* Chromium is a member of the transition metals family:
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CHROMIUM / Cr / 24
A hard silvery-bluish metal, with good resistance to corrosion.
The name is derived from the Greek "chroma (color)", and many gems
owe their colors to traces of chromium. Four isotopes are found in
nature:
Cr<52/24> / 84%
Cr<53/24> / 9.5%
Cr<50/24> / 4%
Cr<54/24> / 2.5%
All are stable.
atomic weight: 51.9961
abundance: 21st
density: 7.2 gm/cc
melting point: 1,860 C
boiling point: 2,672 C
valence: 2 <3> 4 6
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The "Cr+++" ion was once referred to as the "chromic" ion, but now is referred to as "chromium(III)". The "CrO4--" ion is referred to as the "chromate" ion.
Chromium is produced at a level of tens of thousands of tonnes a year, mostly for plating -- not just of metal objects, but even those made of plastic -- and for alloying with steel to form stainless steel. It is also used in a range of catalysts. It has a few other minor uses, for example for use in the tanning of leather so that it resists water, but this process produces a polluting effluent and so other processes are being investigated. Chromium is essential to body chemistry, though the quantities needed are so small that people almost never suffer from a chromium deficiency.
