Cobalt Facts and Physical Properties

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 ranging from Co-50 to Co-75. Co-59 is the only stable isotope.

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

Cobalt Physical Data

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

CAS Registry Number: 7440-48-4

Cobalt Trivia

• Cobalt derived its name from German miners. They named cobalt ore after mischievous spirits called kobalds. Cobalt ores commonly contain the useful metals copper and nickel. The problem with cobalt ore is it usually contains arsenic as well. Attempts to smelt the copper and nickel typically failed and would often produce arsenic oxide gases.
• The brilliant blue color cobalt gives to glass was originally attributed to bismuth. Bismuth is often found with cobalt. Cobalt was isolated by Swedish chemist, Georg Brandt who proved the coloring was due to cobalt.
• The isotope Co-60 is a strong gamma radiation source.
• Cobalt is a central atom in vitamin B-12.
• Cobalt is ferromagnetic. Cobalt magnets stay magnetic to the highest temperature of any other magnetic element.
• Cobalt has six oxidation states: 0, +1, +2, +3, +4, and +5. The most common oxidation states are +2 and +3.
• The oldest cobalt colored glass was found in Egypt dated between 1550-1292 B.C.
• Cobalt has an abundance of 25 mg/kg (or parts per million) in the Earth's crust.
• Cobalt has an abundance of 2 x 10^-5 mg/L in sea water.
• Cobalt is used in alloys to increase temperature stability and decrease corrosion.

References: Los Alamos National Laboratory (2001), Crescent Chemical Company (2001), Lange's Handbook of Chemistry (1952), CRC Handbook of Chemistry & Physics (18th Ed.) International Atomic Energy Agency ENSDF database (Oct 2010)

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