" As2(SO4)3[212] 25. ^ CO and N2O are "formally the anhydrides of formic and hyponitrous acid, respectively: CO + H2O → H2CO2 (HCOOH, formic acid); N2O + H2O → H2N2O2 (hyponitrous acid)".[216] 26. ^ B; Si, Ge; N, P; O, S, Se, Te; nonmetal halogens; and the noble gases[192] 27. ^ As at 2020, high pressure studies and experiments were said to represent, "a very active and vigorous research field".[238] 28. ^ Costs for most nonmetals ranged from US$0.0002 per gram for bulk oxygen to \$1.90 per gram for bulk fluorine.[257]
29. ^ Helium acquired the "-ium" suffix as its discoverer, William Lockyer, wrote: "I took upon myself the responsibility of coining the word helium... I did not know whether the substance ... was a metal like calcium or a gas like hydrogen, but I did know that it behaved like hydrogen [being found in the sun] and that hydrogen, as Dumas had stated, behaved as a metal".[261]
30. ^ Berzelius, who discovered selenium, thought it had the properties of a metal, combined with those of sulfur.[265]

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