What is Hund's Rule?

sometimes refered to as the"empty bus seat rule" because when people get on a bus, they always sit by themselves unless all of the seats already have one person in all of them....then they are forced to pair up. Same with electrons. They inhabit empty orbitals, for example, there are 3 different p orbitals, px, py and pz (each in a different orientation). Electrons will fill them one at a time until each p has one electron in it (never pairing), and now the electrons are forced to pair up.

An example ##N##: