Chromium

Atomic Number:24Atomic Radius:189 pm (Van der Waals)
Atomic Symbol:CrMelting Point:1907 °C
Atomic Weight:52.00Boiling Point:2671 °C
Electron Configuration:[Ar]3d54s1Oxidation States:6, 5, 4, 3, 2, 1, −1, −2, −4 ​(depending on the oxidation state, an acidic, basic, or amphoteric oxide)

History

From the Greek word chroma, color. Chromium is a steel-gray, lustrous, hard metal that takes a high polish. Discovered in 1797 by the Frenchman Louis Nicolas Vauquelin.

Sources

The principal ore is chromite, which is found in Zimbabwe, Russia, New Zealand, 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, manufacture stainless steel, and form many useful alloys. It is mostly 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 uses chromite 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 chromates are those of sodium and potassium, 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.