A silvery-white metallic element of group
IIIA of the period table, resembling
aluminum. It is found as a trace element
in bauxite, pyrite,
sphalerite, and germanite. Gallium has
such a low melting point that it will
enter a molten state if held in the hand and will then remain liquid when
cooled down to 0°C. If, however, a globule of molten gallium is touched
with a fragment of the solid metal, below its melting point, it will immediately
solidify. Gallium is used in lasers, transistor semiconductors,
and high-temperature thermometers.
Chemistry of gallium
Gallium dissolves readily in hydrochloric
acid and in potassium hydroxide with the evolution of hydrogen. It forms
one oxide, Ga2O3, which is insoluble in water, but
soluble in ammonia and potassium hydroxide.
The chloride, nitrate, and sulfide are all very soluble in water; the sulfate
combines with ammonia to form an alum.
Discovery of gallium
Gallium was discovered using spectroscopy by P. E. Lecoq de Boisbaudran
in 1875 in a zinc blende found in the Pyrenees; its name is derived from
Gallia, the Latin name for France. However, its properties and
salts were predicted before its discovery by Dmitri Mendeleyev
based on his Periodic Law. Because it occupied a space immediately below
aluminum according to that law he suggested
the name "eka-aluminium" for it.
|relative atomic mass
| oxidation states
||3, 2, 1
||5.91 g cm-3
Gallium arsenide (GaAs) is a rival material to silicon
for making semiconductor chips. GaAs chips process data faster using less
power than silicon chips, but it is not possible to mass produce them as
reliably. Sometimes known as "three-five" material (because gallium has
a valence of 3 and arsenic
of 5) or a binary semiconductor (being
a compound of two materials).