Electron sub shell

[205696437]

For each electron sub shell how can we tell if they're paired or parallel?

[Katie Shi 1F]

When electrons are filling up an outermost subshell they will prefer to stay parallel for as long as possible according to electron repulsion (Hund's Rule). Therefore, electrons will take up each orbital one by one until they are forced to pair with each other. Full subshells, ie any under the outermost subshell, will have all paired electrons.

[Emily Wan 1l]

According to the Pauli exclusion principle, two electrons filling an orbital will always be paired (run antiparallel and have opposite spin).