Gallium - Ga, 31

Gallium has a melting point of 29.78°C, boiling point of 2403°C, specific gravity of 5.904 (29.6°C), specific gravity of 6.095 (29.8°C, liguid), with a valence of 2 or 3. Gallium has one of the longest liquid temperature ranges of any metal, with a low vapor pressure even at high temperatures. The element has a strong tendency to supercool below its freezing point. Seeding is sometimes necessary to initiate solidification. Pure gallium metal has a silvery appearance. It exhibits a conchoidal fracture that it similar to a glass fracture in appearance. Gallium expands 3.1% on solidifying, so it should not be stored in a metal or glass container that can break upon its solidification. Gallium wets glass and porcelain, forming a brilliant mirror finish on glass. Highly pure gallium is only slowly attacked by mineral acids. Gallium is associated with a relatively low toxicity, but should be handled with care until more health data has been accumulated.

Since it is a liquid near room temperature, gallium is used for high-temperature thermometers. Gallium is used to dope semiconductors and for producing solid-state devices. Gallium arsenide is used to convert electricity into coherent light. Magnesium gallate with divalent impurities (e.g., Mn2+) is used to make commercial ultraviolet-activated powder phosphors.