Nonmetal: Difference between revisions

This article is about the elements which are not metallic when solid. For other uses, see Nonmetal (astrophysics) and Nonmetal (physics).

Nonmetals in their periodic table context

always/usually considered nonmetals

metalloids, sometimes considered nonmetals

status as nonmetal or metal unconfirmed

Nonmetals or non-metallic elements are chemical elements that have high electronegativity and mostly lack distinctive metallic properties. They range from colorless gases like hydrogen to shiny crystals like iodine. Physically, they are usually lighter (less dense) than metals and are often poor conductors of heat and electricity. Since nonmetals have high electronegativity they usually attract electrons in a chemical bond with another element, and their oxides tend to be acidic.

Seventeen elements are 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 the observable universe. Five nonmetallic elements—hydrogen, carbon, nitrogen, oxygen, and silicon—make up the bulk of Earth's oceans, atmosphere, biosphere, and are in compounds in the crust.

Industrial uses of nonmetals include in electronics, energy storage, agriculture, and chemical production.

Most nonmetallic elements were identified in the 18th and 19th centuries. While a distinction between metals and other minerals had existed since antiquity, the classification of chemical elements as metallic or nonmetallic emerged only in the late 18th century. Since then over two dozen properties have been suggested as criteria for distinguishing nonmetals from metals.

Definition and applicable elements

Unless otherwise noted, this article describes the most stable form of an element in ambient conditions.

While arsenic (here sealed in a container to prevent tarnishing) has a shiny appearance and is a reasonable conductor of heat and electricity, it is soft and brittle and its chemistry is predominately nonmetallic.

Nonmetallic chemical elements are generally described as lacking properties common to metals, namely shininess, pliability, good thermal and electrical conductivity, and a general capacity to form basic oxides. There is no widely-accepted precise definition; any list of nonmetals is open to debate and revision. The elements included depend on the properties regarded as most representative of nonmetallic or metallic character.

Fourteen elements are almost always recognized as nonmetals:

• Hydrogen
• Nitrogen
• Oxygen
• Sulfur

• Fluorine
• Chlorine
• Bromine
• Iodine

• Helium
• Neon
• Argon
• Krypton
• Xenon
• Radon

Three more are commonly classed as nonmetals, but some sources list them as "metalloids", a term which refers to elements regarded as intermediate between metals and nonmetals:

• Carbon
• Phosphorus
• Selenium

One or more of the six elements most commonly recognized as metalloids are sometimes instead counted as nonmetals:

• Boron
• Silicon
• Germanium
• Arsenic
• Antimony
• Tellurium

About 15–20% of the 118 known elements are thus classified as nonmetals.

General properties

Physical

See also § Physical properties by element type

Variety in color and form
of some nonmetallic elements

Boron in its β-rhombohedral phase

Metallic appearance of carbon as graphite

Blue color of liquid oxygen

Pale yellow liquid fluorine in a cryogenic bath

Sulfur as yellow chunks

Liquid bromine at room temperature

Metallic appearance of iodine under white light

Liquefied xenon

Nonmetals vary greatly in appearance, being colorless, colored or shiny. For the colorless nonmetals (hydrogen, nitrogen, oxygen, and the noble gases), their electrons are held sufficiently strongly so that no absorption of light happens in the visible part of the spectrum, and all visible light is transmitted. 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". The shininess of boron, graphitic carbon, silicon, black phosphorus, germanium, arsenic, selenium, antimony, tellurium, and iodine is a result of their structures featuring varying degrees of delocalized (free-moving) electrons that scatter incoming visible light.

About half of nonmetallic elements are gases; 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. The solid nonmetals have low densities and low mechanical and structural strength (being brittle or crumbly), and a wide range of electrical conductivity.

This diversity in form stems from variability in internal structures and bonding arrangements. 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. In contrast, nonmetals that form giant structures, such as chains of up to 1,000 selenium atoms, sheets of carbon atoms in graphite, or three-dimensional lattices of silicon atoms have higher melting and boiling points, and are all solids, as it takes more energy to overcome their stronger covalent bonds. Nonmetals closer to the left or bottom of the periodic table (and so closer to the metals) often have some weak metallic interactions between their molecules, chains, or layers; this occurs in boron, carbon, phosphorus, arsenic, selenium, antimony, tellurium and iodine.

Some general physical
differences between metals and nonmetals

Aspect	Metals	Nonmetals
Appearance and form	Shiny if freshly prepared or fractured; few colored; all but one solid	Shiny, colored or transparent; all but one solid or gaseous
Density	Often higher	Often lower
Elasticity	Mostly malleable and ductile	Brittle if solid
Electrical conductivity	Good	Poor to good
Electronic structure	Metallic or semimetalic	Semimetallic, semiconductor, or insulator

The structures of nonmetallic elements differ from those of metals primarily due to variations in valence electron numbers and atomic size. Metals typically have fewer valence electrons than available orbitals, leading them to share electrons with many nearby atoms, resulting in centrosymmetrical crystalline structures. In contrast, nonmetals share only the electrons required to achieve a noble gas electron configuration. 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. Antimony's larger atomic size prevents triple bonding, resulting in buckled layers in which each antimony atom is singly bonded with three other nearby atoms.

The electrical and thermal conductivities of nonmetals, along with the brittle nature of solid nonmetals, are likewise related to their internal arrangements. Whereas good conductivity and plasticity (malleability, ductility) are ordinarily associated with the presence of free-moving and evenly distributed electrons in metals, the electrons in nonmetals typically lack such mobility. Among nonmetallic elements, good electrical and thermal conductivity is seen only in carbon (as graphite, along its planes), arsenic, and antimony. Good thermal conductivity otherwise occurs only in boron, silicon, phosphorus, and germanium; such conductivity is transmitted though vibrations of the crystalline lattices of these elements. Moderate electrical conductivity is observed in the semiconductors boron, silicon, phosphorus, germanium, selenium, tellurium, and iodine. Plasticity occurs under limited circumstances in carbon, as seen in exfoliated (expanded) graphite and carbon nanotube wire, in white phosphorus (soft as wax, pliable and can be cut with a knife, at room temperature), in plastic sulfur, and in selenium which can be drawn into wires from its molten state.

The physical differences between metals and nonmetals arise from internal and external atomic forces. Internally, the positive charge stemming from the protons in an atom's nucleus acts to hold the atom's outer electrons in place. Externally, the same electrons are subject to attractive forces from protons in neighboring atoms. When the external forces are greater than, or equal to, the internal force, the outer electrons are expected to become relatively free to move between atoms, and metallic properties are predicted. Otherwise nonmetallic properties are expected.

Allotropes

Three allotropes of carbon

a transparent electrical insulator

a brownish semiconductor

a blackish conductor

Diamond, buckminsterfullerene, and graphite

For a more comprehensive list, see Allotropy § Non-metals, and Single-layer materials.

Over half of the nonmetallic elements exhibit a range of less stable allotropic forms, each with distinct physical properties. For example, carbon, the most stable form of which is graphite, can manifest as diamond, buckminsterfullerene, and amorphous and paracrystalline (mixed amorphous and crystalline) variations. Allotropes also occur for nitrogen, oxygen, phosphorus, sulfur, selenium, the six metalloids, and iodine.

Chemical

See also § Chemical properties by element type

Some general chemistry-based
differences between metals and nonmetals

Aspect		Metals	Nonmetals
Reactivity		Wide range: very reactive to noble
Oxides	lower	Basic	Acidic; never basic
	higher	Increasingly acidic
Compounds with metals		Alloys	Ionic compounds
Ionization energy		Low to high	Moderate to very high
Electronegativity		Low to high	Moderate to very high

Nonmetals have relatively high values of electronegativity, and their oxides are therefore usually acidic. Exceptions may occur if a nonmetal is not very electronegative, or if its oxidation state is low, or both. These non-acidic oxides of nonmetals may be amphoteric (like water, H₂O) or neutral (like nitrous oxide, N₂O), but never basic (as is common with metals).

Nonmetals tend to gain or share electrons during chemical reactions, in contrast to metals which tend to donate electrons. This behavior is closely related to the stability of electron configurations in the noble gases, which have complete outer shells. Nonmetals generally gain enough electrons to attain the electron configuration of the following noble gas, while metals tend to lose electrons, in some cases achieving the electron configuration of the preceding noble gas. These tendencies in nonmetallic elements are succinctly summarized by the duet and octet rules of thumb.

They typically exhibit higher ionization energies, electron affinities, and standard electrode potentials than metals. Generally, the higher these values are (including electronegativity) the more nonmetallic the element tends to be. For example, the chemically very active nonmetals fluorine, chlorine, bromine, and iodine have an average electronegativity of 3.19—a figure higher than that of any individual metal. On the other hand, the 2.05 average of the chemically weak metalloid nonmetals falls within the 0.70 to 2.54 range of metals.

The chemical distinctions between metals and nonmetals primarily stem 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 in tandem with the number of protons in the atomic nucleus. Consequently, there is a corresponding reduction in atomic radius as the heightened nuclear charge draws the outer electrons closer to the nucleus core. In metals, the impact of the nuclear charge is generally weaker compared to nonmetallic elements. As a result, in chemical bonding, metals tend to lose electrons, leading to the formation of positively charged ions or polarized atoms, while nonmetals tend to gain these electrons due to their stronger nuclear charge, resulting in negatively charged ions or polarized atoms.

The number of compounds formed by nonmetals is vast. The first 10 places in a "top 20" table of elements most frequently encountered in 895,501,834 compounds, as listed in the Chemical Abstracts Service register for November 2, 2021, were occupied by nonmetals. Hydrogen, carbon, oxygen, and nitrogen collectively appeared in most (80%) of compounds. Silicon, a metalloid, ranked 11th. The highest-rated metal, with an occurrence frequency of 0.14%, was iron, in 12th place. A few examples of nonmetal compounds are: boric acid (H
₃BO
₃), used in ceramic glazes; selenocysteine (C
₃H
₇NO
₂Se), the 21st amino acid of life; phosphorus sesquisulfide (P₄S₃), found in strike anywhere matches; and teflon ((C
₂F
₄)_n), used to create non-stick coatings for pans and other cookware.

Complications

Adding complexity to the chemistry of the nonmetals are anomalies occurring in the first row of each periodic table block; non-uniform periodic trends; higher oxidation states; multiple bond formation; and property overlaps with metals.

First row anomaly

Condensed periodic table highlighting the first row of each block:  s   p   d  and  f

Period

s-block

1

H 1

He 2

p-block

2

Li 3

Be 4

B 5

C 6

N 7

O 8

F 9

Ne 10

3

Na 11

Mg 12

d-block

Al 13

Si 14

P 15

S 16

Cl 17

Ar 18

4

K 19

Ca 20

Sc-Zn 21-30

Ga 31

Ge 32

As 33

Se 34

Br 35

Kr 36

5

Rb 37

Sr 38

f-block

Y-Cd 39-48

In 49

Sn 50

Sb 51

Te 52

I 53

Xe 54

6

Cs 55

Ba 56

La-Yb 57-70

Lu-Hg 71-80

Tl 81

Pb 82

Bi 83

Po 84

At 85

Rn 86

7

Fr 87

Ra 88

Ac-No 89-102

Lr-Cn 103-112

Nh 113

Fl 114

Mc 115

Lv 116

Ts 117

Og 118

Group

(1)

(2)

(3-12)

(13)

(14)

(15)

(16)

(17)

(18)

The first-row anomaly strength by block is s >> p > d > f.

Starting with hydrogen, the first row anomaly primarily arises from the electron configurations of the elements concerned. Hydrogen is particularly notable for its diverse bonding behaviors. It most commonly forms covalent bonds, but it can also lose its single electron in an aqueous solution, leaving behind a bare proton with tremendous polarizing power. Consequently, this proton can attach itself to the lone electron pair of an oxygen atom in a water molecule, laying the foundation for acid-base chemistry. Moreover, a hydrogen atom in a molecule can form a second, albeit weaker, bond with an atom or group of atoms in another molecule. Such bonding, "helps give snowflakes their hexagonal symmetry, binds DNA into a double helix; shapes the three-dimensional forms of proteins; and even raises water's boiling point high enough to make a decent cup of tea."

Hydrogen and helium, as well as boron through neon, have unusually small atomic radii. This phenomenon arises because the 1s and 2p subshells lack inner analogues (meaning 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. As a result, ionization energies and electronegativities among these elements are higher than what periodic trends would otherwise suggest. The compact atomic radii of carbon, nitrogen, and oxygen facilitate the formation of double or triple bonds.

While it would normally be expected, on electron configuration consistency grounds, that hydrogen and helium would be placed atop the s-block elements, the significant first row anomaly shown by these two elements justifies alternative placements. Hydrogen is occasionally positioned above fluorine, in group 17, rather than above lithium in group 1. Helium is commonly placed above neon, in group 18, rather than above beryllium in group 2.

Secondary periodicity

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

An alternation in certain periodic trends, sometimes referred to as secondary periodicity, becomes evident when descending groups 13 to 15, and to a lesser extent, groups 16 and 17. Immediately after the first row of d-block metals, from scandium to zinc, the 3d electrons in the p-block elements—specifically, gallium (a metal), germanium, arsenic, selenium, and bromine—prove less effective at shielding the increasing positive nuclear charge. This same effect is observed with the emergence of fourteen f-block metals located between barium and lutetium, ultimately leading to atomic radii that are smaller than expected for elements from hafnium (Hf) onward.

The Soviet chemist Shchukarev gives two more tangible examples:

"The toxicity of some arsenic compounds, and the absence of this property in analogous compounds of phosphorus [P] and antimony [Sb]; and the ability of selenic acid [H₂SeO₄] to bring metallic gold [Au] into solution, and the absence of this property in sulfuric [H₂SO₄] and [H₂TeO₄] acids."

Higher oxidation states

Roman numerals such as III, V and VIII denote oxidation states

Some nonmetallic elements exhibit oxidation states that deviate from those predicted by the octet rule, which typically results in a valency of –3 in group 15, –2 in group 16, –1 in group 17, and 0 in group 18. Examples of such typical states can include compounds like ammonia N(III)H₃, hydrogen sulfide(II) H₂S, hydrogen fluoride(I) HF, and elemental xenon(0) Xe. Meanwhile, the maximum possible oxidation state increases from +5 in group 15, to +8 in group 18. The +5 oxidation state is observable from period 2 onward, in compounds such as nitric acid HN(V)O₃ and phosphorus pentafluoride PCl₅. Higher oxidation states in later groups emerge from period 3 onwards, as seen in sulfur hexafluoride SF₆, iodine heptafluoride IF₇, and xenon(VIII) tetroxide XeO₄. For heavier nonmetals, their larger atomic radii and lower electronegativity values enable the formation of compounds with higher oxidation numbers, supporting higher bulk coordination numbers.

Multiple bond formation

Molecular structure of pentazenium, a homopolyatomic cation of nitrogen with the formula N₅⁺ and structure N−N−N−N−N.

Period 2 nonmetals, particularly carbon, nitrogen, and oxygen, show a propensity to form multiple bonds. The compounds formed by these elements often exhibit unique stoichiometries and structures, as seen in the various nitrogen oxides, which are not commonly found in elements from later periods.

Property overlaps

While certain elements have traditionally been classified as nonmetals and others as metals, some overlapping of properties occurs. Writing early in the twentieth century, by which time the era of modern chemistry had been well-established, Humphrey observed that:

... these two groups, however, are not marked off perfectly sharply from each other; some nonmetals resemble metals in certain of their properties, and some metals approximate in some ways to the non-metals.

Boron (here in its less stable amorphous form) shares some similarities with metals

Examples of metal-like properties occurring in nonmetallic elements include:

• silicon has an electronegativity (1.9) comparable with metals such as cobalt (1.88), copper (1.9), nickel (1.91) and silver (1.93);
• the electrical conductivity of graphite exceeds that of some metals;
• selenium can be drawn into a wire;
• radon is the most metallic of the noble gases and begins to show some cationic behavior, which is unusual for a nonmetal; and
• in extreme conditions, just over half of nonmetallic elements can form homopolyatomic cations.

Examples of nonmetal-like properties occurring in metals are:

• Tungsten displays some nonmetallic properties, being brittle, having a high electronegativity, and forming only anions in aqueous solution, and predominately acidic oxides. These are characteristics more aligned with nonmetals. Even so, tungsten is classified as a metal, illustrating the spectrum of behaviors elements can exhibit within their classifications.
• Gold, the "king of metals" demonstrates several nonmetallic behaviors. It has the highest electrode potential among metals, suggesting a preference for gaining rather than losing electrons. Gold's ionization energy is one of the highest among metals, and its electron affinity and electronegativity are high, with the latter exceeding that of some nonmetals. It forms the Au^– auride anion and exhibits a tendency to bond to itself, behaviors which are unexpected for metals. In aurides (MAu, where M = Li–Cs), gold's behavior is similar to that of a halogen, thereby bridging the traditional metal-nonmetal divide.

A relatively recent development involves certain compounds of heavier p-block elements, such as silicon, phosphorus, germanium, arsenic and antimony, exhibiting behaviors typically associated with transition metal complexes. This phenomenon is linked to a small energy gap between their filled and empty molecular orbitals, which are the regions in a molecule where electrons reside and where they can be available for chemical reactions. In such compounds, this closer energy alignment allows for unusual reactivity with small molecules like hydrogen (H₂), ammonia (NH₃), and ethylene (C₂H₄), a characteristic previously observed primarily in transition metal compounds. These reactions may open new avenues in catalytic applications.

Types

Nonmetal classification schemes vary widely, with some accommodating as few as two subtypes and others identifying up to seven. For example, the periodic table in the Encyclopaedia Britannica recognizes noble gases, halogens, and other nonmetals, and splits the elements commonly recognized as metalloids between "other metals" and "other nonmetals". On the other hand, seven of twelve color categories on the Royal Society of Chemistry periodic table include nonmetals.

		Group (1, 13−18)				Period
	13	14	15	16	1/17	18	(1−6)
					H	He	1
	B	C	N	O	F	Ne	2
		Si	P	S	Cl	Ar	3
		Ge	As	Se	Br	Kr	4
			Sb	Te	I	Xe	5
						Rn	6

Starting on the right side of the periodic table, three types of nonmetals can be recognized:

   the relatively inert noble gases—helium, neon, argon, krypton, xenon, radon;

   the notably reactive halogen nonmetals—fluorine, chlorine, bromine, iodine; and

   the mixed reactivity "unclassified nonmetals", a set with no widely used collective name—hydrogen, carbon, nitrogen, oxygen, phosphorus, sulfur, selenium. The descriptive phrase unclassified nonmetals is used here for convenience.

The elements in a fourth set are sometimes recognized as nonmetals:

   the generally unreactive metalloids, sometimes considered a third category distinct from metals and nonmetals—boron, silicon, germanium, arsenic, antimony, tellurium.

While many of the early workers attempted to classify elements none of their classifications were satisfactory. They were divided into metals and nonmetals, but some were soon found to have properties of both. These were called metalloids. This only added to the confusion by making two indistinct divisions where one existed before.

Whiteford & Coffin 1939, Essentials of College Chemistry

The boundaries between these types are not sharp. Carbon, phosphorus, selenium, and iodine border the metalloids and show some metallic character, as does hydrogen.

The greatest discrepancy between authors occurs in metalloid "frontier territory". Some consider metalloids distinct from both metals and nonmetals, while others classify them as nonmetals. Some categorize certain metalloids as metals (e.g., arsenic and antimony due to their similarities to heavy metals). Metalloids resemble the elements universally considered "nonmetals" in having relatively low densities, high electronegativity, and similar chemical behavior.

For context, the metallic side of the periodic table also ranges widely in reactivity. Highly reactive metals fill most of the s- and f-blocks on the left, bleeding into the early part of the d-block. Thereafter, reactivity generally decreases closer to the p-block, whose metals are not particularly reactive. The very unreactive noble metals, such as platinum and gold, are clustered in an island within the d-block.

Noble gases

Main article: Noble gas

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

Six nonmetals are classified as noble gases: helium, neon, argon, krypton, xenon, and the radioactive radon. In conventional periodic tables they occupy the rightmost column. They are called noble gases due to their exceptionally low chemical reactivity.

These elements exhibit remarkably similar properties, characterized by their colorlessness, odorlessness, and nonflammability. Due to their closed outer electron shells, noble gases possess feeble interatomic forces of attraction, leading to exceptionally low melting and boiling points. As a consequence, they all exist as gases under standard conditions, even those with atomic masses surpassing many typically solid elements.

Chemically, the noble gases exhibit relatively high ionization energies, negligible or negative electron affinities, and high to very high electronegativities. The number of compounds formed by noble gases is in the hundreds and continues to expand, with most of these compounds involving the combination of oxygen or fluorine with either krypton, xenon, or radon.

Halogen nonmetals

See also: Halogen

Highly reactive sodium metal (Na, left) combines with corrosive halogen nonmetal chlorine gas (Cl, right) to form stable, unreactive table salt (NaCl, center).

While the halogen nonmetals are notably reactive and corrosive elements, they can also be found in everyday compounds like toothpaste (NaF); common table salt (NaCl); swimming pool disinfectant (NaBr); and food supplements (KI). The term "halogen" itself means "salt former".

Physically, fluorine and chlorine exist as pale yellow and yellowish-green gases, respectively, while bromine is a reddish-brown liquid, typically covered by a layer of its fumes; iodine is a solid and under white light is metallic-looking. Electrically, the first three elements function as insulators while iodine behaves as a semiconductor (along its planes).

Chemically, the halogen nonmetals exhibit high ionization energies, electron affinities, and electronegativity values, and are mostly relatively strong oxidizing agents. These characteristics contribute to their corrosive nature. All four elements tend to form primarily ionic compounds with metals, in contrast to the remaining nonmetals (except for oxygen) which tend to form primarily covalent compounds with metals. The highly reactive and strongly electronegative nature of the halogen nonmetals epitomizes nonmetallic character.

Unclassified nonmetals

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

After classifying the nonmetallic elements into noble gases and halogens, but before encountering the metalloids, there are seven nonmetals: hydrogen, carbon, nitrogen, oxygen, phosphorus, sulfur, and selenium.

In their most stable forms, three of these are colorless gases (hydrogen, nitrogen, oxygen); three are metallic looking solids (carbon, phosphorus, selenium); and one is a yellow solid (sulfur). Electrically, graphitic carbon behaves as a semimetal along its planes and a semiconductor perpendicular to its planes; phosphorus and selenium are semiconductors; while hydrogen, nitrogen, oxygen, and sulfur are insulators.

These elements are often considered too diverse to merit a collective name, and have been referred to as other nonmetals, or simply as nonmetals. As a result, their chemistry is typically taught disparately, according to their respective periodic table groups: hydrogen in group 1; the group 14 nonmetals (including carbon, and possibly silicon and germanium); the group 15 nonmetals (including nitrogen, phosphorus, and possibly arsenic and antimony); and the group 16 nonmetals (including oxygen, sulfur, selenium, and possibly tellurium). Authors may choose other subdivisions based on their preferences.

Hydrogen, in particular, behaves in some respects like a metal and in others like a nonmetal. Like a metal it can, for example, form a solvated cation in aqueous solution; it can substitute for alkali metals in compounds such as the chlorides (NaCl cf. HCl) and nitrates (KNO₃ cf. HNO₃), and in certain alkali metal organometallic structures; and it can form alloy-like hydrides with some transition metals. Conversely, it is an insulating diatomic gas, akin to the nonmetals nitrogen, oxygen, fluorine and chlorine. In chemical reactions, it tends to ultimately attain the electron configuration of helium (the following noble gas) behaving in this way as a nonmetal. It attains this configuration by forming a covalent or ionic bond or, if it has initially given up its electron, by attaching itself to a lone pair of electrons.

Some or all of these nonmetals share several properties. Being generally less reactive than the halogens, most of them can occur naturally in the environment. They have significant roles in biology and geochemistry. Collectively, their physical and chemical characteristics can be described as "moderately non-metallic". However, they all have corrosive aspects. Hydrogen can corrode metals. Carbon corrosion can occur in fuel cells. Acid rain is caused by dissolved nitrogen or sulfur. Oxygen causes iron to corrode via rust. White phosphorus, the most unstable form, ignites in air and leaves behind phosphoric acid residue. Untreated selenium in soils can lead to the formation of corrosive hydrogen selenide gas. When combined with metals, the unclassified nonmetals can form high-hardness (interstitial or refractory) compounds due to their relatively small atomic radii and sufficiently low ionization energies. They also exhibit a tendency to bond to themselves, particularly in solid compounds. Additionally, diagonal periodic table relationships among these nonmetals mirror similar relationships among the metalloids.

Metalloids

Main article: Metalloid

The six elements more commonly recognized as metalloids are boron, silicon, germanium, arsenic, antimony, and tellurium, all of which have a metallic appearance. (Other elements appearing less commonly on lists of metalloids include carbon, aluminium, selenium and polonium; these have both metallic and nonmetallic properties, but one or the other predominates.) In the periodic table, metalloids occupy a diagonal region within the p-block extending from boron at the upper left to tellurium at the lower right, along the dividing line between metals and nonmetals shown on some tables.

Metalloids are brittle and poor-to-good conductors of heat and electricity. Specifically, boron, silicon, germanium, and tellurium are semiconductors. Arsenic and antimony have the electronic band structures of semimetals, although both have less stable semiconducting allotropes: arsenic as arsenolamprite, an extremely rare naturally occurring form; and antimony in its synthetic thin-film amorphous form.

Chemically, 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. Additionally, they tend to form alloys when combined with metals.

Abundance, extraction, and use

Abundance

Approximate composition
(top three components by weight)

Universe	75% hydrogen	23% helium	1% oxygen
Atmosphere	78% nitrogen	21% oxygen	0.5% argon
Hydrosphere	86% oxygen	11% hydrogen	2% chlorine
Biomass	63% oxygen	20% carbon	10% hydrogen
Crust	46% oxygen	27% silicon	8% aluminium

Hydrogen and helium dominate the observable universe, making up an estimated 98% of all ordinary matter by mass. These elements are abundant because they are primary products of nuclear fusion processes in stars. In contrast, heavier nonmetals like xenon are less abundant due to the complex nuclear processes required for their formation. Oxygen, the next most abundant element, accounts for about 1%.

Five nonmetals—hydrogen, carbon, nitrogen, oxygen, and silicon—form the bulk of the directly observable structure of the Earth: about 73% of the crust, 93% of the biomass, 96% of the hydrosphere, and over 99% of the atmosphere, as shown in the accompanying table. Silicon and oxygen form highly stable tetrahedral structures, known as silicates. Here, "the powerful bond that unites the oxygen and silicon ions is the cement that holds the Earth's crust together." In the biomass, the relative abundance of the first four nonmetals (and phosphorus, sulfur, and selenium marginally) is attributed to a combination of relatively small atomic size, and sufficient spare electrons. These two properties enable them to bind to one another and "some other elements, to produce a molecular soup sufficient to build a self-replicating system."

The mantle and core, making up about 99% of the Earth's volume, are estimated to be made up of oxygen (31% by weight) and silicon (16%), with the remainder largely composed of the metals iron (31%), magnesium (15%) and nickel (2%).

The relative scarcity of metals in the more visible parts of Earth (the atmosphere, lithosphere, and hydrosphere) compared to nonmetals can be explained by the difference in their average densities. Metals are generally denser than nonmetals, which caused more of them to sink towards the core during Earth's early molten state. As a result, the less dense nonmetals remained in the outer layers, making them more abundant in the atmosphere, lithosphere, and hydrosphere.

Extraction

Unlike metals, nine of the 23 nonmetallic elements are light enough, or form compounds that are light enough, to be extracted from either natural gas or liquid air. These elements include hydrogen, helium, nitrogen, oxygen, neon, sulfur, argon, krypton, and xenon. For example, nitrogen and oxygen are extracted from air through fractional distillation of liquid air. This method capitalizes on their different boiling points to separate them efficiently. Sulfur was extracted using the Frasch process, which involved injecting superheated water into underground deposits to melt the sulfur, which is then pumped to the surface. This technique leveraged sulfur's low melting point relative to other geological materials. It is now obtained by reacting the hydrogen sulfide in natural gas, with oxygen. Water is formed, leaving the sulfur behind.

Nonmetallic elements are extracted from the following sources:

		Group (1, 13−18)				Period
	13	14	15	16	1/17	18	(1−6)
					H	He	1
	B	C	N	O	F	Ne	2
		Si	P	S	Cl	Ar	3
		Ge	As	Se	Br	Kr	4
			Sb	Te	I	Xe	5
						Rn	6

   Gases (3): hydrogen, from methane; helium, from natural gas; sulfur, from hydrogen sulfide in natural gas

   Liquids (9): nitrogen, oxygen, neon, argon, krypton and xenon from liquid air; chlorine, bromine and iodine from brine

   Solids (12): boron, from borates; carbon occurs naturally as graphite; silicon, from silica; phosphorus, from phosphates; iodine, from sodium iodate; radon, as a decay product from uranium ores; fluorine, from fluorite; germanium, arsenic, selenium, antimony and tellurium, from sulfides.

Uses

Shared uses of nonmetals

Field	Elements
air replacements, inert	H, He, C, N, O, F (in SF6), P, S and Ar
cryogenics and refrigerants	H, He, N, O, F, Ne, S, Cl and Ar
explosives	H, C, N, O, P, S, Cl
fertilizers	H, B, C, N, O, Si, P, S
flame retardants or fire extinguishers	H, B, C (including graphite), N, O, F, Si, P, S, Cl, Ar, Br and Sb
household accoutrements	H (primary constituent of water); He (party balloons); B (in detergents); C (in pencils, as graphite); N (beer widgets); O (as peroxide, in detergents); F (as fluoride, in toothpaste); Ne (lighting); Si (in glassware); P (matches); S (garden treatments); Cl (bleach constituent); Ar (insulated windows); Ge (in wide-angle camera lenses); Se (glass; solar cells); Br (as bromide, for purification of spa water); Kr (energy saving fluorescent lamps); Sb (in batteries); Te (in ceramics, solar panels, rewrite-able DVDs); I (in antiseptic solutions); Xe (in plasma TV display cells, a technology subsequently made redundant by low cost LED and OLED displays)
lasers and lighting	H, He, C (in carbon dioxide lasers, CO2); N, O (in a chemical oxygen iodine laser); F (in a hydrogen fluoride laser, HF); Ne, Si, P, S (in a sulfur lamp); Cl, Ar, Ge, As, Se, Br, Kr, Te, I and Xe
lubricants	H, He, B, C, N, O, F, Si, P, S, Cl, Ar, Se, Sb
medicine and pharmaceuticals	H, He, B, C, N, O, F, Si, P, S, Cl, Ar, As, Se, Br, Kr, Sb, Te, I, Xe and Rn
mineral acids	H, B, C, N, O, F, Si, P, S, Cl, Ge, As, Sb, Br, Te, I and Xe
plug-in hybrid vehicles	H, He, B, C, N, O, F, Si, P, S, Cl, Ar, Br, Sb, Te and I
welding gases	H, He, C (in CO2), N, O, Ar
smart phones	H, He, B, C, N, O, F, Si, P, S, Cl, Ge, As, Se, Br, Sb

The unique properties of nonmetals determine their applications across various industries. For example, carbon in the form of graphite and carbon fiber, has distinct uses. Graphite's high electrical conductivity makes it suitable for use in fuel cells, while carbon fiber is ideal for laminates. Silicon's semiconducting properties are crucial for the electronics industry, where it is used to manufacture integrated circuits and solar cells.

Near universal uses for nonmetals are for household accoutrements; lasers and lighting; and medicine and pharmaceuticals. One or two of germanium, arsenic, and or radon will be absent. To the extent that metalloids show metallic character, they have speciality uses extending to (for example) oxide glasses, alloying components, and semiconductors.

Further shared uses of different subsets of the nonmetals encompass their presence in, or specific uses in the fields of air replacements; cryogenics and refrigerants; explosives; fertilizers; flame retardants or fire extinguishers; lubricants; mineral acids; plug-in hybrid vehicles; welding gases; and smart phones.

• 
  Nitric acid (here colored due to the presence of nitrogen dioxide) is often used in the explosives industry
• 
  A high-voltage circuit-breaker employing sulfur hexafluoride (SF₆) as its inert (air replacement) interrupting medium
• 
  A COIL (chemical oxygen iodine laser) system mounted on a Boeing 747 variant known as the YAL-1 Airborne Laser
• 
  Cylinders containing argon gas for use in extinguishing fire without damaging computer server equipment

History, background, and taxonomy

Discovery

Main article: Timeline of chemical element discoveries

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

While most nonmetallic elements were identified during the 18th and 19th centuries, a few were recognized much earlier. Carbon, sulfur, and antimony were known in antiquity. Arsenic was discovered in the Middle Ages (credited to Albertus Magnus) and phosphorus in 1669 (isolated from urine by Hennig Brand). Helium, identified in 1868, is the only element not initially discovered on Earth itself. The most recently identified nonmetal is radon, detected at the end of the 19th century.

Some nonmetals occur naturally as free elements, others required intricate extraction or isolation procedures. Such procedures included spectroscopy, fractional distillation, radiation detection, electrolysis, ore acidification, displacement reactions, combustion, and controlled heating processes.

The noble gases, renowned for their low reactivity, were first identified via spectroscopy, air fractionation, and radioactive decay studies. Helium was initially detected by its distinctive yellow line in the solar corona spectrum. Subsequently, it was observed escaping as bubbles when uranite UO₂ was dissolved in acid. Neon, argon, krypton, and xenon were obtained through the fractional distillation of air. The discovery of radon occurred three years after Henri Becquerel's pioneering research on radiation in 1896.

The isolation of the halogen nonmetals from their halides involved techniques including electrolysis, acid addition, or displacement. These efforts were not without peril, as some chemists died in their pursuit of isolating fluorine.

The unclassified nonmetals have a diverse history. Hydrogen was discovered and first described in 1671 as the product of the reaction between iron filings and dilute acids. Carbon was found naturally in forms like charcoal, soot, graphite, and diamond. Nitrogen was discovered by examining air after carefully removing oxygen. Oxygen itself was obtained by heating mercurous oxide. Phosphorus was derived from the heating of ammonium sodium hydrogen phosphate (Na(NH₄)HPO₄), a compound found in urine. Sulfur occurred naturally as a free element, simplifying its isolation. Selenium, was first identified as a residue in sulfuric acid.

Most metalloids were first isolated by heating their oxides (boron, silicon, arsenic, tellurium) or a sulfide (germanium). Antimony, first obtained by heating its sulfide, stibnite, was later discovered in native form.

Origin and use of the term

Although a distinction had existed between metals and other mineral substances since ancient times, it was only towards the end of the 18th century that a basic classification of chemical elements as either metallic or nonmetallic substances began to emerge. It would take another nine decades before the term "nonmetal" was widely adopted.

Greek philosopher Aristotle (384–322 BCE) categorized substances found in the earth as either metals or "fossiles".

Around 340 BCE, in Book III of his treatise Meteorology, the ancient Greek philosopher Aristotle categorized substances found within the Earth into metals and "fossiles". The latter category included various minerals such as realgar, ochre, ruddle, sulfur, cinnabar, and other substances that he referred to as "stones which cannot be melted".

Until the Middle Ages the classification of minerals remained largely unchanged, albeit with varying terminology. In the fourteenth century, the English alchemist Richardus Anglicus expanded upon the classification of minerals in his work Correctorium Alchemiae. In this text, he proposed the existence of two primary types of minerals. The first category, which he referred to as "major minerals", included well-known metals such as gold, silver, copper, tin, lead, and iron. The second category, labeled "minor minerals", encompassed substances like salts, atramenta (iron sulfate), alums, vitriol, arsenic, orpiment, sulfur, and similar substances that were not metallic bodies.

The term "nonmetallic" dates back to at least the 16th century. In his 1566 medical treatise, French physician Loys de L'Aunay distinguished substances from plant sources based on whether they originated from metallic or non-metallic soils.

Later, the French chemist Nicolas Lémery discussed metallic and nonmetallic minerals in his work Universal Treatise on Simple Drugs, Arranged Alphabetically published in 1699. In his writings, he contemplated whether the substance "cadmia" belonged to either the first category, akin to cobaltum (cobaltite), or the second category, exemplified by what was then known as calamine—a mixed ore containing zinc carbonate and silicate.

French nobleman and chemist Antoine Lavoisier (1743–1794), with a page of the English translation of his 1789 Traité élémentaire de chimie, listing the elemental gases oxygen, hydrogen and nitrogen (and erroneously including light and caloric); the nonmetallic substances sulfur, phosphorus, and carbon; and the chloride, fluoride and borate ions

The pivotal moment in the systematic classification of chemical elements into metallic and nonmetallic substances came in 1789 with the work of Antoine Lavoisier, a French chemist. He published the first modern list of chemical elements in his revolutionary Traité élémentaire de chimie. The elements were categorized into distinct groups, including gases, metallic substances, nonmetallic substances, and earths (heat-resistant oxides). Lavoisier's work gained widespread recognition and was republished in twenty-three editions across six languages within its first seventeen years, significantly advancing the understanding of chemistry in Europe and America.

The widespread adoption of the term "nonmetal" followed a complex process spanning nearly nine decades. In 1811, the Swedish chemist Berzelius introduced the term "metalloids" to describe nonmetallic elements, noting their ability to form negatively charged ions with oxygen in aqueous solutions. While Berzelius' terminology gained significant acceptance, it later faced criticism from some who found it counterintuitive, misapplied, or even invalid. In 1864, reports indicated that the term "metalloids" was still endorsed by leading authorities, but there were reservations about its appropriateness. The idea of designating elements like arsenic as metalloids had been considered. By as early as 1866, some authors began preferring the term "nonmetal" over "metalloid" to describe nonmetallic elements. In 1875, Kemshead observed that elements were categorized into two groups: non-metals (or metalloids) and metals. He noted that the term "non-metal", despite its compound nature, was more precise and had become universally accepted as the nomenclature of choice.

Suggested distinguishing criteria

Properties suggested
to distinguish metals from nonmetals

Year	Property and type
1743	Heaviness	P
1803	Density and electrical conductivity	P
1821	Opacity	P
1906	Hydrolysis of halides	C
1911	Cation formation	C
1927	Goldhammer-Herzfeld metallization criterion	P
1949	Bulk coordination number	P
1956	Minimum excitation potential	C
1956	Acid-base nature of oxides	C
1957	Electron configuration	A
1962	Sonorousness	P
1966	Physical state	P
1969	Melting and boiling points, electrical conductivity	P
1973	Critical temperature	P
1977	Sulfate formation	C
1977	Oxide solubility in acids	C
1979	3D electrical conductivity	P
1986	Enthalpy of vaporization	P
1991	Liquid range	P
1999	Temperature coefficient of resistivity	P
1999	Element structure (in bulk)	P
2000	Configuration energy	C
2001	Packing efficiency	P
2010	Electrical conductivity at absolute zero	P
2010	Electron band structure	A
2017	Thermal conductivity	P
2017	Atomic conductance	A
2020	Number density and atomic radius	P
Physical/Chemical/Atomic: P/C/A

From the mid-1700s, a variety of physical, chemical, and atomic properties have been suggested for distinguishing metals from nonmetals (or other bodies), as listed in the accompanying table. Some of the earliest recorded properties are the (high) density and (good) electrical conductivity of metals.

In 1809, the British chemist and inventor Humphry Davy made a groundbreaking discovery that reshaped the understanding of metals and nonmetals. When he isolated sodium and potassium, their low densities (floating on water!) contrasted with their metallic appearance, challenging the stereotype of metals as dense substances. Nevertheless, their classification as metals was firmly established by their distinct chemical properties.

One of the most commonly recognized properties used in this context is the temperature coefficient of resistivity, the effect of heating on electrical resistance and conductivity. As temperature rises, the conductivity of metals decreases while that of nonmetals increases. However, plutonium, carbon, arsenic, and antimony defy the norm. When plutonium (a metal) is heated within a temperature range of −175 to +125 °C its conductivity increases. Similarly, despite its common classification as a nonmetal, when carbon (as graphite) is heated it experiences a decrease in electrical conductivity. Arsenic and antimony, which are occasionally classified as nonmetals, show behavior similar to carbon, highlighting the complexity of the distinction between metals and nonmetals.

Kneen and colleagues proposed that the classification of nonmetals can be achieved by establishing a single criterion for metallicity. They acknowledged that various plausible classifications exist and emphasized that while these classifications may differ to some extent, they would generally agree on the categorization of nonmetals.

Emsley pointed out the complexity of this task, asserting that no single property alone can unequivocally assign elements to either the metal or nonmetal category. Furthermore, Jones emphasized that classification systems typically rely on more than two attributes to define distinct types.

Johnson distinguished between metals and nonmetals on the basis of their physical states, electrical conductivity, mechanical properties, and the acid-base nature of their oxides:

1. gaseous elements are nonmetals (hydrogen, nitrogen, oxygen, fluorine, chlorine and the noble gases);
2. liquids (mercury, bromine) are either metallic or nonmetallic: mercury, as a good conductor, is a metal; bromine, with its poor conductivity, is a nonmetal;
3. solids are either ductile and malleable, hard and brittle, or soft and crumbly:

a. ductile and malleable elements are metals;

b. hard and brittle elements include boron, silicon and germanium, which are semiconductors and therefore not metals; and

c. soft and crumbly elements include carbon, phosphorus, sulfur, arsenic, antimony, tellurium and iodine, which have acidic oxides indicative of nonmetallic character.

Density and electronegativity in the periodic table H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po Rn Ra                                                                                                                                                 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Ac Th Pa U Np Pu Am Cm Bk Cf Es Electronegativity (EN): < 1.9 ≥ 1.9 (revised Pauling) Density (D):  < 7 g/cm3  D < 7 and EN ≥ 1.9 for all nonmetallic elements ≥ 7 g/cm3  D ≥ 7 or EN < 1.9 (or both) for all metals

Several authors have noted that nonmetals generally have low densities and high electronegativity. The accompanying table, using a threshold of 7 g/cm³ for density and 1.9 for electronegativity (revised Pauling), shows that all nonmetals have low density and high electronegativity. In contrast, all metals have either high density or low electronegativity (or both). Goldwhite and Spielman added that, "... lighter elements tend to be more electronegative than heavier ones." The average electronegativity for the elements in the table with densities less than 7 gm/cm³ (metals and nonmetals) is 1.97 compared to 1.66 for the metals having densities of more than 7 gm/cm³.

Some authors divide elements into metals, metalloids, and nonmetals, but Oderberg disagrees, arguing that by the principles of categorization, anything not classified as a metal should be considered a nonmetal.

Development of types

Bust of Dupasquier (1793–1848) in the Monument aux Grands Hommes de la Martinière in Lyon, France.

In 1844, Alphonse Dupasquier, a French doctor, pharmacist, and chemist, established a basic taxonomy of nonmetals to aid in their study. He wrote:

They will be divided into four groups or sections, as in the following:

Organogens—oxygen, nitrogen, hydrogen, carbon

Sulphuroids—sulfur, selenium, phosphorus

Chloroides—fluorine, chlorine, bromine, iodine

Boroids—boron, silicon.

Dupasquier's quartet parallels the modern nonmetal types. The organogens and sulphuroids are akin to the unclassified nonmetals. The chloroides were later called halogens. The boroids eventually evolved into the metalloids, with this classification beginning from as early as 1864. The then unknown noble gases were recognized as a distinct nonmetal group after being discovered in the late 1800s.

His taxonomy was noted for its natural basis. That said, it was a significant departure from other contemporary classifications, since it grouped together oxygen, nitrogen, hydrogen, and carbon.

In 1828 and 1859, the French chemist Dumas classified nonmetals as (1) hydrogen; (2) fluorine to iodine; (3) oxygen to sulfur; (4) nitrogen to arsenic; and (5) carbon, boron and silicon, thereby anticipating the vertical groupings of Mendeleev's 1871 periodic table. Dumas' five classes fall into modern groups 1, 17, 16, 15, and 14 to 13 respectively.

Classification of metalloids

Germanium, first thought to be a poorly conducting metal due to the presence of impurities

Boron and silicon were recognized early on as nonmetals but arsenic, antimony, tellurium, and germanium have a more complicated history. While the suitability of arsenic being counted as a metalloid had been considered in 1864, Mendeleev, in 1897, counted it and antimony as metals. Although tellurium likely acquired an "ium" suffix due to its metallic appearance, Mendeleev said it represented a transition between metals and nonmetals. The semiconductor germanium was first regarded as a poorly conducting metal due to the presence of impurities. The understanding of it as a semiconductor, and subsequently as a metalloid, emerged in the 1930s with the development of semiconductor physics.

Since the 1940s, these six elements have been increasingly, but not universally, recognized as metalloids. In 1947, Linus Pauling included a reference to them in his classic and influential textbook General chemistry: An introduction to descriptive chemistry and modern chemical theory. He described boron, silicon, germanium, arsenic, antimony (and polonium) as "elements with intermediate properties." He said they were in the center of his electronegativity scale, with values close to 2. The emergence of the semiconductor industry and solid-state electronics in the 1950s and 1960s highlighted the semiconducting properties of germanium and silicon (and boron and tellurium), reinforcing the idea that metalloids were "in-between" or "half-way" elements. Writing in 1982, Goldsmith observed that, "The newest approach is to emphasize aspects of their physical and/or chemical nature such as electronegativity, crystallinity, overall electronic nature and the role of certain metalloids as semiconductors."

Comparison of selected properties

The two tables in this section list some of the properties of five types of elements (noble gases, halogen nonmetals, unclassified nonmetals, metalloids and, for comparison, metals) based on their most stable forms in ambient conditions.

The aim is to show that most properties display a left-to-right progression in metallic-to-nonmetallic character or average values. Some overlap occurs as outlier elements of each type exhibit less-distinct, hybrid-like, or atypical properties. These overlaps or transitional points, along with horizontal, diagonal, and vertical relationships between the elements, form part of the "great deal of information" summarized by the periodic table.

The dashed lines around the columns for metalloids signify that the treatment of these elements as a distinct type can vary depending on the author, or classification scheme in use.

Physical properties by element type

See also § Physical

Physical properties are listed in loose order of ease of their determination.

Property	Element type
	Metals	Metalloids	Unc. nonmetals	Halogen nonmetals	Noble gases
General physical appearance	lustrous	lustrous	◇ lustrous: carbon, phosphorus, selenium ◇ colored: sulfur ◇ colorless: hydrogen, nitrogen, oxygen	◇ lustrous: iodine ◇ colored: fluorine, chlorine, bromine	colorless
Form and density	solid (Hg liquid)	solid	solid or gas	solid or gas (bromine liquid)	gas
	often high density such as iron, lead, tungsten	low to moderately high density	low density	low density	low density
	some light metals including beryllium, magnesium, aluminium	all lighter than iron	hydrogen, nitrogen lighter than air		helium, neon lighter than air
Elasticity	mostly malleable and ductile	brittle	carbon, phosphorus, sulfur, selenium, brittle	iodine brittle	not applicable
Electrical conductivity	good	◇ moderate: boron, silicon, germanium, tellurium ◇ good: arsenic, antimony	◇ poor: hydrogen, nitrogen, oxygen, sulfur ◇ moderate: phosphorus, selenium ◇ good: carbon	◇ poor: fluorine, chlorine, bromine ◇ moderate: I	poor
Electronic structure	metallic (beryllium, strontium, α-tin, ytterbium, bismuth are semimetals)	semimetal (arsenic, antimony) or semiconductor	◇ semimetal: carbon ◇ semiconductor: phosphorus ◇ insulator: hydrogen, nitrogen, oxygen, sulfur	semiconductor (I) or insulator	insulator

Chemical properties by element type

See also § Chemical

Chemical properties are listed from general characteristics to more specific details.

Property	Element type
	Metals	Metalloids	Unc. nonmetals	Halogen nonmetals	Noble gases
General chemical behavior	◇ strong to weakly metallic ◇ noble metals are relatively inert	weakly nonmetallic	moderately nonmetallic	strongly nonmetallic	◇ inert to nonmetallic ◇ radon shows some cationic behavior
Oxides	basic; some amphoteric or acidic	amphoteric or weakly acidic	acidic or neutral	acidic	metastable XeO3 is acidic; stable XeO4 strongly so
	few glass formers	all glass formers	some glass formers	no glass formers reported	no glass formers reported
	ionic, polymeric, layer, chain, and molecular structures	polymeric in structure	◇ mostly molecular ◇ carbon, phosphorus, sulfur, selenium have 1+ polymeric forms	◇ mostly molecular ◇ iodine has a polymeric form, I2O5	◇ mostly molecular ◇ XeO2 is polymeric
Compounds with metals	alloys or intermetallic compounds	tend to form alloys or intermetallic compounds	◇ salt-like to covalent: hydrogen†, carbon, nitrogen, phosphorus, sulfur, selenium ◇ mainly ionic: oxygen	mainly ionic	simple compounds in ambient conditions not known
Ionization energy (kJ mol−1) ‡	low to high	moderate	moderate to high	high	high to very high
	376 to 1,007	762 to 947	941 to 1,402	1,008 to 1,681	1,037 to 2,372
	average 643	average 833	average 1,152	average 1,270	average 1,589
Electronegativity (Pauling) ‡	low to high	moderate	moderate to high	high	high (radon) to very high
	0.7 to 2.54	1.9 to 2.18	2.19 to 3.44	2.66 to 3.98	ca. 2.43 to 4.7
	average 1.5	average 2.05	average 2.65	average 3.19	average 3.3

† Hydrogen can also form alloy-like hydrides
‡ The labels low, moderate, high, and very high are arbitrarily based on the value spans listed in the table

See also

• CHON (carbon, hydrogen, oxygen, nitrogen)
• List of nonmetal monographs
• Metallization pressure
• Nonmetal (astrophysics)
• Period 1 elements (hydrogen, helium)
• Properties of nonmetals (and metalloids) by group

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External links

• Media related to Nonmetals at Wikimedia Commons