According to what my chemistry teacher said, the energy of a subshell is given by the sum of its principal quantum number (n) and its second quantum number (l).
- 1s = n+l = 1+0 = 1
- 2s = n+l = 2+0 = 2
- 2p = n+l = 2+1 = 3
- 3s = n+l = 3+0 = 3
However, when it comes to make a graphical representation of an electron configuration (which follows an order of increasing energy), she doesn't put the subshells having the same energy in the same level, like in the following picture:
Shouldn't the subshells 2p and 3s (which both have an energy equals to 3), as well as 4p and 3d, be put in the same level, since they have the same energy?