Cobalt (Co): Electron Configuration, Properties and Uses
Cobalt (Co): Electron Configuration, Properties and Uses
Electron configuration [Ar] 4s2 3d7 · group 9 · period 4 · Ar 58.933
Cobalt data
- Atomic number
- 27
- Relative atomic mass
- 58.933
- Group
- 9
- Period
- 4
- Block
- d
- Category
- Transition metal
- Electron configuration
- [Ar] 4s2 3d7
- Full configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d7
- Electrons per shell
- 2, 8, 15, 2 (K L M N)
- Valence electrons
- 9
- Electronegativity (Pauling)
- 1.88
- First ionisation energy
- 7.881 eV
- Atomic radius (van der Waals)
- 192 pm
- State at room temperature
- Solid
- Melting point
- 1495 °C
- Boiling point
- 2927 °C
- Density
- 8.86 g/cm³
- Common oxidation states
- +3, +2
- Discovered
- 1735
Source: PubChem (NIH, accessed 13 Nov 2026); atomic mass: IUPAC standard atomic weight.
Electron shell diagram
K 2 · L 8 · M 15 · N 2
Orbital diagram (outer electrons)
About cobalt
Cobalt is a chemical element with the symbol Co and atomic number 27. It is a transition metal in group 9, period 4, d-block. The element was discovered in 1735. Cobalt is a solid at room temperature, melting at 1495 °C and boiling at 2927 °C.
Cobalt electron configuration
The electron configuration of cobalt is 1s2 2s2 2p6 3s2 3p6 4s2 3d7, or in short [Ar] 4s2 3d7. Its electrons occupy 4 shells: K = 2, L = 8, M = 15, N = 2. For transition metals, valence electrons are counted from the 4s and 3d subshells: 2 + 7 = 9, matching group 9. When it forms cations, electrons leave the outermost subshell first: Co2+ = [Ar] 3d7; Co3+ = [Ar] 3d6.
Filling order: 1s2(2) → 2s2(4) → 2p6(10) → 3s2(12) → 3p6(18) → 4s2(20) → 3d7(27)
Uses of cobalt
The main uses of cobalt include lithium battery cathodes (LCO and NMC), turbine superalloys, cobalt blue pigment and vitamin B12. For research and analysis you can browse cobalt compounds in the AMI Scientific catalogue.
Safety
Cobalt compounds can cause skin and respiratory sensitisation, and some are suspected carcinogens. Always read the safety data sheet (SDS) before working with a chemical.
Other elements in group 9
Frequently asked questions
What is the electron configuration of cobalt?
The electron configuration of cobalt (Co, atomic number 27) is 1s2 2s2 2p6 3s2 3p6 4s2 3d7, or [Ar] 4s2 3d7 in short. By shell: 2, 8, 15, 2.
How many valence electrons does cobalt have?
Cobalt has 9 valence electrons.
Which group and period is cobalt in?
Cobalt is in group 9, period 4, d-block.
What is the atomic mass of cobalt?
The relative atomic mass of cobalt is 58.933. Use it to calculate molar mass with the molar mass calculator.
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