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Concept
Nonmetal (chemistry)
Summary
A nonmetal is a chemical element that, in the broadest sense of the term, has a relatively low density and high electronegativity; they range from colorless gases (like hydrogen) to shiny solids (like carbon, as graphite). They are usually poor conductors of heat and electricity, and brittle or crumbly when solid due to their electrons having low mobility. In contrast, metals are good conductors and most are easily flattened into sheets and drawn into wires since their electrons are generally free-moving. Nonmetal atoms tend to attract electrons in chemical reactions and to form acidic compounds.
Two nonmetals, hydrogen and helium, make up about 99% of ordinary matter in the observable universe by mass. Five nonmetallic elements, hydrogen, carbon, nitrogen, oxygen and silicon, make up most of the Earth's crust, atmosphere, oceans and biosphere.
The distinctive properties of nonmetallic elements allow for specific applications that often cannot be fulfilled by metallic elements alone. Living organisms are composed almost entirely of the nonmetals hydrogen, oxygen, carbon, and nitrogen. Nonmetallic elements are important to industries ranging from electronics and energy storage to agriculture and chemical production.
While the term non-metallic dates from as far back as 1566, there is no widely agreed precise definition of a nonmetal. Some elements have a marked mixture of metallic and nonmetallic properties, and which of these borderline cases are counted as nonmetals varies depending on the classification criteria used. Generally, from 14 to 23 elements are recognized as nonmetals.
A nonmetal is a chemical element that, in the broadest sense of the term, has a relatively low density and high electronegativity. More generally they are deemed to lack a preponderance of metallic properties such as: luster or shininess; the capacity to be flattened into a sheet or drawn into a wire; good thermal and electrical conductivity; and the capacity to form a basic (rather than acidic) oxide.
Official source
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