Electron configuration and the 2p orbital

When drawing orbital diagrams I know electrons are placed in the 2p boxes singly first then paired because of they have parallel rotations and the Pauli exclusion principle states that an orbital can only house 2 electrons and those electrons must be of opposite spin. My question is why do electrons behave this way in the 2p orbital but not the 1s or 2s? And why does the p subshell contain three 2p orbitals?

As far as electron configurations and orbital diagrams are concerned I've gotten to Ne and the 2p configuration confused me so I though I'd ask before moving on.

• they have parallel rotations . Electrons do not rotate. They are not little classical balls orbiting the nucleus. why do electrons behave this way in the 2p orbital but not the 1s or 2s. What do you mean by this? The Pauli exclusion principle applies for all electrons. – bon Nov 14 '15 at 20:08
• I mean why do the three 2p orbitals fill singly first then pair up instead one orbital filling up at a time. – Chinasa Nov 14 '15 at 20:25
• Because the 3 p-orbitals are degenerate but putting two electrons into the same orbital (with opposite spin of course) has an energy cost associated with the repulsion between the electrons. – bon Nov 14 '15 at 20:30
• Cross posted to Physics SE. Bad form... – Jon Custer Nov 14 '15 at 20:39
• Thats not allowed? What wrong with different answers from different people? – Chinasa Nov 14 '15 at 20:49