Gallium

Gallium, symbol Ga, metallic element that remains in the liquid state over a wider range of temperatures than any other element. Gallium is in group 13 (or IIIa) of the periodic table (see Periodic Law); its atomic number is 31.

Gallium was discovered spectroscopically by the French chemist Paul Émile Lecoq de Boisbaudran in 1875; a year later he isolated the element in its metallic state. The name gallium comes from Gallia, a Latin name for France. Gallium is blue-gray in color as a solid and silvery as a liquid. It is one of the few metals that are liquid near room temperature. It can be supercooled; like water, it expands upon freezing. Gallium melts at 30°C (86°F), boils at about 2204°C (about 3999°F), and has a specific gravity of 5.9; the atomic weight of the element is 69.72.

Gallium occurs in small quantities in some varieties of zinc blende, bauxite, pyrite, magnetite, and kaolin. Gallium resembles aluminum in forming trivalent salts and oxides; it also forms a few monovalent and divalent compounds. The low melting point and high boiling point of the metal are used to advantage in high-temperature thermometers. Certain gallium compounds are excellent semiconductors and have been extensively used in rectifiers, transistors, photoconductors, and laser and maser diodes.