All practice pages/Interatomic theory/Elements
Element 31, a post-transition metal
A metal that melts in your hand, predicted by Mendeleev before it was found, and a key ingredient of the blue LED.
Period 4, group 13. The other post-transition metals are tinted, and every cell opens its own article.
Three valence electrons, which gallium gives up to form Ga³⁺. With arsenic and nitrogen it forms the covalent semiconductors gallium arsenide and gallium nitride.
Never mined for itself. It is recovered in small amounts while bauxite is processed into aluminum and while zinc ores are refined, and China produces nearly all of it.
Paul-Émile Lecoq de Boisbaudran spotted two new violet lines in the spectrum of a zinc ore in 1875 and isolated the metal the same year. It matched Mendeleev's predicted eka-aluminium so closely, down to its density once it was remeasured, that the periodic table won wide acceptance. He named it after Gallia, Latin for France; some suspected a pun on his own name, since gallus means rooster, le coq in French.
Almost all goes into semiconductors: gallium arsenide chips in phones and in solar cells for satellites, and gallium nitride in blue and white LEDs, laser diodes and compact phone chargers. Galinstan, a gallium-indium-tin alloy that is liquid at room temperature, replaces mercury in some thermometers.
Not very toxic, but liquid gallium attacks aluminum and makes it brittle, so it is kept away from aluminum parts.