Key information
Atomic number: 
24
Atomic weight: 
52
Density: 
7190 kg/m³
Boiling point: 
2938.16° K
Melting point: 
2148.16° K
Heat vapour: 
305.57 kJ/mol
Heat fusion: 
13.82 kJ/mol
Thermal conductivity: 
7.8 W/m/K
Specific heat capacity: 
67 J/kg/K

Chromium has three common oxidation states: +2, +3 and +6 with varying colours.

In 1761, Johann Gottlob Lehmann (1719-1767) found an orange-red mineral in the Ural Mountains which he named Siberian red lead. In 1797, Louis Nicholas Vauquelin, isolated natural lead (II) chromate (PbCrO4) while investigating the mineral. He was able to produce chromium oxide (also chromium trioxide), a red crystalline compound with the chemical formula of CrO3, by mixing the ore with hydrochloric acid. To prepare CrO3 commercially sulphuric acid is added to concentrated solutions of a dichromate salt:

K2Cr2O7 (aq) + 2H2SO4 (l) -> 2KHSO4 (aq) + CrO3 (s) + H2O (aq)

Investigations revealed a new metal within the mineral. As the compounds of the metal tend to be strong coloured Vauquelin proposed the name chrome from the Greek word for colour, a reference to the many brightly coloured compounds of chromium. In 1809 Vauquelin attempted to determine the best conditions for making lead chromate. He obtained it by ionic precipitation using solutions of a lead salt and a chromate. Through his series of experiments, Vauquelin was able to determine that through co-precipitation from solution with lead sulphate the colour could be adjusted, and that the colour could also be varied by changing the temperature of the synthesis which affects the size of the grain.

Electron Shell: 
Amazon Books
Image of The Last Sorcerers: The Path from Alchemy to the Periodic Table
Author: National Academy of Sciences, Richard Morris
Publisher: Henry (Joseph) Press (2003)
Binding: Hardcover, 294 pages