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GaGa at. wt. 69.72 at. no. 31 m.p. 29.78°C b.p. 2403°C sp. gr. 5.904 (29.6°C) solid sp. gr. 6.095 (29.8°C) liquid valence 2 or 3.
| SHELL | K | L | M | N | O | P | Q |
| SUB SHELL | He | Neon | Argon | Krypton | Xenon | Radon | Eka-radon |
| 1s | 2s 2p | 3s 3p | 3d 4s 4p | 4d 5s 5p | 4f 5d 6s 6p | 5f 6d 7s 7p | |
| Gallium | 1s22s22p63s23p63d104s24p1 | ||||||
| Symbol | 2P½ | ||||||
Gallium was predicted and described by Mendeleev as ekaaluminum, and dis- covered spectroscopically by Lecoq de Boisbaudran in 1875, who in the same year obtained the free metal by electrolysis of a solution of the hydroxide in KOH. Gallium is often found as a trace element in diaspore, sphalerite, germanite, bauxite, and coat Some flue dusts from burning coal have been shown to contain as much as 1.5 % gallium. It is the only metal, except for mercury, cesium, and rubi- dium, which can be liquid near room temperatures; this makes possible its use in high-temperature thermometers. It has one of the longest liquid ranges of any metal and has a low vapor pressure even at high temperatures. There is a strong tendency for gallium to supercool below its freezing point. Therefore seeding may be necessary to initiate solidification. Ultra-pure gallium has a beautiful, silvery appearance and the solid metal exhibits a conchoidal frac B-14 ture similar to glass. The metal expands 3.1 % on s&idifying; therefore, it should not be stored in glass or metal containers as they may break as the metal solidifies. Gallium wets glass or porcelain, and forms a brilliant mirror when it is painted on glass. It has found recent use in doping semiconductors and producing solid-state devices, such as transistors. High-purity gallium is attacked only slowly by mineral acids. Magnesium gallate containing divalent impurities, such as Mn + 2, is finding use in commerical ultraviolet activated powder phosphors. Gallium arsenide is capable of converting electricity directly into coherent light. Gallium readily alloys with most metals, and has been used as a component in low-melting alloys. Its toxicity appears to be of a low order, but should be handled with care until more data are forthcoming. The metal can be supplied in ultra- pure form (99.99999 + %).
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