A metalloid is a chemical element that has properties in between those of metals and nonmetals. There is no standard definition of a metalloid, nor is there agreement as to which elements are appropriately classified as such. Despite this uncertainty, the term remains in use in chemistry literature. The six commonly recognised metalloids are boron, silicon, germanium, arsenic, antimony and tellurium (pictured). Elements less commonly recognised as metalloids include carbon, aluminium, selenium, polonium and astatine. Typical metalloids have a metallic appearance but are brittle and only fair conductors of electricity. Chemically, they mostly behave as weak nonmetals. They can form alloys with metals. Most of their other properties are intermediate in nature. Metalloids and their compounds are used in alloys, biological agents, flame retardants, glasses, optical storage and optoelectronics, pyrotechnics, semiconductors and electronics. The term metalloid originally referred to nonmetals. Its more recent meaning, as a category of elements with intermediate properties, became widespread in 1940–1960. Metalloids are sometimes called semimetals, a practice that has been discouraged. (Full article...)
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