Medieval German miners often mistook cobalt ores for precious metals. Thus, they became ill when they tried to purify them, due to the arsenic gas released in the process. Pure cobalt is hard and shiny, and is added to steel and other alloys to make them stronger. Alloys containing cobalt are used in jet engine blades and in artificial joints, such as hip and knee joints. Cobalt is one of the few elements that can be used to make a permanent magnet. The strongest permanent magnets are made of a strong alloy of cobalt, nickel, and aluminum, called alnico. In addition, a radioactive isotope of cobalt, called cobalt-60, is produced in nuclear reactors. This isotope is widely used to irradiate food, a process by which food is exposed to a small dose of radiation to kill harmful germs. Cobalt can also produce an intense shade of blue. Thus, cobalt blue paints and dyes are formed by reacting aluminum with cobalt oxide.

Summary of properties (Co)

Atomic weight58.933194(4)
Discoverer (year)Brandt, Georg (1735)
Natural formmetallic solid (hexagonal)
Electron configuration[Ar] 3d7 4s2
Melting point (ºC)1495
Boiling point (ºC)2870
Abundance in earth's crust (ppm)25
Isotope (abundance)59Co (100)
Density g/cm38.9
Van der Waals radius (pm)200
Covalent radius (pm)118
Electronegativity (Pauling)1.91
Vaporization enthalpy (kJ/mol)382.40
Enthalpy of fusion (kJ/mol)16.20
Specific heat capacity (J/g·K) at 25ºC and 1 atm0.42
Thermal conductivity (W/cm·K) at 25ºC and 1 atm1.000
Oxidation state+3, +2
Electron affinity (eV)0.66
1st Ionization potential (eV)7.8810

Back to the Periodic Table of the Elements.