CHM120H5 Lecture Notes - Lecture 8: Electron Configuration, Pauli Exclusion Principle, Atomic Number
Document Summary
Electrons will occupy a set of degenerate orbitals with parallel spin as far as possible. But other combinations are also possible, but they are of higher energy or excited states. An orbital can only hold two electrons and they must have opposite spin. Otherwise, the third or second electron would have the same 4 quantum numbers as an already existing electron in the atom. A half-filled shell has higher ionization energy than a fully-filled shell. Excess energy is needed to remove it because of increased attraction. If a shell is very stable, excess energy is needed to remove an electron. There is repulsion between the two electrons in an orbital together, so it"s easier to remove one. However, a fully filled configuration is more stable than a bunch of half-filled orbitals. Be has s2 completely filled and is stable. B has only one electron in 2p so it can be removed easily.
