The two spin orientations are designated and .
Whenever two electrons are in the same orbital, they must have opposite spins. This is a
consequence of the Pauli exclusion principle; if that were not the case, they would have the identical
four quantum numbers. Electrons in different orbitals with the same ms values are said to have
parallel spins. Electrons with opposite spins in the same orbital are often referred to as paired.
For the shell corresponding to n = 3, a complete enumeration of the possible sets of quantum
numbers follows. Note that the total number of electrons in this shell is 18 = 2 (3)^2.
QUICK QUIZ
In what order are subshells filled?Answer = (A)(A) lowest to highest energy
(B) highest to lowest energy
(C) randomly