What is "metalloid"

Metalloid \Met"al*loid\, n. [L. metallum metal + -oid: cf. F. m['e]tallo["i]de.]

1. Formerly, the metallic base of a fixed alkali, or alkaline earth; -- applied by Sir Humphrey Davy to sodium, potassium, and some other metallic substances whose metallic character was supposed to be not well defined.

2. Now, one of several elementary substances which in the free state are unlike metals, and whose compounds possess or produce acid, rather than basic, properties; a nonmetal; as, boron, carbon, phosphorus, nitrogen, oxygen, sulphur, chlorine, bromine, etc., are metalloids.

Metalloid \Met"al*loid\, a.

1. Having the appearance of a metal.

2. (Chem.) Having the properties of a nonmetal; nonmetallic; acid; negative.

a. (cx informal English) Characteristic of the metal music genre. n. 1 (context chemistry English) An element, such as silicon or germanium, intermediate in properties between that of a metal and a nonmetal; especially one that exhibits the external characteristics of a metal, but behaves chemically more as a nonmetal. 2 (context chemistry obsolete English) The metallic base of a fixed alkali, or alkaline earth; applied to sodium, potassium, and some other metallic substances whose metallic character was supposed to be not well defined.

adj. of or being a nonmetallic element that has some of the properties of metal; "arsenic is a metalloid element"

A metalloid is any chemical element which has properties in between those of metals and nonmetals, or that has a mixture of them. There is neither a standard definition of a metalloid nor complete agreement on the elements appropriately classified as such. Despite the lack of specificity, the term remains in use in the literature of chemistry.

The six commonly recognised metalloids are boron, silicon, germanium, arsenic, antimony, and tellurium. Five elements are less frequently so classified: carbon, aluminium, selenium, polonium, and astatine. On a standard periodic table, all eleven are in a diagonal area in the p-block extending from boron at the upper left to astatine at lower right, along the dividing line between metals and nonmetals shown on some periodic tables.

Typical metalloids have a metallic appearance, but they are brittle and only fair conductors of electricity. Chemically, they behave mostly as nonmetals. They can form alloys with metals. Most of their other physical and chemical properties are intermediate in nature. Metalloids are usually too brittle to have any structural uses. They and their compounds are used in alloys, biological agents, catalysts, flame retardants, glasses, optical storage and optoelectronics, pyrotechnics, semiconductors, and electronics.

The electrical properties of silicon and germanium enabled the establishment of the semiconductor industry in the 1950s and the development of solid-state electronics from the early 1960s.

The term metalloid originally referred to nonmetals. Its more recent meaning, as a category of elements with intermediate or hybrid properties, became widespread in 1940–1960. Metalloids sometimes are called semimetals, a practice that has been discouraged, as the term semimetal has a different meaning in physics than in chemistry. In physics it more specifically refers to the electronic band structure of a substance.