ELECTRON CONFIGURATIONS
For n 1, the only value possible for both l and m is 0. Therefore, there is only a single state possible, the
one for n 1, l 0, and m 0. This state is denoted as the 1 s state. If n 2, it is possible for l to be 0 or
1. For the l 0 state, the n 2 and l 0 combination gives rise to the 2 s state. Again, m 0 is the only
possibility because of the restriction on the values of m being 0 up to l . Two electrons can be accom-
modated in the 2 s state, which is fi lled in the beryllium atom, so the electron confi guration is 1 s
2 2 s
2 .
For the quantum state for which n 2 and l 1, we fi nd that there are three values of m possible, 1,
0, and 1. Therefore, each value of m can be used with spin quantum numbers of 1/2 and 1/2