Why do metals generally have lower ionization energies than non-metals? I mean, doesn't ionization energy depend on the atomic radius? And the atomic radius is in turn dependent on the shell and the protons. According to these factors, the atomic radius of Sodium should be smaller than lower period non-metals such as Bromine. Smaller atomic radius means that the proton can attract valence electrons much more strongly. Therefore, Sodium's IE must be higher than that of Bromine. But it's not the case. Why???