PAULI PRINCIPLE (EXCLUSION PRINCIPLE; PAULI EXCLUSION; PAULI EXCLUSION PRINCIPLE)

No two electrons in an atom can have the same set of 4 quantum numbers. Because the n, , and m quantum numbers address a particular orbital, and because the ms quantum number has only two possible values, the Pauli principle says that a maximum of two electrons can occupy an atomic orbital- and these electrons must have opposite spins.