Electronic configuration of cobalt

Electrons in each shell

Cobalt has 27 electrons arranged as 2, 8, 15, 2 across 4 shells, which is why it sits in period 4.

How to write it

Electrons fill orbitals in order of increasing energy: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p… Each s orbital holds 2 electrons, p holds 6 and d holds 10. Placing Cobalt's 27 electrons in that order gives 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁷.

Cobalt at a glance

Other elements in group 9