Gallium, << GAL ee uhm, >> is a soft, silver-white metal found throughout Earth’s crust. Its general properties resemble those of aluminum. Intermetallic compounds (compounds of two or more metals) with gallium are used as high-temperature rectifiers; as semiconductors in transistors, light-emitting diodes, and semiconductor lasers; and in memory devices in high-speed computers. Gallium remains in liquid form over a larger temperature range than does any other element. It was first used to fill high-temperature thermometers. A mixture of tin, silver, and gallium is used in dental fillings. Gallium is found in various ores, rocks, and minerals, such as diaspore, sphalerite, germanite, bauxite, and coal.
Gallium has the chemical symbol Ga. Its atomic number (number of protons in its nucleus) is 31. Its relative atomic mass is 69.723. An element’s relative atomic mass equals its mass (amount of matter) divided by 1/12 of the mass of carbon 12, the most abundant form of carbon. Gallium boils at 2403 °C and melts at 29.78 °C. Gallium has a density of 5.907 grams per cubic centimeter at 20 °C. Chemists classify gallium as an other metal . For information on the position of gallium on the periodic table, see the article Periodic table .
The French chemist Paul Emile Lecoq de Boisbaudran discovered gallium in 1875.
