Cobalt

Cobalt,  ₂₇Co

General properties
Name, symbol	Cobalt, Co
Appearance	Lustrous gray metal
Cobalt in the periodic table
- ↑ Co ↓ Rh Iron ← Cobalt → Nickel
Atomic number	27
Standard atomic weight (Ar)	58.933194(4)
Group, block	9; d-block
Period	period 4
Electron configuration	[Ar] 3d7 4s2
per shell	2, 8, 15, 2
Physical properties
Silvery-gray
Phase	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	8.86 g/cm3
Heat of fusion	16.06 kJ/mol
Heat of	377 kJ/mol
Molar heat capacity	24.81 J/(mol·K)
pressure
Atomic properties
Oxidation states	−3, −1, +1, +2, +3, +4, +5 ​(an amphoteric oxide)
Electronegativity	Pauling scale: 1.88
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
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 Ω·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
CAS Registry Number	7440-48-4
History
Discovery	Georg Brandt (1732)

Cobalt is a chemical element with symbol Co and atomic number 27.

Properties

Chemical

Cobalt is a weakly reducing metal, resistant to oxidation, by forming a passivating oxide film. At room temperature, cobalt reacts slowly with mineral acids, and very slowly with moist, but not with dry, air. Hot cobalt reacts with oxygen to give cobalt(II,III) oxide, which converts to cobalt monoxide CoO at 900 °C. Cobalt reacts with many nonmetals, such as molten sulfur, boron, phosphorus, arsenic, carbon. It also reacts with halogens, giving cobalt(III) halides. Cobalt however does not react with hydrogen gas or nitrogen gas even at high temperatures. As such, annealed cobalt alloys are sometimes used to store hydrogen.

Physical

Cobalt is a hard, lustrous, silver-gray metal. Like iron, nickel and gadolinium (under 20 °C), cobalt is ferromagnetic

Availability

Cobalt is sold by various chemical suppliers.

Old Alnico magnets contain cobalt, which can be extracted through various methods.

In European Union, most cobalt compounds are classified as "Substance of very high concern" in the EU and their sale is regulated.

Isolation

Cobalt metal can be made by reducing cobalt oxides with carbon, hydrogen or aluminium. Very pure cobalt can also be obtained electrolytically.

Projects

• Make cobalt blue
• Make various colorful cobalt coordination complexes
• Make lithium cobalt oxide battery

Handling

Safety

Cobalt and its compounds display toxicity. It is an essential trace element only in minute quantities. The LD₅₀ value for soluble cobalt salts has been estimated to be between 150 and 500 mg/kg. Cobalt is known to cause contact dermatitis.

Cobalt is the active center of coenzymes called cobalamins, the most common example of which is vitamin B12. As such it is an essential trace dietary mineral for all animals.

Storage

Cobalt should be stored in closed containers away from corrosive vapors.

Cobalt powder should be kept in sealed containers or bottles, preferably in an oxygen free environment, to prevent oxidation.

Disposal

Cobalt should be taken to disposal centers.

References

Relevant Sciencemadness threads

• Cobalt acquisition?
• thf and cobalt