[SOLVED] What forces the 3rd electron to form a 2s state? Helium can handle two electrons as long as the spin of one is opposite to the other. Lithium has 3 electrons, 3 protons and 3 neutrons. If one electron is ionized producing a 1+ ion, and it is then exposed to a source of low energy electrons, why does Li (1+) add the "new" electron to a 2s state? What forces are at work?