nonmetal

 

chemical element possessing certain properties by which it is distinguished from a metal. In general, this distinction is drawn on the basis that a nonmetal tends to accept electrons and form negative ions and that its oxide is acidic. Nonmetals are poor conductors of heat and electricity (see conduction) and do not have the luster of metals. Arsenic, antimony, selenium, and tellurium exhibit both nonmetallic and metallic properties and are called metalloids. Unlike the metals, which are all solids (with the exception of mercury) under ordinary conditions of temperature and pressure, the nonmetals appear in all three states. Argon, chlorine, fluorine, helium, hydrogen, krypton, neon, nitrogen, oxygen, and xenon are normally gases. Bromine is a liquid. Boron, carbon, iodine, phosphorus, silicon, and sulfur are solids. Certain of them, e.g., boron, carbon, iodine, silicon, and sulfur, form crystals, as do the metals. In hardness they vary considerably. Carbon in its allotropic form, the diamond, is the hardest element known. With the exception of carbon, sulfur, nitrogen, oxygen, and the inert gases—argon, helium, krypton, neon, and xenon—the nonmetals do not occur uncombined in nature, but exist in numerous relatively abundant compounds, among which are the oxides, halides (binary halogen compounds), sulfides, carbonates, nitrates, phosphates, silicates, and sulfates. With a few exceptions, the nonmetallic elements are important chiefly for their compounds. For the properties and uses of specific nonmetals, see the separate articles on these elements.

Nonmetal is a term used in chemistry when classifying the chemical elements. On the basis of their general physical and chemical properties, every element in the periodic table can be termed either a metal or a non-metal. (A few elements with intermediate properties are referred to as metalloids.)

The elements generally regarded as nonmetals are:

• hydrogen (H)
• In Group 14: carbon (C)
• In Group 15 (the pnictogens): nitrogen (N), phosphorus (P)
• Several elements in Group 16, the chalcogens: oxygen (O), sulfur (S), selenium (Se)
• All elements in Group 17 - the halogens
• All elements in Group 18 - the noble gases

There is no rigorous definition for the term "nonmetal" - it covers a general spectrum of behaviour. Common properties considered characteristic of a nonmetal include:

• poor conductors of heat and electricity when compared to metals
• they form acidic oxides (whereas metals generally form basic oxides)
• in solid form, they are dull and brittle, rather than metals which are lustrous, ductile or malleable
• usually have lower densities than metals
• they have significantly lower melting points and boiling points than metals
• non-metals have high electronegativity
• nonmetals usually have little or no luster

Only eighteen elements in the periodic table are generally considered nonmetals, compared to over eighty metals, but nonmetals make up most of the crust, atmosphere and oceans of the earth. Bulk tissues of living organisms are composed almost entirely of nonmetals. Many nonmetals (hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, and iodine) are diatomic, and most of the rest are polyatomic.

Periodic tables
Layouts	Standard · Vertical · Full names · Names and atomic masses · Text for last · Huge table · Metals and nonmetals · Blocks · Valences · Inline f-block · 218 elements · Electron configurations · Atomic masses · Electronegativities · Alternatives
Lists of elements	Name · Atomic symbol · Atomic number · Boiling point · Melting point · Density · Atomic mass
Groups	1 ·  2 ·  3 ·  4 ·  5 ·  6 ·  7 ·  8 ·  9 ·  10 ·  11 ·  12 ·  13 ·  14 ·  15 ·  16 ·  17 ·  18
Periods:	1 ·  2 ·  3 ·  4 ·  5 ·  6 ·  7 ·  8
Series	Alkalis ·  Alkaline earths ·  Lanthanides ·  Actinides ·  Transition metals · Poor metals ·  Metalloids ·  Nonmetals ·  Halogens ·  Noble gases
Blocks	s-block ·  p-block ·  d-block ·  f-block ·  g-block

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