Cobalt (Co)
[Ar] 3d⁷ 4s². 3 unpaired electrons, period 4, group 9, d block.
Element or ion
Type a symbol, a name or an atomic number, add a charge such as Fe3+ or Cl-, or tap an element in the table. Orbitals fill from m = −l up, spin +½ first.
CoCobalt, Z = 27, 58.933 u
[Ar] 3d7 4s2
In full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁷ 4s²
- Blockd block
- Period4
- Group9
- Valence9
- Unpaired3
- MagneticPara
Last electron 3d
- n3shell
- l2d subshell
- m−1orbital
- s−½spin down
Step by step
- Cobalt has 27 electrons.
- Fill in (n + l) order: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁷.
- Write the subshells in order of n: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁷ 4s².
- Replace the argon core with [Ar]: [Ar] 3d⁷ 4s².
Cobalt (Co): the numbers
| Atomic number | 27 |
|---|---|
| Atomic mass | 58.933 u |
| Period | 4 |
| Group | 9 |
| Block | d block |
| Valence electrons | 9 |
| Unpaired electrons | 3 |
| Magnetic | paramagnetic |
| Last electron | 3d: n = 3, l = 2, m = −1, s = −1/2 |
Cobalt (Co): quick answers
What is the electronic configuration of cobalt?
Cobalt has 27 electrons: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁷ 4s², or [Ar] 3d⁷ 4s² in short.
How many unpaired electrons does cobalt have?
Cobalt has 3 unpaired electrons, so it is paramagnetic. Put one electron in each box of a subshell before pairing (Hund’s rule) to see them.
What are the quantum numbers of the last electron of cobalt?
The last electron goes into 3d: n = 3, l = 2, m = −1, s = −1/2. Orbitals fill from m = −l up, spin +½ first.