Nonmetal

This article is about the up to two dozen or so chemical elements. For the limited scope of nonmetals in astronomy, see nonmetal (astrophysics). For nonmetallic substances, see materials science.

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Periodic table excerpt (full table below) showing how often elements are effectively classified as nonmetals:

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  consistently

  sometimes

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Nearby metals have a white background.

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Lack of consensus in the definition of nonmetal causes different authors and sources to categorize different elements in this category.

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† While hydrogen (H) is typically positioned within group 1 of the periodic table, as depicted in the full table below, some representations may place it above fluorine (F) in group 17.
‡ Theory and experimental evidence suggest astatine (At) is a metal; it is treated as such in this article.

A nonmetal is a type of chemical element that, in general, has a low density and high electronegativity (the ability of an atom in a molecule to attract electrons to itself). They encompass a diverse selection of elements, ranging from colorless gases like hydrogen to solid substances with a shiny appearance, such as carbon in its graphite form. Nonmetals are usually poor conductors of heat and electricity. When they exist in solid form, they tend to be brittle or crumbly owing to the limited mobility of their electrons. This stands in contrast to metals, which are known for their efficient electrical conductivity and malleability, often being readily transformed into thin sheets and drawn into wires due to the free movement of their electrons. Additionally, whereas compounds of metals tend to be basic in nature those of nonmetals tend to be acidic.

Within the realm of elemental composition, two nonmetals, namely hydrogen and helium, constitute an overwhelming 99% of the observable ordinary matter in the universe by mass. Moreover, five nonmetallic elements, namely hydrogen, carbon, nitrogen, oxygen, and silicon, constitute the majority of the Earth's crust, atmosphere, oceans and biosphere, underscoring their pivotal role in the composition of the planet.

The unique properties exhibited by nonmetallic elements render them essential for various specialized applications, often complementing the capabilities of metallic elements. Vital to the composition of living organisms are the nonmetals hydrogen, oxygen, carbon, and nitrogen, which constitute a significant portion of their structural makeup. Beyond biology, nonmetallic elements play crucial roles in several industries, including electronics, energy storage, agriculture, and chemical production.

While the term "non-metallic" has roots dating back to as far as 1566, there is no widely agreed precise definition of a nonmetal. This ambiguity arises from the existence of elements that exhibit a marked combination of metallic and nonmetallic attributes. The classification of such borderline cases as nonmetals varies depending on the specific criteria employed for classification. Generally, the number of elements recognized as nonmetals falls within the range of 14 to 23 (or 24), reflecting the fluid nature of this classification.

Definition and applicable elements

Like carbon, arsenic (here sealed in a container to prevent tarnishing) vaporises rather than melts when heated. The vapor is lemon-yellow and smells like garlic. The chemistry of arsenic is predominately nonmetallic in nature.

A nonmetal is a chemical element characterized, in general, by its relatively low density and high electronegativity. More broadly speaking, nonmetals are distinguished by their deficiency in metallic properties, including attributes such as luster or shininess, the ability to be flattened into thin sheets or drawn into wires, efficient thermal and electrical conductivity, and the tendency to produce basic rather than acidic oxides when combined with oxygen. The classification of elements as nonmetals lacks a universally stringent definition, resulting in variations among sources regarding which elements are included within this category. The criteria applied for such categorization hinge upon the specific properties that are deemed most indicative of a nonmetallic or metallic character.

While Steudel, in his 2020 textbook Chemistry of the Non-metals compiled a list of twenty-three chemical elements identified as nonmetals, any such list is open to debate and revision. Among these elements, fourteen are commonly and consistently recognized as nonmetals, encompassing hydrogen, oxygen, nitrogen, and sulfur, as well as the highly reactive halogens: fluorine, chlorine, bromine, and iodine. The noble gases, including helium, neon, argon, krypton, xenon, and radon, are also unequivocally categorized as nonmetals, a classification endorsed by Hawley's Condensed Chemical Dictionary.

A degree of ambiguity surrounds the classification of carbon, phosphorus, and selenium, which have usually been designated as nonmetals, while some other sources have considered them as metalloids. Elements traditionally categorized as metalloids, such as boron; silicon and germanium; arsenic and antimony; and tellurium are sometimes positioned as an intermediary class between metals and nonmetals when the criteria employed for differentiation prove inconclusive. Conversely, these elements may also be classified as nonmetals due to their predominantly nonmetallic nature, characterized by weakly acidic chemistry.

Out of the 118 known chemical elements, approximately 20% fall under the classification of nonmetals. However, the status of a select few elements remains subject to ongoing scrutiny and debate. Astatine, which is the fifth element among the halogens, often garners limited attention due to its extreme rarity and intense radioactivity. That said, both theoretical considerations and experimental evidence have suggested that astatine is a metal. Further contributing to the evolving landscape of elemental classification are the superheavy elements, including copernicium (element 112), flerovium (element 114), and oganesson (element 118). While initial indications point to the possibility of these elements being categorized as nonmetals, their definitive classification has yet to be confirmed.

General properties

Properties noted in this section refer to the elements in their most stable forms in ambient conditions unless otherwise mentioned

Physical

Variety in color and form
of some nonmetallic elements

Boron in its β-rhombohedral phase

Metallic appearance of carbon as graphite

Blue color of liquid oxygen

Pale yellow liquid fluorine in a cryogenic bath

Sulfur as a yellow powder

Liquid bromine at room temperature

Metallic appearance of iodine under white light

Liquefied xenon

Approximately half of nonmetallic elements exist in gaseous states, with the majority of the remainder being lustrous solids. Notably, bromine stands as the singular nonmetal that manifests as a liquid, exhibiting such volatility that it often maintains a layer of vapor above its surface. Among solid nonmetals, sulfur is the sole example characterized by a distinct coloration. The fluid nonmetals are distinguished by their relatively low densities, as well as low melting and boiling points, coupled with a deficiency in their ability to conduct heat and electricity effectively. Solid nonmetals, on the other hand, exhibit low densities, brittleness, limited mechanical and structural strength, and a variable range of electrical conductivity, ranging from poor to moderate.

The varied internal structures and bonding arrangements of the nonmetals explain their differences in form. Those nonmetals that exist as isolated atoms, such as xenon, or as discrete molecules, as seen in oxygen, sulfur, and bromine, typically display low melting and boiling points. Many of them remain in the gaseous state at room temperature, due to the weak London dispersion forces that govern the interactions between their atoms or molecules. Conversely, nonmetals that assemble into large-scale structures, such as chains consisting of up to 1,000 atoms, exemplified by selenium, two-dimensional sheets like carbon in its graphite form, or three-dimensional lattices, as observed in silicon, tend to possess higher melting and boiling points. These nonmetals invariably manifest as solids because the energy required to overcome their stronger covalent bonds is considerably higher. In certain instances, nonmetals positioned closer to the left side of the periodic table or further down a given column may exhibit some weak metallic interactions between their molecules, chains, or layers. This phenomenon aligns with their proximity to metallic elements on the periodic table. Such interactions are discernible in boron, carbon, phosphorus, arsenic, selenium, antimony, tellurium and iodine.

Nonmetallic elements exhibit a wide range of visual characteristics, encompassing shiny appearances, distinct colors, or a lack of color altogether. The lustrous sheen observed in elements such as boron, graphitic carbon, silicon, black phosphorus, germanium, arsenic, selenium, antimony, tellurium, and iodine can be attributed to their structural arrangements, which entail varying degrees of delocalized (free-moving) electrons. These electrons disperse incoming visible light, resulting in the observed metallic shine. On the other hand, colored nonmetals, which include sulfur, fluorine, chlorine, and bromine, possess the ability to selectively absorb certain colors (wavelengths) of light while transmitting others. This selective absorption and transmission lead to the exhibition of distinct colors. For example, chlorine, as noted by Elliot, displays a notable yellow-green hue, which arises from its capacity to absorb a broad range of wavelengths in the violet and blue regions of the electromagnetic spectrum. In the case of colorless nonmetals, namely hydrogen, nitrogen, oxygen, and the noble gases, the binding forces that hold their electrons are sufficiently robust. Consequently, these nonmetals do not undergo any absorption within the visible portion of the electromagnetic spectrum, thereby allowing for the complete transmission of all visible light.

The electrical and thermal conductivities, as well as the brittleness observed in nonmetals, can be attributed to their internal atomic arrangements. In contrast to metals, where the presence of freely moving and evenly distributed electrons facilitates high conductivity and malleability, nonmetals generally exhibit limited electron mobility. Noteworthy electrical and thermal conductivity is observed in a select few nonmetals, namely carbon, arsenic, and antimony. Exceptional thermal conductivity is also evident in boron, silicon, phosphorus, and germanium, with this property resulting from the transmission of thermal energy through vibrational movements within their crystalline lattices. Moderate electrical conductivity is discernible in a broader set of nonmetals, including boron, silicon, phosphorus, germanium, selenium, tellurium, and iodine. Moreover, plasticity—a quality associated with malleability and ductility—is observed in specific nonmetals under unique conditions. Notable instances include exfoliated(expanded) graphite and carbon nanotube wires in carbon, white phosphorus (which remains pliable at room temperature and can be cut with a knife), plastic sulfur, and selenium wires, drawn from the molten state.

The physical differences between metals and nonmetals are a result of both internal and external atomic interactions. Internally, the positive charge stemming from the protons within an atom's nucleus exerts a stabilizing influence, preventing the outer electrons from moving freely. Externally, these same electrons experience attractive forces emanating from the protons in neighboring atoms. When the external forces surpass, or are equivalent to, the internal forces, the outer electrons acquire the ability to move freely between atoms, thus leading to the manifestation of metallic properties. Conversely, when the internal forces predominate, nonmetallic properties are the anticipated outcome.

Allotropes

Main article: Allotropy

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

Some chemistry-based typical
differences between metals and nonmetals

Aspect	Metals	Nonmetals
Electronegativity	Lower than nonmetals, with some exceptions	Relatively high
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; never basic
In aqueous solution	Exist as cations	Exist as anions or oxyanions

Many nonmetallic elements exhibit various allotropic forms, each with its distinct physical properties that may vary between metallic and nonmetallic. For instance, carbon, a versatile nonmetal, can manifest as graphite, diamond, and other forms, with graphite displaying relatively good electrical conductivity, while diamond is transparent and an extremely poor conductor. Carbon further exists in various allotropic structures, including buckminsterfullerene, and amorphous and paracrystalline (mixed amorphous and crystalline) variations. Iodine among the halogen nonmetals, the other unclassified nonmetals, and metalloids all show allotropic variations. Allotropic forms of the noble gases are not known.

Chemical

Nonmetals exhibit distinctive characteristics in their chemical behavior, marked by their comparatively high electronegativity values and a propensity to form acidic compounds. For instance, when nonmetals, including metalloids, react with nitric acid, the resultant products often manifest as either acids themselves or oxides with prevailing acidic properties.

Unlike metals, which typically donate electrons during chemical reactions, nonmetals tend to gain or share electrons. This behavior arises from their pursuit of achieving electron configurations akin to the noble gases, known for their stable outer electron shells. For nonmetals, this electron configuration alignment is succinctly encapsulated by the duet and octet rules, offering heuristics for understanding their electron interactions. Metals, on the other hand, follow a less rigidly predictive 18-electron rule.

Nonmetals also generally exhibit higher ionization energies, electron affinities, and standard reduction potentials compared to metals. In broad terms, an element's nonmetallic character tends to increase in tandem with the elevation of these values, and with electronegativity.

The chemical distinctions between metals and nonmetals primarily arise from the interplay of attractive forces between an atom's positively charged nucleus and its negatively charged outer electrons. In progressing from left to right across each period of the periodic table, the nuclear charge escalates, concurrent with an associated decrease in atomic radius. This phenomenon results from the intensified attraction of the outer electrons toward the nucleus. In the case of metals, the nuclear charge effect is generally less pronounced compared to nonmetallic elements. Consequently, metals tend to lose electrons during bonding, leading to the formation of positively charged or polarized atoms or ions. Conversely, nonmetals, owing to their stronger nuclear charge, have a proclivity to gain those same electrons, thus giving rise to negatively charged ions or polarized atoms.

The number of compounds formed by nonmetals is vast. In a "top 20" table detailing the elements most frequently encountered in a register of 895,501,834 compounds recorded by the Chemical Abstracts Service as of November 2, 2021, nonmetals occupied the first 10 positions. This dominance was underscored by hydrogen, carbon, oxygen, and nitrogen collectively appearing in a majority (80%) of the compounds. Silicon, which falls under the category of metalloids, held the 11th position. The highest-rated metal, iron, accounted for a mere 0.14% of occurrences, placing it in the 12th position. Examples of compounds involving nonmetals include boric acid (H
₃BO
₃), used in ceramic glazes; selenocysteine (C
₃H
₇NO
₂Se), the 21st amino acid of life; phosphorus sesquisulfide (P₄S₃), used in the production of strike anywhere matches; and teflon ((C
₂F
₄)_n), renowned for its application in non-stick coatings for various cookware.

Complications

Periodic table emphasizing the first row of each block. Normally, helium (He), classified as a noble gas, is positioned above neon (Ne) along with other noble gases. In this representation, the elements featured within the scope of this article are enclosed by thick black borders. The status of oganesson (Og, element 118) remains uncertain and is yet to be definitively determined.

This graph displays the electronegativity values of the Group 16 chalcogen elements as they descend down the group within the periodic table. The data reveal a distinctive W-shaped alternation or secondary periodicity pattern in electronegativity. This intriguing trend provides valuable insights into the chemical behavior and properties of these elements.

The chemistry of nonmetals is further complicated by the presence of anomalies observed in the first row of each periodic table block. These anomalies are particularly notable in elements such as hydrogen, boron (which exhibits characteristics of both nonmetals and metalloids), carbon, nitrogen, oxygen, and fluorine. In progressing to later rows, these anomalies evolve into secondary periodic patterns or non-uniform trends within most of the p-block groups. Additionally, in the heavier nonmetals, unusual oxidation states become apparent, further adding to the intricacies of their chemical behavior.

First row anomaly

The first row anomaly, starting with hydrogen, primarily arises from the unique electron configurations exhibited by these elements. Hydrogen, in particular, is renowned for its versatility in forming various types of chemical bonds. Most commonly, it engages in covalent bonding. However, it can also relinquish its single electron when in aqueous solution, resulting in the formation of a naked proton with tremendous polarizing capabilities. This proton readily attaches itself to the lone electron pair of an oxygen atom within a water molecule, thereby serving as a foundation for the principles of acid-base chemistry. Hydrogen atoms within molecules can also establish secondary, albeit weaker, bonds with atoms or groups of atoms in neighboring molecules. As observed by Cressey, these bonds contribute to numerous phenomena, including the hexagonal symmetry of snowflakes, the structural integrity of DNA's double helix, the three-dimensional configuration of proteins, and even the elevation of water's boiling point, facilitating the preparation of a decent cup of tea.

Elements ranging from hydrogen and helium to boron through neon exhibit unusually compact atomic radii. This phenomenon stems from the absence of inner analogues for the 1s and 2p subshells in these elements (that is, there is no zero shell and no 1p subshell). Consequently, they experience minimal electron repulsion effects, in contrast to the 3p, 4p, and 5p subshells found in heavier elements. Ionization energies and electronegativities within this subset of elements are correspondingly higher than anticipated based on periodic trends. The diminutive atomic radii of carbon, nitrogen, and oxygen further facilitate the formation of double or triple bonds in these elements' compounds.

While it would normally be expected for hydrogen and helium to be situated atop the s-block elements, the pronounced first row anomaly associated with these two elements justifies alternative placements. In certain periodic table representations, hydrogen is positioned above fluorine in group 17 rather than over lithium in group 1. Similarly, helium is often situated above neon in group 18 instead of over beryllium in group 2.

Secondary periodicity

A distinct alternation occurs in certain periodic trends upon descending groups 13 to 15 and to a lesser extent in groups 16 to 17. Following the initial row of d-block metals, spanning scandium to zinc, the 3d electrons found in the subsequent p-block elements—namely, gallium (classified as a metal), germanium, arsenic, selenium, and bromine—exhibit a reduced capacity to effectively shield the growing positive nuclear charge. A similar phenomenon becomes evident with the introduction of the fourteen f-block metals located between barium and lutetium. This collective effect gives rise to atomic radii that are smaller than what might be anticipated for elements starting from hafnium (Hf) onward.

Unusual oxidation states

The larger atomic radii observed in the heavier nonmetals within groups 15 to 18 facilitate the attainment of higher bulk coordination numbers and contribute to lower electronegativity values. This characteristic enhances their ability to accommodate higher positive charges, allowing these elements to exhibit oxidation states other than the lowest associated with their respective groups, that is 3, 2, 1, or 0. Notable instances of this phenomenon are evident in compounds like phosphorus pentachloride (PCl₅), sulfur hexafluoride (SF₆), iodine heptafluoride (IF₇), and xenon difluoride (XeF₂).

Types

Periodic table excerpt highlighting the four types of nonmetals. Hydrogen is typically found in group 1, but occasionally placed in group 17.

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† moderately strong oxidizing agents
‡ strong oxidizing agents.

Classification methodologies for nonmetals can encompass a range of approaches, varying from as few as two types to as many as six or seven. For instance, the periodic table employed by Encyclopædia Britannica distinguishes noble gases, halogens, and other nonmetals, while allocating elements commonly identified as metalloids into two types, "other metals" and "other nonmetals". Conversely, the periodic table endorsed by the Royal Society of Chemistry adopts a distinct color scheme for each of its eight primary groups, with nonmetals being distributed across seven of these types.

When examining the periodic table from right to left, three or four distinct types of nonmetals can typically be identified; these include:

• The noble gases, known for their relatively inert chemical behavior.
• A group of highly reactive halogen elements encompassing fluorine, chlorine, bromine, and iodine, commonly referred to as nonmetal halogens. or halogen nonmetals (the term used here) or stable halogens.
• A category of unclassified nonmetals, which comprises elements such as hydrogen, carbon, nitrogen, and oxygen. This group lacks a universally recognized collective name.
• The chemically weak metalloids, which are sometimes classified as nonmetals and at other times considered distinct from nonmetals.

Given the metalloids occupy "frontier territory", where metals meet nonmetals, their treatment can vary among authors and classification schemes. Some consider metalloids as distinct from both metals and nonmetals, while others categorize them as nonmetals or as a subset within the nonmetal classification. In certain cases, specific metalloids, such as arsenic and antimony, are counted as metals due to their resemblances to heavy metals. In this context, metalloids are here categorized as nonmetals in light of their characteristic chemical behavior, and for the sake of comparison.

Apart from the metalloids, there is some degree of ambiguity and overlap among the other types of nonmetals, which is not uncommon in classification systems. Elements like carbon, phosphorus, selenium, and iodine exhibit traits that border on the characteristics of metalloids and display certain metallic properties. Hydrogen also shows some metallic character. Among the noble gases, radon stands out as the most metallic, demonstrating unusual cationic behavior for a nonmetal.

Noble gas

Main article: Noble gas

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

Six nonmetals fall under the category of noble gases namely helium, neon, argon, krypton, xenon, and the radioactive radon. In traditional periodic tables, these elements occupy the far-right column. They are referred to as noble gases due to their distinctive characteristic of exceptionally low chemical reactivity.

Noble gases share several common properties, being colorless, odorless, and nonflammable. Their closed outer electron shells result in feeble interatomic forces of attraction, leading to remarkably low melting and boiling points. Consequently, all noble gases exist in the gaseous state under standard conditions, including those with atomic masses surpassing that of many typically solid elements.

From a chemical perspective, noble gases exhibit relatively high ionization energies, either nil or negative electron affinities, and relatively high to very high electronegativity. The number of compounds formed by noble gases now counts in the hundreds and continues to expand, with the majority involving combinations of oxygen or fluorine with either krypton, xenon, or radon.

In terms of the periodic table, a noteworthy analogy can be drawn between the noble gases and noble metals, such as platinum and gold, due to their shared reluctance to form compounds with other elements. For instance, xenon, when in the +8 oxidation state, gives rise to a pale yellow explosive oxide known as XeO₄. Conversely, osmium, another noble metal, yields a yellow and highly oxidizing oxide, OsO₄. Parallels can also be observed in the chemical formulas of oxyfluorides, such as XeO₂F₄ and OsO₂F₄, and XeO₃F₂ and OsO₃F₂.

The Earth's atmosphere contains approximately 10¹⁵ tonnes of noble gases, with an additional presence of up to 7% helium in natural gas. Radon, a noble gas, emanates from rocks as a byproduct of the natural decay processes of uranium and thorium. Furthermore, it is estimated that the Earth's core may contain around 10¹³ tons of xenon, predominantly in the form of stable XeFe₃ and XeNi₃ intermetallic compounds. This phenomenon may account for the observed depletion of more than 90% of the expected amount of xenon in the Earth's atmosphere through studies of its composition.

Halogen

See also: Halogen

A cluster of purple fluorite CaF
₂, the most common fluorine mineral, between two quartzes. It is the main source of fluorine for commercial uses.

While the halogen nonmetals exhibit pronounced reactivity and corrosiveness, they can also be found in various everyday compounds, such as toothpaste (containing NaF), ordinary table salt (NaCl), swimming pool disinfectants (NaBr), and food supplements (KI). The term 'halogen' derives from the Greek words meaning "salt former."

Physically, fluorine and chlorine present as pale yellow and yellowish-green gases, respectively; bromine is a reddish-brown liquid, typically overlaid by a layer of vaporous fumes; and iodine, under white light, appears as a solid with a metallic sheen. Electrically, the first three elements are insulators, while iodine behaves as a semiconductor along its crystallographic planes.

From a chemical standpoint, halogen nonmetals are characterized by high ionization energies, electron affinities, and electronegativity values, often displaying strong oxidizing properties. This is reflected in their corrosive nature. All four halogens exhibit a propensity to form predominantly ionic compounds with metals, in contrast to the remaining nonmetals, except for oxygen, which tend to form primarily covalent compounds with metals. The halogen nonmetals represent the pinnacle of nonmetallic character, exemplified by their highly reactive and strongly electronegative nature.

In the context of the periodic table, the highly nonmetallic halogens, which belong to Group 17, find their counterparts in the form of the highly reactive alkali metals, including sodium and potassium, situated in Group 1. It is noteworthy that most of the alkali metals, seemingly emulating the halogen nonmetals, are known to form −1 anions, a behavior rarely occurring among metals.

The halogen nonmetals are commonly found in minerals associated with salts. Fluorine, for example, is present in fluorite (CaF₂), a mineral that enjoys widespread occurrence. Chlorine, bromine, and iodine can be found in various brines. Interestingly, a 2012 study reported the discovery of native fluorine (F
₂) by weight in antozonite, constituting approximately 0.04% of its weight. These inclusions were attributed to the effects of radiation emanating from tiny amounts of uranium impurities.

Metalloid

Main article: Metalloid

A crystal of realgar, also known as "ruby sulphur" or "ruby of arsenic", an arsenic sulfide mineral As₄S₄. The two elements involved each have a predominately nonmetallic chemistry.

The category of metalloids encompasses six elements that are commonly recognized as such: boron, silicon, germanium, arsenic, antimony, and tellurium, all of which exhibit a metallic appearance. On the standard periodic table, these elements occupy a diagonal region within the p-block, extending from boron in the upper left to tellurium in the lower right. This region straddles the boundary between metals and nonmetals, as depicted on some periodic tables.

Metalloids are characterized by their brittleness and varying electrical conductivity, ranging from poor to good. Boron, silicon, germanium, and tellurium are known as semiconductors. On the other hand, arsenic and antimony possess electronic structures akin to semimetals, although they also exhibit less stable semiconducting forms.

As to their chemical behavior, metalloids generally display characteristics more in line with chemically weak nonmetals. Within the group of nonmetallic elements, they tend to exhibit the lowest ionization energies, electron affinities, and electronegativity values, and they are relatively modest as oxidizing agents. Additionally, metalloids are inclined to form alloys when combined with metals.

In terms of the periodic table, just to the left of the weakly nonmetallic metalloids, there exists a less clearly defined set of weakly metallic metals. This category includes elements like tin, lead, and bismuth, most often referred to as post-transition metals. Dingle explains the situation as follows:

... 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'.

Metalloids are typically encountered in compounds alongside oxygen, sulfur, or, in the case of tellurium, gold or silver. For example, boron is commonly found in boron-oxygen borate minerals, often present in volcanic spring waters. Silicon is a constituent of silicon-oxygen minerals, such as silica (commonly found in sand). Germanium, arsenic, and antimony are primarily encountered as components of sulfide ores. Tellurium is typically found in telluride minerals that often accompany gold or silver deposits. In some instances, native forms of arsenic, antimony, and tellurium have been reported.

Unclassified

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

After categorizing nonmetallic elements into noble gases, halogens, and metalloids, the remaining seven nonmetals encompass hydrogen, carbon, nitrogen, oxygen, phosphorus, sulfur, and selenium.

Physically, the unclassified nonmetals appear to lack rhyme or reason. In their most stable forms, three of them exist as colorless gases (H, N, O), three exhibit a metallic appearance (C, P, Se), and one presents as yellow (S). Electrically, graphitic carbon behaves as a semimetal within its planes and a semiconductor perpendicular to those planes. Phosphorus and selenium are both semiconductors, while hydrogen, nitrogen, oxygen, and sulfur are insulators.

Continuing the theme, these elements are recognized for their diversity, making it challenging to assign a collective classification. They are often referred to as "other nonmetals" or simply "nonmetals," residing between the metalloids and the halogens.

Consequently, their chemistry is typically taught separately, based on their respective positions within four different groups on the periodic table. For instance: hydrogen in group 1; the group 14 nonmetals, which may include silicon and germanium; the group 15 nonmetals, including nitrogen, phosphorus, and potentially arsenic and antimony; and the group 16 nonmetals, comprising oxygen, sulfur, selenium, and possibly tellurium. There are alternative subdivisions based on individual author preferences.

Hydrogen exhibits a dual nature, displaying characteristics both akin to a metal and those typical of a nonmetal. Resembling a metal, it can readily lose its single electron, substituting for alkali metals in standard alkali metal structures and forming alloy-like hydrides with certain transition metals, characterized by metallic bonding. Conversely, it exists as an insulating diatomic gas, a hallmark of nonmetals, and during chemical reactions, it tends to acquire the electron configuration of helium. This transformation is achieved through the formation of ionic or covalent bonds, or by attaching itself to a lone pair of electrons.

Despite their diversity, the unclassified nonmetals share several common properties. Unlike the highly reactive halogens, most of them occur naturally in the environment. They play significant roles in biological and geochemical processes. While their physical and chemical characteristics lean toward the moderately non-metallic, they all exhibit corrosive tendencies. Hydrogen can corrode metals, carbon can corrosion can occur in fuel cells, dissolved nitrogen or sulfur contributes to acid rain, oxygen causes iron to rust, and white phosphorus, the least stable form, ignites in air, leaving behind phosphoric acid residue. Untreated selenium in soils can produce corrosive hydrogen selenide gas. When combined with metals, the unclassified nonmetals can create exceptionally hard (interstitial or refractory) compounds thanks to their relatively small atomic radii and sufficiently low ionization energies. Additionally, they tend to form bonds with themselves, particularly in solid compounds. Diagonal periodic table relationships on the periodic table among these nonmetals mirror similar relationships found among the metalloids.

In the context of the periodic table, an analogy can be drawn between the unclassified nonmetals and transition metals and a geographic comparison can be made. The unclassified nonmetals are situated between the strongly nonmetallic halogens on the right and the weakly nonmetallic metalloids on the left. In contrast, the transition metals occupy a region between the more reactive metals found on the left side of the periodic table and the less reactive metals on the right, essentially forming a transitional bridge between the two.

Unclassified nonmetals are commonly found in their elemental forms (oxygen, sulfur) or in association with either of these two elements. Examples of their occurrence include:

• Hydrogen is abundant in the Earth's oceans as a component of water and can be found in natural gas, including methane and hydrogen sulfide.
• Carbon is present in various forms, such as carbonates found in limestone, dolomite, and marble. It also occurs as graphite, mainly within metamorphic silicate rocks, resulting from the compression and heating of sedimentary carbon compounds.
• Oxygen is a major constituent of the Earth's atmosphere and is present in oceans as part of water. It can also be found in the Earth's crust in the form of oxide minerals.
• Phosphorus is widely distributed in nature, primarily as phosphorus-oxygen phosphates.
• Elemental sulfur can be discovered near hot springs and volcanic regions across different regions worldwide. Sulfur minerals are also prevalent, commonly existing as sulfides or oxygen-sulfur sulfates.
• Selenium is often encountered in metal sulfide ores, where it can partially replace sulfur. In certain instances, elemental selenium can be found.

Prevalence and access

Abundance

Approximate nonmetal composition
of the Earth and its biomass, by weight

Domain	Main components	Next most abundant
Crust	O 61%, Si 20%	H 2.9%
Atmosphere	N 78%, O 21%	Ar 0.5%
Hydrosphere	O 66.2%, H 33.2%	Cl 0.3%
Biomass	O 63%, C 20%, H 10%	N 3.0%

Hydrogen and helium are recognized as the predominant elements in the universe, collectively constituting an estimated 99% of all ordinary matter. These two elements also comprise over 99.9% of the total number of atoms present. Oxygen follows as the next most abundant element, representing approximately 0.1% of the universe's elemental composition. Less than five per cent of the universe is believed to be made of ordinary matter, represented by stars, planets, and living beings. The balance is hypothesized to be made of dark energy and dark matter, both of which are currently poorly understood.

Five nonmetals—hydrogen, carbon, nitrogen, oxygen, and silicon—play pivotal roles in shaping the Earth's composition. These elements collectively constitute the foundational building blocks of the Earth's crust, atmosphere, hydrosphere, and biomass. Their relative quantities, as outlined in the accompanying table, emphasize their fundamental significance in the terrestrial environment.

Extraction

Germanium occurs in some zinc-copper-lead ore bodies, in quantities sufficient to justify extraction. In 2022, the 99.999% pure form was priced at US$1300 per kilogram.

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

• 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).

Cost

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

Based on the available literature as of April 2023, the cited costs of most nonmetals are less than the $US0.74 per gram cost of silver. The exceptions are boron, phosphorus, germanium, xenon, and radon (notionally):

• Boron costs around $25 per gram for 99.7% pure polycrystalline chunks with a particle size of about 1 cm. Earlier, in 1997, boron was quoted at $280 per gram for polycrystalline 4-to-6-mm-diameter rods of 99.999% purity, about 10 times the then $28.35 per gram cost of gold.
• In 2020, phosphorus in its most-stable black form could "cost up to $1,000 per gram", more than 15 times the cost of gold, whereas ordinary red phosphorus, in 2017, was priced at about $3.40 per kilogram. Researchers hoped to be able to reduce the cost of black phosphorus to as low as $1 per gram.
• Germanium and xenon cost about $1.30 and $7.60 per gram.
• Up to 2013, radon was available from the National Institute of Standards and Technology for $1,636 per 0.2 ml unit of issue, equivalent to about $86,000,000 per gram, with no indication of a discount for bulk quantities.

Uses

A high-voltage circuit-breaker employing sulfur hexafluoride (SF₆) as its inert (air replacement) interrupting medium

The distinctive properties exhibited by nonmetallic elements offer a wide array of applications, often unattainable through the use of metallic elements alone. An impressive facet of nonmetals is their pervasive presence in living organisms, with hydrogen, oxygen, carbon, and nitrogen serving as the elemental building blocks of life itself. Furthermore, these elements have important roles across various industries, ranging from cutting-edge electronics and advanced energy storage systems to the agricultural sector and large-scale chemical production. A few noteworthy examples include:

• Carbon's versatile utility—Carbon fibers, renowned for their exceptional strength-to-weight ratio, find wide-ranging applications in aerospace, automotive manufacturing, and sports equipment development. The remarkable properties of graphene, composed of a single layer of carbon atoms, encompass outstanding electrical and thermal conductivity, rendering it invaluable in electronic devices, energy storage solutions, and the creation of composite materials.
• Nitrogen boosts agriculture—Nitrogen, a fundamental component in fertilizer production, substantially bolsters crop growth and enhances agricultural yields. Its low-temperature attributes render it indispensable for cryogenic applications in preserving biological samples and facilitating food freezing processes.
• Oxygen's vital role—Oxygen, essential for human respiration, plays an indispensable role in life support systems and medical settings where it aids individuals with respiratory difficulties. Moreover, it serves as a critical component in various industrial processes, including metal smelting and waste incineration, due to its combustion-supporting capabilities.
• Silicon empowers electronics—Silicon, the cornerstone of the electronics industry, underpins the manufacture of microchips, solar cells, and an assortment of electronic components. Silicon dioxide (silica) serves as a key material in the production of glass, ceramics, and optical fibers, offering versatile applications in the creation of windows, lenses, and advanced communication networks.
• Sulfur's industrial significance—Sulfur finds extensive utility in the manufacturing of sulfuric acid, a widely used industrial chemical. It also plays a crucial role in the synthesis of various organic compounds. In materials engineering, sulfur compounds are instrumental in the vulcanization process, which enhances the strength and flexibility of rubber-based products.

Shared uses of different subsets of the nonmetals encompass their presence in, or specific uses in the fields of (inert) air replacements; dyestuffs; flame retardants or extinguishers; household accoutrements; lasers and lighting; mineral acids; plug-in hybrid vehicles; and welding gases. To the extent that metalloids show metallic character, they have speciality uses extending to (for example) oxide glasses and alloying components.

History, background, and taxonomy

Discovery

Main article: Discovery of the nonmetals

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 nonmetallic elements were discovered in the 18th and 19th centuries. A handful of nonmetals had already been recognized in antiquity and later periods. Carbon, sulfur, and antimony were among the early nonmetals known to humanity. Arsenic's discovery traces back to the Middle Ages, accredited to the work of Albertus Magnus. A remarkable moment in the history of nonmetal discovery occurred in 1669 when Hennig Brand successfully isolated phosphorus from urine. Curiously, helium, identified in 1868, holds a unique distinction as the only element not initially discovered on Earth itself. Radon emerged as the most recently uncovered nonmetal, its detection marking the close of the 19th century.

The isolation of nonmetallic elements relied on a spectrum of chemical and physical techniques. These methods included spectroscopy, fractional distillation, radiation detection, electrolysis, ore acidification, displacement reactions, combustion and controlled heating processes. Some nonmetals were available in nature as free elements, while others necessitated elaborate processes for extraction:

• Noble gases, those elusive elements characterized by their low reactivity, made their debut through interesting methods. Helium was initially detected via its unique yellow line in the coronal spectrum of the sun. Later, it was observed escaping as bubbles from uranite UO₂ when dissolved in acid. Neon, argon, krypton, and xenon, on the other hand, were procured through the fractional distillation of air. The discovery of radon followed three years after Henri Becquerel's pioneering work on radiation in 1896.
• For the halogen nonmetals, isolation from their halides involved techniques such as electrolysis, acid addition, or displacement. These endeavors were not without risks, as some chemists tragically lost their lives in their pursuit to isolate fluorine.
• The unclassified nonmetals encompassed a variegated history. Carbon occurred naturally in various forms like charcoal, soot, graphite, and diamond. Nitrogen was detected by examining air from which oxygen had been carefully removed. Oxygen itself was obtained through the heating of mercurous oxide. Phosphorus emerged 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 process. Selenium, was first identified as a residue in sulfuric acid.
• Metalloids were typically isolated through the heating of their oxides ((boron, silicon, arsenic, tellurium) or a sulfide (germanium). Antimony, in an unusual twist, was found in its native form and could also be obtained through heating its sulfide compound.

Origin and use of the term

An extract from the English translation of Lavoisier's Traité élémentaire de chimie (1789), listing the elemental gases oxygen, hydrogen and nitrogen (and erroneously including light and caloric), and the nonmetallic substances sulfur, phosphorus, and carbon, and including the chloride, fluoride and borate ions

While a distinction had been made between metals and other mineral substances since ancient times it was only towards the end of the 18th century that a rudimentary classification of chemical elements as either metallic or nonmetallic substances appeared. A further nine decades would pass before the term "nonmetal" was widely adopted.

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

Up to the Middle Ages the situation had remained unchanged aside from the terminology. In the fourteenth century, an English alchemist named Richardus Anglicus elaborated upon the classification of minerals in the text Correctorium Alchemiae. Within this work, he posited the existence of two primary types of minerals. The first, which he termed "major minerals", included well-known metals such as gold, silver, copper, tin, lead, and iron. In contrast, the second category, denoted as "minor minerals", encompassed substances such as salts, atramenta (iron sulfate), alums, vitriol, arsenic, orpiment, sulfur and the like, which are not metallic bodies.

The term "nonmetallic" finds its historical roots tracing back to at least the 16th century. In a 1566 medical treatise, the French physician Loys de L'Aunay wrote of the distinct properties exhibited by substances derived from plant sources. He made a noteworthy comparison between the characteristics of such materials originating from what he termed metallic soils and non-metallic soils.

Later, and more relevantly, the French chemist Nicolas Lémery, in his Universal Treatise on Simple Drugs, Arranged Alphabetically (1699) mentions metallic minerals and nonmetallic minerals. According to him, the substance "cadmia" potentially belonged to either the first category, as with cobaltum (cobaltite), or the second, as exemplified by what used to be referred to as calamine, a mixed ore of zinc carbonate and silicate.

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

The eventual and uniform adoption of the term "nonmetal" underwent a tortuous developmental period of nigh on nine decades. In 1811, Swedish chemist Berzelius introduced the term "metalloids" to describe nonmetallic elements, noting their ability to form negatively charged ions with oxygen in aqueous solution. Although Berzelius' terminology gained widespread acceptance, it later faced criticism. Some commentators viewed it as counterintuitive, misapplied, or even invalid. By 1855, some authors preferred using "nonmetal" over "metalloid" to describe nonmetallic elements. In 1864, it was reported that the term "metalloids" for nonmetals was still endorsed by leading authorities. However, there were reservations about its appropriateness. The idea of instead designating elements like arsenic as metalloids had been contemplated. In an 1875 observation, Kemshead noted that elements were categorized into two groups: non-metals (or metalloids) and metals. He commented that the term "non-metal", despite its compounded nature, was more precise and had since become the universally accepted nomenclature.

Suggested distinguishing criteria

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

Physical Fusibility, malleability and ductility Opacity Goldhammer-Herzfeld criterion for metallization Bulk coordination number Minimum excitation potential Sonorousness Physical state Critical temperature

Enthalpy of vaporization Liquid range Temperature coefficient of resistivity Atomic conductance Packing efficiency 3D electrical conductivity Electrical conductivity at absolute zero Thermal conductivity

Chemical Cation formation Acid-base character of oxides Sulfate formation Oxide solubility in acids Electron related Configuration Structure

In 1809, the British chemist and inventor Humphry Davy made a groundbreaking discovery that revolutionized the understanding of metals and nonmetals. His isolation of sodium and potassium marked a significant departure from the traditional method of distinguishing metals based on their ponderousness or relatively high densities. Sodium and potassium, in contrast, exhibited a remarkable behavior—they floated on water. However, their classification as metals was firmly established by their chemical properties.

As early as 1811, efforts were made to further refine the distinction between metals and nonmetals using various properties. These properties encompassed physical, chemical, and electron-related characteristics. The table provided here enumerates 22 such properties, organized by type and the date of their discovery.

One of the most widely recognized (but unreliable) properties used in this context is the change in electrical conductivity with temperature. Typically, metals exhibit an increase in electrical conductivity as temperature decreases, while nonmetals display the opposite trend. However, certain exceptions challenge this generalization. Plutonium, carbon, arsenic, and antimony, for instance, defy the norm. Plutonium's electrical conductivity increases when heated within a specific temperature range of −175 to +125 °C. Similarly, despite its common classification as a nonmetal, carbon also experiences an increase in electrical conductivity when subjected to heating. Arsenic and antimony, occasionally categorized as nonmetals, exhibit behavior akin to carbon, further underscoring the complexity of the distinction between metals and nonmetals.

Kneen and colleagues proposed that the classification of nonmetals becomes feasible once a singular criterion for metallicity is established. They acknowledged the existence of differing plausible classifications, emphasizing that while these classifications might differ somewhat, they would generally align in their delineation of nonmetals.

However, 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.

Metals and nonmetals sorted by
density and electronegativity (EN)

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

An approach to distinguishing between metallic and nonmetallic properties was suggested by Johnson, emphasizing the significance of physical properties, while acknowledging the potential need for other properties in certain ambiguous cases. His observations highlighted several key distinctions:

1. Physical state—Elements that exist as gases or are nonconductors are typically categorized as nonmetals.
2. Solid nonmetals—Solid nonmetals exhibit characteristics such as hardness and brittleness or softness and crumbliness, setting them apart from metals that are generally malleable and ductile.
3. Chemical behavior—Nonmetal oxides tend to be acidic, providing another useful criterion for identifying nonmetals.

Hein and Arena noted that nonmetals typically possess relatively low densities and high electronegativity, as corroborated by the data in the accompanying table. The nonmetallic elements predominantly occupy the top left quadrant of this table, where both densities and electronegativity values are relatively high. The remaining three quadrants are primarily populated by metals.

While some authors opt for a further subdivision of elements into metals, metalloids, and nonmetals, Oderberg contests this approach and argues that, by the principles of categorization, anything not classified as a metal should be considered a nonmetal.

Development of types

Gaspard Alphonse Dupasquier (1793−1848), French doctor, pharmacist and chemist as depicted in the Monument aux Grands Hommes de la Martinière in Lyon, France. In 1844 he put forward a basic taxonomy of nonmetals.

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

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

Organogens O, N, H, C

Sulphuroids S, Se, P

Chloroides F, Cl, Br, I

Boroids B, Si.

An echo of Dupasquier's fourfold classification is seen in the modern types of nonmetal. The organogens and sulphuroids represent the set of unclassified nonmetals. The chloroide nonmetals came to be independently referred to as halogens. The boroid nonmetals were expanded into the metalloids, starting from as early as 1864. The noble gases, as a discrete grouping, were counted among the nonmetals from as early as 1900.

Comparison

Some properties of various elemental types, including metals, metalloids, unclassified nonmetals, halogen nonmetals, and noble gases, are summarized in the following table. These properties are based on the elements' most stable forms at standard ambient conditions and are presented in a loose order of ease of determination. The chemical properties are listed in a progressive manner, moving from general characteristics to more specific details. The dashed line around the metalloids signifies that, depending on the author or classification scheme, these elements may or may not be recognized as a distinct class or type of elements. Metals are included in this overview as a reference point.

The properties exhibited by these elemental groups generally exhibit a left-to-right progression in terms of metallic-to-nonmetallic character or average values. This arrangement effectively divides the periodic table into metals and nonmetals, revealing varying degrees of gradation within the nonmetallic elements.

The periodic table provides a valuable framework for understanding these distinctions, offering insights into the multifarious nature of elements and their placement within the metallic to nonmetallic spectrum.

Some cross-type properties

Physical property	Metals alkali, alkaline earth, lanthanide, actinide, transition, post-transition	Metalloids boron, silicon, germanium, arsenic, antimony, tellurium	Unclassified nonmetals hydrogen, carbon, nitrogen, phosphorus, oxygen, sulfur, selenium	Halogen nonmetals fluorine, chlorine, bromine, iodine	Noble gases helium, neon, argon, krypton, xenon, radon
Form and heft	◇ solid ◇ often high density such as Fe, Pb, W ◇ some light metals including Be, Mg, Al	◇ solid ◇ low to moderately high density ◇ all lighter than Fe	◇ solid or gas ◇ low density ◇ H, N lighter than air	◇ solid, liquid or gas ◇ low density	◇ gas ◇ low density ◇ He, Ne lighter than air
Appearance	lustrous	lustrous	◇ lustrous: C, P, Se ◇ colorless: H, N, O ◇ colored: S	◇ colored: F, Cl, Br ◇ lustrous: I	colorless
Elasticity	mostly malleable and ductile (Hg is liquid)	brittle	C, black P, S, Se brittle; all four have less stable non-brittle forms	iodine is brittle	not applicable
Electrical conductivity	good	◇ moderate: B, Si, Ge, Te ◇ good: As, Sb	◇ poor: H, N, O, S ◇ moderate: P, Se ◇ good: C	◇ poor: F, Cl, Br ◇ moderate: I	poor
Electronic structure	metallic (Bi is a semimetal)	semimetal (As, Sb) or semiconductor	◇ semimetal: C ◇ semiconductor: P, Se ◇ insulator: H, N, O, S	semiconductor (I) or insulator	insulator
Chemical property	Metals alkali, alkaline earth, lanthanide, actinide, transition, post-transition	Metalloids boron, silicon, germanium, arsenic, antimony, tellurium	Unclassified nonmetals hydrogen, carbon, nitrogen, phosphorus, oxygen, sulfur, selenium	Halogen nonmetals fluorine, chlorine, bromine, iodine	Noble gases helium, neon, argon, krypton, xenon, radon
General chemical behavior	◇ strong to weakly metallic ◇ noble metals are disinclined to react	weakly nonmetallic	moderately nonmetallic	strongly nonmetallic	◇ inert to nonmetallic ◇ Rn shows some cationic behavior
Oxides	◇ basic; some amphoteric or acidic ◇ V; Mo, W; Al, In, Tl; Sn, Pb; Bi are glass formers ◇ ionic, polymeric, layer, chain, and molecular structures	◇ amphoteric or weakly acidic ◇ B, Si, Ge, As, Sb, Te are glass formers ◇ polymeric in structure	◇ acidic (NO 2, N 2O 5, SO 3, SeO 3 strongly so) or neutral (H2O, CO, NO, N2O) ◇ P, S, Se are glass formers; CO2 forms a glass at 40 GPa ◇ mostly molecular ◇ C, P, S, Se have at least one polymeric form	◇ acidic; ClO 2, Cl 2O 7, I 2O 5 strongly so ◇ no glass formers reported ◇ molecular ◇ iodine has at least one polymeric form, I2O5	◇ metastable XeO3 is acidic; stable XeO4 strongly so ◇ no glass formers reported ◇ molecular ◇ XeO2 is polymeric
Compounds with metals	alloys or intermetallic compounds	tend to form alloys or intermetallic compounds	◇ salt-like to covalent: H†, C, N, P, S, Se ◇ mainly ionic: O	mainly ionic	simple compounds in ambient conditions not known
Ionization energy (kJ mol−1)‡	◇ 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)‡	◇ low to high ◇ 0.7 to 2.54 ◇ average 1.5	◇ moderately high ◇ 1.9 to 2.18 ◇ average 2.05	◇ moderately high to high ◇ 2.19 to 3.44 ◇ average 2.65	◇ high ◇ 2.66 to 3.98 ◇ average 3.19	◇ high (Rn) to very high ◇ ca. 2.43 to 4.7 ◇ average 3.3
† Hydrogen can also form alloy-like hydrides ‡ 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)
• Nonmetal (physics)
• 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