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Gallium                                                                                                         

Standard Sate: solid  at 298 K 

Color: silvery white            

It is the only metal, except for mercury, caesium, and rubidium, 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 vapour pressure even at high temperatures.

(Ga), chemical element, metal of main Group IIIa, or boron group, of
the periodic table. It liquefies just above room temperature.

Gallium was discovered (1875) by Paul-�mile Lecoq de
Boisbaudran, who observed its principal spectral lines while examining
material separated from zinc blende. Soon afterward he isolated the
metal and studied its properties, which coincided with those that
Dmitry Ivanovich Mendeleyev had predicted a few years earlier for
eka-aluminum, the then undiscovered element lying between
aluminum and indium in his periodic table.

Though widely distributed at the Earth's surface, gallium does not
occur free or concentrated in independent minerals, except for gallite,
CuGaS2, rare and economically insignificant. It is extracted as a
by-product from zinc blende, iron pyrites, bauxite, and germanite.

Silvery white and soft enough to be cut with a knife, gallium takes on
a bluish tinge because of superficial oxidation. Unusual for its low
melting point (about 30 C [86 F]), gallium also expands upon
solidification and supercools readily, remaining a liquid at
temperatures as low as 0 C (32 F). Gallium remains in the liquid
phase over a temperature range of about 2,000 C (about 3,600 F)
with a very low vapour pressure up to about 1,500 C (about 2,700
F), the longest useful liquid range of any element. The liquid metal
clings to or wets glass and similar surfaces. The crystal structure of
gallium is orthorhombic. Natural gallium consists of a mixture of
two stable isotopes: gallium-69 (60.4 percent) and gallium-71 (39.6
percent).

Somewhat similar to aluminum chemically, gallium slowly oxidizes in
moist air until a protective film forms, and it becomes passive in cold
nitric acid. Gallium does not react with water at temperatures up to
100 C (212 F) but reacts slowly with hydrochloric and other mineral
acids to give the gallium ion, Ga3+. Gallium is amphoteric, reacting
with sodium and potassium hydroxide solutions to yield a gallate and
hydrogen gas. The halogens attack it vigorously.

In most of its compounds gallium has an oxidation state of +3 and, in
a few, +1. There is no evidence for authentic gallium(II) compounds.
The "dihalides," for example, contain monovalent and trivalent
gallium in a one-to-one ratio. With the main Group V
elements--phosphorus, arsenic, and antimony--gallium forms
compounds that have semiconductor properties. Gallium antimonide,
GaSb, and gallium arsenide, GaAs, are used in electronic devices to
perform such functions as voltage rectification and amplification. The
arsenide and the phosphide, GaP, are electroluminescent; the arsenide
emits infrared light, while the phosphide radiates in the visible
spectrum.

Gallium has been considered as a possible heat-exchange medium in
nuclear reactors, although it has a high neutron cross section.
Radioactive gallium-72 shows some promise in the study of bone
cancer; a compound of this isotope is absorbed by the cancerous
portion of the bone. atomic number 31 atomic weight 69.72 melting
point 29.78 C boiling point 2,403 C specific gravity 5.904 (29.6 C)
valence 3 electronic config. 2-8-18-3 or(Ar)3d104s24p1

"gallium" Encyclop�dia Britannica Online.

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