Question

How does Hund's rule of maximum multiplicity suggest what one can predict for a stable configuration?

Answer 1

Hund's rule basically asks you to maximize the number of parallel electron spins to get the most stable electronic configuration.

So two examples of `2p^3` configurations that are not as stable as they could be:

`ul(darr color(white)(darr))" "ul(uarr color(white)(darr))" "ul(uarr color(white)(darr))`

`ul(darr uarr)" "ul(uarr color(white)(darr))" "ul(color(white)(uarr darr))`

The ground state configuration, i.e. most stable, would be:

`ul(uarr color(white)(darr))" "ul(uarr color(white)(darr))" "ul(uarr color(white)(darr))`

The first example does not have all parallel spins. Electrons are indistinguishable, so quantum mechanics states that they could have exchanged if they were the same spin. If they can't, the configuration is less stable.

The second has electrons pairing up before filling up all the orbitals first, which adds electron repulsion and destabilizes the system.