How do those electrons arrange themselves?
6. Elements are arranged in columns on the periodic table depending on how the electrons are filling the available orbitals. For instance (and in simple terms), those in column 1 have only 1 electron in the highest energy level set of orbitals. Those in column 2 have only 2 electrons. Those in column 17 are missing only 1. Those in column 18 have no missing electrons.