27
Co
Cobalt
58.933
Cobalt (Co)
Transition MetalGroup 9Period 4d-block-block
Cobalt is a chemical element with symbol Co and atomic number 27. Like nickel, cobalt in the Earth's crust is found 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.
Latin name: Cobaltum
Atomic Number
27
Atomic Mass
58.933 g/mol
Phase (STP)
Solid
Electron Config.
[Ar] 3d⁷ 4s²
General
SymbolCo
Atomic Number27
Atomic Mass58.933 g/mol
CategoryTransition Metal
Group9
Period4
Blockd-block
Electron Configuration[Ar] 3d⁷ 4s²
Valence Electrons9
Colourgreyish-metallic
Appearancehard lustrous gray metal
CAS NumberCAS7440-48-4
Physical Properties
Phase (STP)Solid
Density8.9 g/cm³
Melting Point1494.85°C · 2722.73°F · 1768.00 K
Boiling Point2926.85°C · 5300.33°F · 3200.00 K
Atomic Properties
Atomic Radius152 pm
Electronegativity1.88 Pauling
Ionization Energy760 kJ/mol
Oxidation States+2, +3
Ion ChargeCo2+/Co3+
Thermodynamic
Molar Heat24.81 J/(mol·K)
Crystal Structure
Crystal Structurehexagonal close-packed
Mechanical Properties
Mohs Hardness5
Abundance
In Earth's Crust0.0110%
Discovery & History
Discovery Year1735
Discovered ByGeorg Brandt
Country of DiscoverySweden
Isotopes of Cobalt
| Isotope | Abundance | Half-life | Decay |
|---|---|---|---|
| Co-57 | — | 271.74 days | EC |
| Co-58 | — | 70.86 days | β⁺, EC |
| Co-59 | 100% | Stable | — |
| Co-60 | — | 5.2713 years | β⁻ |