A nonmetal is a chemical element that mostly lacks metallic properties. Seventeen elements are generally considered nonmetals, though some authors recognize more or fewer depending on the properties considered most representative of metallic or nonmetallic character. Some borderline elements further complicate the situation.
Nonmetals tend to have low density and high electronegativity (the ability of an atom in a molecule to attract electrons to itself). They range from colorless gases like hydrogen to shiny solids like the graphite form of carbon. Nonmetals are often poor conductors of heat and electricity, and when solid tend to be brittle or crumbly. In contrast, metals are good conductors and most are pliable. While compounds of metals tend to be basic, those of nonmetals tend to be acidic.
The two lightest nonmetals, hydrogen and helium, together make up about 98% of the observable ordinary matter in the universe by mass. Five nonmetallic elements—hydrogen, carbon, nitrogen, oxygen, and silicon—make up the overwhelming majority of the Earth's crust, atmosphere, oceans and biosphere.
The distinct properties of nonmetallic elements allow for specific uses that metals often cannot achieve. Elements like hydrogen, oxygen, carbon, and nitrogen are essential building blocks for life itself. Moreover, nonmetallic elements are integral to industries such as electronics, energy storage, agriculture, and chemical production.
Most nonmetallic elements were not identified until the 18th and 19th centuries. While a distinction between metals and other minerals had existed since antiquity, a basic classification of chemical elements as metallic or nonmetallic emerged only in the late 18th century. Since then nigh on two dozen properties have been suggested as single criteria for distinguishing nonmetals from metals.
Definition and applicable elements
Properties mentioned hereafter refer to the elements in their most stable forms in ambient conditions unless otherwise mentioned
Nonmetal chemical element generally have low density and high electronegativity. They lack most or all of the properties commonly associated with metals: shininess; malleability and ductility; good thermal and electrical conductivity; and a capacity to (mostly) produce basic oxides when combined with oxygen.
There is no precise definition of a nonmetal; any list of such is open to debate and revision. Which elements are included depends on the properties regarded as most representative of nonmetallic or metallic character.
These fourteen elements are effectively always recognized as nonmetals:
{ | class="wikitable" |- | Hydrogen, Nitrogen, Oxygen, Sulfur |- | Fluorine, Chlorine, Bromine, Iodine |- | Helium, Neon, Argon, Krypton, Xenon, Radon |}
Three more are commonly called nonmetals, but some sources list them as metalloids: { | class="wikitable" |- | Carbon, Phosphorus, Selenium |}
The six elements most commonly recognized as metalloids, which are typically seen as intermediates between metals and nonmetals, are here counted as a type of nonmetal due to their relatively low densities and predominantly nonmetallic chemistry, and for comparative purposes: { | class="wikitable" |- | Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium |}
Of the 118 known elements, roughly 20% are classified as nonmetals. Opinions differ as to the status of astatine. Its rarity and extreme radioactivity has resulted in it being frequently ignored in the literature. A comprehensive understanding of its properties is lacking and its classification remains uncertain. As a halogen it has usually been presumed to be a nonmetal. Chemically, studies on trace quantities of astatine, which are not necessarily reliable, have demonstrated characteristics of both metals and nonmetals. Alternatively, given the near-metallic character of its lighter congener iodine, a succession of authors have speculated or presumed astatine would be a metal. A 2013 study based on relativistic chemistry concluded that it would be a monatomic metal with a close-packed crystalline structure, although this has not been experimentally verified. Astatine is precluded from further consideration in this article due to uncertainty as to its behavior and status. The superheavy elements copernicium (element 112), flerovium (114), and oganesson (118) may or may not turn out to be nonmetals; their status has not been confirmed.