Gallium

Gallium sits below aluminium in group 13, with three outer electrons ([Ar]3d10 4s2 4p1), and nearly all its compounds are in the +3 state. The ten 3d electrons shield the nucleus poorly, so gallium's atom is no larger than aluminium's, and its electrons are held more tightly than the trend would suggest. Solid gallium has an unusual structure built from pairs of atoms, and it melts at just 29.76 °C, yet it does not boil until about 2,400 °C, one of the longest liquid ranges of any element. Like water, it expands when it freezes.

Gallium has no ores of its own and is recovered from the liquors used to refine bauxite into alumina, with China producing about 98 percent of the primary supply. Almost all of it ends up in semiconductors. Gallium arsenide handles the high-frequency signals in mobile phones and powers the solar panels on satellites. Gallium nitride makes blue and white LEDs and increasingly the compact fast chargers for laptops and phones.

Discovery

Dmitri Mendeleev predicted eka-aluminium in 1871, estimating its density and other properties. In 1875 the French chemist Paul-Émile Lecoq de Boisbaudran saw two new violet lines in the spectrum of zinc blende from the Pyrenees, and later that year isolated the metal by electrolysis. He named it after Gallia, the Latin name for France. Some suspected a pun on his own name, since gallus is Latin for coq, rooster, but he denied it.