Since the first value that can be assigned to n is 1, electrons can occupy the first shell, leaving 8 electrons. The next value for n is 2. electrons may be assigned to the second shell, accounting for all electrons. The next step is to assign subshells. For n=1, l=0, which corresponds to the s subshell. For l=0, m=0, so there can be only one orbital within the s subshell. The two electrons assigned to the first shell must therefore both occupy the same subshell and orbital. By the Pauli exclusion principle, their spins must be opposite (one with up spin, the other with down spin). For the shell n=2, l=0 and 1. The electrons occupying the subshell corresponding to l=0 occupy the s subshell in the second shell. These electrons must therefore occupy the same orbital and have opposite spins. For l=1, m=-1, 0, and 1. The second subshell (p subshell) therefore has three orbitals. Each orbital can hold two electrons. Each pair of electrons has one electron with up spin and one with down spin. A total of six electrons may occupy the p subshell in the second shell, accounting for all of the electrons in the neon atom.
Electrons fill orbitals according to a specific order. They first fill the lowest energy levels and then fill higher energy levels. It requires more energy to orbit a nucleus that is far away than one that is close, so the lower shells fill first. Electron shells farther from the nucleus deviate slightly from this general guide. The
