Cobalt

Cobalt, ₂₇Co
General properties
Pronunciation	/ˈkoʊbɒlt/ ( listen)
Appearance	hard lustrous bluish gray metal
Standard atomic weight (Ar, standard)	58.933194(4)
Cobalt in the periodic table
	iron ← cobalt → nickel
Atomic number (Z)	27
Group	group 9
Period	period 4
Element category	transition metal
Block	d-block
Electron configuration	[Ar] 3d7 4s2
Electrons per shell	2, 8, 15, 2
Physical properties
Phase at STP	solid
Melting point	1768 K (1495 °C, 2723 °F)
Boiling point	3200 K (2927 °C, 5301 °F)
Density (near r.t.)	8.90 g/cm3
when liquid (at m.p.)	8.86 g/cm3
Heat of fusion	16.06 kJ/mol
Heat of vaporization	377 kJ/mol
Molar heat capacity	24.81 J/(mol·K)
Atomic properties
Oxidation states	−3, −1, +1, +2, +3, +4, +5(an amphoteric oxide)
Electronegativity	Pauling scale: 1.88
Ionization energies	1st: 760.4 kJ/mol; 2nd: 1648 kJ/mol; 3rd: 3232 kJ/mol; (more);
Atomic radius	empirical: 125 pm
Covalent radius	Low spin: 126±3 pm; High spin: 150±7 pm
	Spectral lines
	Spectral lines
Miscellanea
Crystal structure	hexagonal close-packed (hcp)
Speed of sound thin rod	4720 m/s (at 20 °C)
Thermal expansion	13.0 µm/(m·K) (at 25 °C)
Thermal conductivity	100 W/(m·K)
Electrical resistivity	62.4 nΩ·m (at 20 °C)
Magnetic ordering	ferromagnetic
Young's modulus	209 GPa
Shear modulus	75 GPa
Bulk modulus	180 GPa
Poisson ratio	0.31
Mohs hardness	5.0
Vickers hardness	1043 MPa
Brinell hardness	470–3000 MPa
CAS Number	7440-48-4
History
Discovery and first isolation	Georg Brandt (1735)
Main isotopes of cobalt
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Cobalt is a chemical element with symbol Co and atomic number 27. Like nickel, cobalt is found in the Earth's crust 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.

Cobalt-based blue pigments (cobalt blue) have been used since ancient times for jewelry and paints, and to impart a distinctive blue tint to glass, but the color was later thought by alchemists to be due to the known metal bismuth. Miners had long used the name kobold ore (German for goblin ore) for some of the blue-pigment producing minerals; they were so named because they were poor in known metals, and gave poisonous arsenic-containing fumes when smelted. In 1735, such ores were found to be reducible to a new metal (the first discovered since ancient times), and this was ultimately named for the kobold.

Today, some types of cobalt are produced specifically from one of a number of metallic-lustered ores, such as for example cobaltite (CoAs S). The element is however more usually produced as a by-product of copper and nickel mining. The copper belt in the Democratic Republic of the Congo (DRC), Central African Republic and Zambia yields most of the global cobalt production. The DRC alone accounted for more than 50% of world production in 2016 (123,000 tonnes), according to Natural Resources Canada.

Cobalt is primarily used in the manufacture of magnetic, wear-resistant and high-strength alloys. The compounds cobalt silicate and cobalt(II) aluminate (CoAl₂O₄, cobalt blue) give a distinctive deep blue color to glass, ceramics, inks, paints and varnishes. Cobalt occurs naturally as only one stable isotope, cobalt-59. Cobalt-60 is a commercially important radioisotope, used as a radioactive tracer and for the production of high energy gamma rays.

Cobalt is the active center of a type of coenzymes called cobalamins. vitamin B₁₂, the best-known example of the type, is an essential trace mineral for all animals. Cobalt in inorganic form is also a micronutrient for bacteria, algae, and fungi.