Cobalt, Co, has 27 electrons. Write out the entire electron configuration for cobalt using spdf notation.

Co = 1s2 2s2 2p6 3s2 3p6 4s2 3d7

Explanation:

Number of electrons = 27

The closest noble gas before cobalt is Argon and argon has 18 electrons.

Co = [Ar]  ; Remains 27 - 18 = 9  more electrons to fill.

The next orbital in order of increasing energy is the 4s orbital. However it can only hold a maximum of 2 electrons.

We have;

Co = [Ar] 4s2; Remains 27 - 20 = 7 more electrons to fill.

The next orbital in order of increasing energy is the 3d orbital. It can have a maximum of 10 electrons.

So we have;

Co = [Ar] 4s2 3d7

The electronic configuration of Ar = 1s2 2s2 2p6 3s2 3p6

This means the entire configuration of cobalt is;

Co = 1s2 2s2 2p6 3s2 3p6 4s2 3d7