COBALT

TRANSITION ELEMENT: COBALT GROUP

Atomic number:	27
Group numbers:	9
Period:	4
Electronic configuration:	[Ar] 3d⁷ 4s²
Formal oxidation number:	+2 +3
Electronegativities:	1.88
Atomic radius / pm:	125.3
Relative atomic mass:	58.933 194(4)

Cobalt was discovered by Georg Brandt (DE) in 1739. The origin of the name comes from the German word kobald meaning goblin or evil spirit. It is a hard, ductile, lustrous bluish-grey metal and it's surfaces are stable in air. Cobalt reacts over time with dilute acids and has remarkable magnetic properties. Cobalt occurs in compounds with arsenic and sulfur as in cobaltine (CoAsS) and linneite (Co3S4). Pure cobalt is obtained as a by-product of refining nickel, copper and iron. Cobalt is used in many hard alloys; for magnets, ceramics and special glasses. Radioactive cobalt-60 is used in cancer therapy. The price of 99.9 % pure cobalt pieces is 171.20 € for 500 g.

PHYSICAL PROPERTIES
Density / g dm^-3:	8900	(293 K)
	7670	(m.p.)
Molar volume / cm³mol^-1:	6.62	(293 K)
	7.68	(m.p.)
Electrical resistivity / µΩcm:	6.24	(20 °C)

THERMAL PROPERTIES
Thermal conductivity / W m^-1K^-1:	100
Melting point / °C:	1495
Boiling point / °C:	2927
Heat of fusion / kJ mol^-1:	15.2
Heat of vaporization / kJ mol^-1:	382.4
Heat of atomization / kJ mol^-1:	423.082

IONIZATION ENERGIES
First ionization energy / kJ mol^-1:	760.41
Second ionization energy / kJ mol^-1:	1648.27
Third ionization energy / kJ mol^-1:	3232.28

ABUNDANCE OF ELEMENT
in the atmosphere / ppm:	-
in the Earth's crust / ppm:	29
in the oceans / ppm:	0.0005

CRYSTALLOGRAPHIC DATA
Crystal structure:	face-centered cubic
Unit-cell dimensions / pm:	a=354.41
Space group:	Fm3m

ISOTOPES
Isotope	Relative atomic mass	Mass percent (%)
⁵⁹Co	58.933200(2)	100

REDUCTION POTENTIALS
Balanced half-reaction	E^o / V
Co³⁺ + e^- → Co²⁺	+1.808
Co²⁺ + 2e^- → Co(s)	- 0.277
Co₃O₄(s) + 8H⁺ + 2e^- → 3Co²⁺ + 4H₂O	+2.11
Co₂O₃(s) + 6H⁺ + 2e^- → 2Co²⁺ + 3H₂O	+1.75
Co(OH)₂(s) + 2e^- → Co(s) + 2OH^-	- 0.73
Co(NH₃)₆³⁺ + e^- → Co(NH₃)₆²⁺	+0.1
CoO(OH)(s) + H₂O + e^- → Co(OH)₂(s) + OH^-	+0.17