Chromium is a chemical element in the periodic table that has the symbol Cr and atomic number 24.

Notable characteristics

Chromium is a steel-gray, lustrous, hard metal that takes a high polish, is fusible with difficulty, and is resistant to corrosion and tarnishing.

The most common oxidation states of chromium are +2, +3, and +6, with +3 being the most stable. +4 and +5 are relatively rare. Chromium compounds of oxidation state 6 are powerful oxidants.

History

In 1761, Johann Gottlob Lehmann found an orange-red mineral in the Ural Mountains which he named Siberian red lead. Though misidentified as a lead compound with selenium and iron components, the material was in fact lead chromate (PbCrO4), now known as the mineral crocoite.

In 1770, Peter Simon Pallas visited the same site as Lehmann and found a red "lead" mineral that had very useful properties as a pigment in paints. The use of Siberian red lead as a paint pigment developed rapidly. A bright yellow made from crocoite became a very fashionable color.

In 1797, Nicolas-Louis Vauquelin received samples of crocoite ore. He was able to produce chromium oxide (CrO3) by mixing crocoite with  (An aqueous solution of hydrogen chloride; a strongly corrosive acid) hydrochloric acid. In 1798, Vauquelin discovered that he could isolate metallic chromium by heating the oxide in a charcoal oven. He was also able to detect traces of chromium in precious gems, such as ruby, or emerald.

During the 1800s chromium was primarily used as a component of paints but now the primary use (85%) is for metal alloys, with the remainder used in the chemical industry and refractory and foundry industries.

Chromium was named based on the Greek word "chroma" meaning color, because of the many colorful compounds made from it.

Biological role

Trivalent chromium is an essential trace metal and is required for the proper metabolism of sugar in humans. Chromium deficiencies can affect the potency of insulin in regulating sugar balance. Unlike other essential trace metals, chromium has not been found in a metalloprotein with biological activity. Therefore, the functional basis for the chromium requirement in the diet remains unexplained.