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Cobalt (Co)

Cobalt is a chemical element of the periodic table with chemical symbol Co and atomic number 27 with an atomic weight of 58.9332 u and is classed as transition metal and is part of group 9 (cobalt group). Cobalt is solid at room temperature.

Cobalt in the periodic table

Atomic number27
Group9 (Cobalt group)
ClassificationTransition Metal
AppearanceHard lustrous gray metal
Color Gray
Number of protons27 p+
Number of neutrons32 n0
Number of electrons27 e-
From Wikipedia, the free encyclopediaCobalt is a chemical element with symbol Co and atomic number 27. Like nickel, cobalt in the Earth's crust is found only in chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal.

Physical properties

Phase at STPSolid
Density8.9 g/cm3
Atomic weight58.9332 u

Thermal properties

Melting point1768 K
1494.85 °C
2722.73 °F
Boiling point3200 K
2926.85 °C
5300.33 °F
Heat of vaporization373.3 kJ/mol

Atomic properties

Electronegativity (Pauling Scale)1.88
Electron affinity63.898 kJ/mol
Oxidation states−3, −1, 0, +1, +2, +3, +4, +5
(an amphoteric oxide)
Ionization energies
  1. 760.4 kJ/mol
  2. 1648 kJ/mol
  3. 3232 kJ/mol
  4. 4950 kJ/mol
  5. 7670 kJ/mol
  6. 9840 kJ/mol
  7. 12440 kJ/mol
  8. 15230 kJ/mol
  9. 17959 kJ/mol
  10. 26570 kJ/mol
  11. 29400 kJ/mol
  12. 32400 kJ/mol
  13. 36600 kJ/mol
  14. 39700 kJ/mol
  15. 42800 kJ/mol
  16. 49396 kJ/mol
  17. 52737 kJ/mol
  18. 134810 kJ/mol
  19. 145170 kJ/mol
  20. 154700 kJ/mol
  21. 167400 kJ/mol
  22. 178100 kJ/mol
  23. 189300 kJ/mol
  24. 204500 kJ/mol
  25. 214100 kJ/mol
  26. 920870 kJ/mol
  27. 966023 kJ/mol

Electron configuration for cobalt

Electron configuration
Shorthand configuration
[Ar] 3d7 4s2
Electron configuration
Full configuration
1s2 2s2 2p6 3s2 3p6 3d7 4s2
Electron configuration chart
Electrons per shell2, 8, 15, 2
Valence electrons 2 or 9
Valency electrons 2,3
Bohr model
CobaltElectron shell for Cobalt, created by Injosoft ABCo
Figure: Shell diagram of Cobalt (Co) atom.
Orbital Diagram

The history of Cobalt

Discovery and first isolationGeorg Brandt (1735)
Discovery of cobalt
Cobalt has been used to color glass since the Bronze Age. The word cobalt is derived from the German kobalt, from kobold meaning "goblin", a superstitious term used for the ore of cobalt by miners. The first attempts to smelt those ores for copper or silver failed, yielding simply powder (cobalt(II) oxide) instead. Because the primary ores of cobalt always contain arsenic, smelting the ore oxidized the arsenic into the highly toxic and volatile arsenic oxide, adding to the notoriety of the ore. Swedish chemist Georg Brandt (1694–1768) is credited with discovering cobalt circa 1735, showing it to be a previously unknown element, distinct from bismuth and other traditional metals. Brandt called it a new "semi-metal". He showed that compounds of cobalt metal were the source of the blue color in glass, which previously had been attributed to the bismuth found with cobalt. Cobalt became the first metal to be discovered since the pre-historical period. All other known metals (iron, copper, silver, gold, zinc, mercury, tin, lead and bismuth) had no recorded discoverers.


List of unique identifiers for Cobalt in various chemical registry databases
CAS Number7440-48-4
ChemSpider ID94547
EC number231-158-0
PubChem CID Number104730