How many unpaired electrons are in a iron atom?

1 Answer
Feb 20, 2017

There are four unpaired electrons in the #3d# subshell of iron.


The ground state configuration of Fe is

#[Ar] 4s^2 3d^6#

The #4s# electrons are paired, and with six electrons in the #3d# subsell, Hund's rule tells us these will consist of one pair and four single, unpaired electrons.

(If you are not familiar with Hund's rule, it states that when electrons populate a set of orbitals having identical energy - such as the five #3d# orbitals - they do so by placing one electron in each orbital until all the orbitals are half-filled, then the electrons start to form pairs.)