Term Types
| Number of "Outer" Electrons | Examples | Possible S values | Possible (2S + 1) values | Term Types |
| 0 (inert gases) | He, Ne, Ar, Kr, Xe, Rn | 0 | 1 | Singlets |
| 1 (alkali metals) | Li, Be II, Na, Mg II, K, Ca II | 1/2 | 2 | Doublets |
| 2 | Be, Mg, Ca, Sr, Ba | 0, 1 | 1, 3 | Singlets, Triplets |
| 3 | N, P, | 1/2, 3/2 | 2, 4 | Doublets, Quartets |
| 4 | O, S | 0, 1, 2 | 1, 3, 5 | Singlets, Triplets, Quintets |