Gallium

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MELTING POINT: 29.78°C
BOILING POINT: 2,250°C
DENSITY: 5.907 g/cm ³
MOST COMMON IONS: Ga ²⁺ , Ga ³⁺

In 1870 Dimitri Mendeleev predicted many of the properties of an unknown element that he called eka-aluminum. The element was discovered in 1875 by Paul-Émile Lecoq de Boisbaudran who named it gallium from Gaul, the Latin name for France. The properties of the new element were those predicted by Mendeleev and helped to validate his Periodic Table of the elements.

Gallium can be obtained as a by-product of zinc and alumina production. The metal has an unusually low melting point but a very high boiling point. The liquid range is the largest known for any element, allowing gallium to be used in high-temperature thermometers. The liquid metal has a number of unusual properties: It has a tendency to supercool; to expand on crystallization ; and does not crystallize in any of the common closely packed or body-centered cubic structures.

The chemistry of gallium is very similar to that of aluminum, its congener . Compounds of gallium almost always have a +3 oxidation state. While a few compounds with a +1 and +2 state have been postulated, these are controversial.

One of the most important uses of gallium is in electronic devices, usually in the form of gallium arsenide, which, together with other group-3 or group-5 elements, converts electrical energy to light, and is the basis of the light-emitting diode.

Metallic gallium and its salts have little or no toxicity, compared to the very toxic thallium salts. The toxicity of the aluminum ion is controversial. The gallium ion has been investigated as a possible antitumor agent, but no clinically useful compounds have been produced.

SEE ALSO Inorganic Chemistry ; Mendeleev, Dimitri ; Semiconductors .

Gus J. Palenik

Bibliography

Emsley, John (2001). Nature's Building Blocks: An A–Z Guide to the Elements. New York: Oxford University Press.

Krebs, Robert E. (1998). The History and Use of Our Earth's Chemical Elements: A Reference Guide. Westport, CT: Greenwood Press.

Weeks, Mary E., and Leicester, Henry M. (1968). "Discovery of the Elements." In Journal of Chemical Education, 7th edition. Easton, PA: Journal of Chemical Education.