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Chromium (Cr)

Chromium is a chemical element of the periodic table with chemical symbol Cr and atomic number 24 with an atomic weight of 51.9962 u and is classed as transition metal and is part of group 6 (chromium group). Chromium is solid at room temperature.

Chromium in the periodic table

Atomic number24
Group6 (Chromium group)
ClassificationTransition Metal
AppearanceSilvery metallic
Color Silver
Number of protons24 p+
Number of neutrons28 n0
Number of electrons24 e-
From Wikipedia, the free encyclopediaChromium is a chemical element with symbol Cr and atomic number 24. It is the first element in Group 6. It is a steely-gray, lustrous, hard and brittle metal which takes a high polish, resists tarnishing, and has a high melting point.

Physical properties

Phase at STPSolid
Density7.19 g/cm3
Atomic weight51.9962 u

Thermal properties

Melting point2180 K
1906.85 °C
3464.33 °F
Boiling point2944 K
2670.85 °C
4839.53 °F
Heat of vaporization339.5 kJ/mol

Atomic properties

Electronegativity (Pauling Scale)1.66
Electron affinity65.21 kJ/mol
Oxidation states−4, −2, −1, 0, +1, +2, +3, +4, +5, +6
(depending on the oxidation state, an acidic, basic, or amphoteric oxide)
Ionization energies
  1. 652.9 kJ/mol
  2. 1590.6 kJ/mol
  3. 2987 kJ/mol
  4. 4743 kJ/mol
  5. 6702 kJ/mol
  6. 8744.9 kJ/mol
  7. 15455 kJ/mol
  8. 17820 kJ/mol
  9. 20190 kJ/mol
  10. 23580 kJ/mol
  11. 26130 kJ/mol
  12. 28750 kJ/mol
  13. 34230 kJ/mol
  14. 37066 kJ/mol
  15. 97510 kJ/mol
  16. 105800 kJ/mol
  17. 114300 kJ/mol
  18. 125300 kJ/mol
  19. 134700 kJ/mol
  20. 144300 kJ/mol
  21. 157700 kJ/mol
  22. 166090 kJ/mol
  23. 721870 kJ/mol
  24. 761733 kJ/mol

Electron configuration for chromium

Electron configuration
Shorthand configuration
[Ar] 3d5 4s1
Electron configuration
Full configuration
1s2 2s2 2p6 3s2 3p6 3d5 4s1
Electron configuration chart
Electrons per shell2, 8, 13, 1
Valence electrons 6
Valency electrons 2
Bohr model
ChromiumElectron shell for Chromium, created by Injosoft ABCr
Figure: Shell diagram of Chromium (Cr) atom.
Orbital Diagram

The history of Chromium

DiscoveryLouis Nicolas Vauquelin (1794)
First isolationLouis Nicolas Vauquelin (1797)
Discovery of chromium
Chromium minerals as pigments came to the attention of the west in the eighteenth century. On 26 July 1761, Johann Gottlob Lehmann found an orange-red mineral in the Beryozovskoye mines in the Ural Mountains which he named Siberian red lead. In 1770, Peter Simon Pallas visited the same site as Lehmann and found a red lead mineral that was discovered to possess useful properties as a pigment in paints. After Pallas, the use of Siberian red lead as a paint pigment began to develop rapidly throughout the region. Crocoite would be the principal source of chromium in pigments until the discovery of chromite many years later. In 1794, Louis Nicolas Vauquelin received samples of crocoite ore. He produced chromium trioxide (CrO3) by mixing crocoite with hydrochloric acid. In 1797, Vauquelin discovered that he could isolate metallic chromium by heating the oxide in a charcoal oven, for which he is credited as the one who truly discovered the element.


List of unique identifiers for Chromium in various chemical registry databases
CAS Number7440-47-3
ChemSpider ID22412
EC number231-157-5
PubChem CID Number23976