**Spectroscopic notation**

To make life even more complicated, the * l*
quantum number values are often referred to using an old-fashioned

1s^{2},2s^{2},2p^{6},3s^{2},3p^{6},3p^{8}

Note that the last level could hold 10 electrons although only 8 were needed to reach 26.

Spectroscopic notation is convenient because chemical properties of atoms are primarily determined by either the number of electrons it takes to fill the last shell or the number of excess electrons beyond the last filled shell.