Cobalt
Atomic Number: 27
Symbol: Co
Atomic Weight: 58.9332
Discovery: George Brandt, circa 1735, maybe 1739 (Sweden)
Electron Configuration: [Ar] 4s2 3d7
Word Origin: German Kobald: evil spirit or goblin; Greek cobalos: mine
Isotopes: Twenty-six isotopes of cobalt have been identified. Cobalt-59 occurs naturally and is stable. Cobalt-48, cobalt-49, and cobalt-51 are not radioactive; the other sythesized isotopes are.
Properties: Cobalt has a melting point of 1495°C, boiling point of 2870°C, specific gravity of 8.9 (20°C), with a valence of 2 or 3. Cobalt is a hard, brittle metal. It is similar in appearance to iron and nickel. Cobalt has a magnetic permeability around 2/3 that of iron. Cobalt is found as a mixture of two allotropes over a wide temperature range. The b-form is dominant at temperatures under 400°C, while the a-form predominates at higher temperatures.
Uses: Cobalt forms many useful alloys. It is alloyed with iron, nickel, and other metals to form Alnico, an alloy with exceptional magnetic strength. Cobalt, chromium, and tungsten may be alloyed to form Stellite, which is used for high-temperature, high-speed cutting tools and dies. Cobalt is used in magnet steels and stainless steels. It is used in electroplating because of its hardness and resistance to oxidation. Cobalt salts are used to impart permanent brilliant blue colors to glass, pottery, enamels, tiles, and porcelain. Cobalt is used to make Sevre's and Thenard's blue. A cobalt chloride solution is used to make a sympathetic ink. Cobalt is essential for nutrition in many animals. Cobalt-60 is an important gamma source, tracer, and radiotherapeutic agent.
Sources: Cobalt is found in the minerals cobaltite, erythrite, and smaltite. It is commonly associated with ores of iron, nickel, silver, lead, and copper. Cobalt is also found in meteorites.
Element Classification: Transition Metal
Density (g/cc): 8.9
Melting Point (K): 1768
Boiling Point (K): 3143
Appearance: Hard, ductile, lustrous bluish-gray metal
Atomic Radius (pm): 125
Atomic Volume (cc/mol): 6.7
Covalent Radius (pm): 116
Ionic Radius: 63 (+3e) 72 (+2e)
Specific Heat (@20°C J/g mol): 0.456
Fusion Heat (kJ/mol): 15.48
Evaporation Heat (kJ/mol): 389.1
Debye Temperature (K): 385.00
Pauling Negativity Number: 1.88
First Ionizing Energy (kJ/mol): 758.1
Oxidation States: 3, 2, 0, -1
Lattice Structure: Hexagonal
Lattice Constant (Å): 2.510
References: Los Alamos National Laboratory (2001), Crescent Chemical Company (2001), Lange's Handbook of Chemistry (1952), CRC Handbook of Chemistry & Physics (18th Ed.)
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