Hund's Rule [ENDORSED]

[Leslie Contreras 1D]

I keep re reading "due to electron repulsion electrons in the same subshell occupy different orbitals with parallel spins (lowest energy)"
But I do not entirely know what it means

[Luis Avalos 1D]

Hund's rule is just stating that electrons cannot have paired spins until the other orbitals are all filled first.

[Garrett Dahn 1I]

In practice, all this means is that when you are apportioning your electrons into their respective orbitals, you will not have paired spins (↑↓) until you've first filled all of the slots in the orbital once. The whole conceit behind this is that electrons are lazy and want to occupy the lowest energy level possible. So if you are an electron, you are looking for an "empty" orbital instead of an orbital with an electron already present. If there are no "empty" orbitals, the electron will cut its losses and pair (with reverse spins) with another electron.

For example, if you're creating an Aufbau diagram for Carbon, there is a lone pair of electrons in the valence shell because Hund's Rule asserts that electrons won't pair until they have to. Thus, the diagram looks like this:

2p (↑ ) (↑ ) ( )
2s (↑↓)
1s (↑↓)

Instead of this:

2p (↑↓) ( ) ( )
2s (↑↓)
1s (↑↓)

Hope this helps!

[Neha Divi 1K]

Another way to think of Hund's Rule is thinking about how people sit on a school bus. People are more likely to sit in a seat by themselves before sitting next to someone else. Electrons in orbitals act the same way. There will not be paired electrons until each one occupies one spot in an orbital.

[Cameron Smith 1I]

Why can hunds rule be broken in the excited state? What does the excited state imply?

[YeseniaGomez_1L]

I agree with everyone about but put easier The hund’s rule basically just says that electrons will enter the empty orbitals first, then start pairing when all are full.

[Sarai Ventura 1L]

Hund's rule is that every orbital in a subshell must be occupied with one electron before any one orbital is doubly occupied.