027Transition metal · Group 9 · Period 4
Cobalt
Cobalt (Co) is element 27, a transition metal in the d-block — group 9, period 4. It is a solid at room temperature with 4 electron shells (2, 8, 15, 2) and an atomic mass of 58.9331944 u.
- Atomic mass
- 58.93 u
- Phase · STP
- solid
- Melting
- 1768 K · 1495 °C
- Boiling
- 3200 K · 2927 °C
- Electronegativity
- 1.88
- Density
- 8.9 g/cm³
Photograph — Hi-Res Images ofChemical Elements, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons, source: https://images-of-elements.com/cobalt.php
Identity
- Atomic number
- 27
- Standard atomic weight
- 58.93 u
- Category
- Transition metal
- Group
- 9
- Period
- 4
- Block
- d-block
- Oxidation states
- +3, +2
Physical properties
- Melting point
- 1768 K · 1495 °C
- Boiling point
- 3200 K · 2927 °C
- Density
- 8.9 g/cm³
- Molar heat capacity
- 24.81 J/(mol·K)
- Atomic radius
- 192 pm
- Electron affinity
- 63.898 kJ/mol
Atomic structure
27protons
32neutrons
27electrons
2valence e⁻
- Noble-gas notation
- [Ar] 3d7 4s2
- Full configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d7
- Electrons per shell
- 2, 8, 15, 2
Periodic trends
Where Cobalt ranks across all 118 elements.
Ionization energies
Energy to remove each successive electron (kJ/mol).
760.41
1.6k2
3.2k3
5.0k4
7.7k5
9.8k6
12.4k7
15.2k8
18.0k9
26.6k10
Successive ionization energies (kJ/mol, log scale).
Discovery
- Discovered
- 1735
- Discovered by
- Georg Brandt
- Named by
- —
- Appearance
- hard lustrous gray metal