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Atomic Number: 24
Atomic Symbol: Cr
Atomic Weight: 51.996
Electron Configuration: [Ar]4s13d5
History
(Gr. chroma, color) Discovered in 1797 by Vauquelin, who prepared the
metal the next year, chromium is a steel-gray, lustrous, hard metal that takes a
high polish.
Sources
The principal ore is chromite, which is found in Zimbabwe, Russia,
Transvaal, Turkey, Iran, Albania, Finland, Democratic Republic of Madagascar,
and the Phillippines. The metal is usually produced by reducing the oxide with
aluminum.
Uses
Chromium is used to harden steel, to manufacture stainless steel, and
to form many useful alloys. Much is used in plating to produce a hard, beautiful
surface and to prevent corrosion. Chromium gives glass an emerald green color
and is widely used as a catalyst.
The refractory industry has found chromite useful for forming
bricks and shapes, as it has a high melting point, moderate thermal expansion,
and stability of crystalline structure.
Compounds
All compounds of chromium are colored; the most important are the
chromates of sodium and
potassium and the dichromates and the potassium
and ammonium chrome alums. The dichromates are used as oxidizing agents
in quantitative analysis, also in tanning leather.
Other compounds are of industrial value; lead chromate is chrome
yellow, a valued pigment. Chromium compounds are used in the textile industry as
mordants, and by the aircraft and other industries for anodizing aluminum.
Handling
Chromium compounds are toxic and should be handled with proper
safeguards.
Sources: CRC Handbook of Chemistry and
Physics and the American Chemical Society.
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