Now, if we look at the electron configuration for Bromine, which has 35 35 protons and 35 electrons, we see the following electron configuration. Now, this guy makes sense because one S comes before two S and two S comes before two P and two P comes before three S, and three S comes before three P. In other words, this goes from lowest energy level to highest energy level. And since we just said that four S is at a lower energy level than 3D, it would make sense to place the four S two before the this would be the correct election configuration if you're actually ordering from lowest energy level to highest energy level. But this doesn't have to be the case. In other words, if I flip these guys, that isn't wrong. That's allowed.