Explain how successive ionization energies account for the existence of three main energy levels in the sodium atom.

Make the student observe and analyse the electronic configuration of sodium and the trends in ionization energies for this element. We note a large increase in ionization energy between the 1st and 2nd electrons and between the 9th and 10th electrons. The large increase in ionization energy means that there is a much greater nuclear charge on the successive electrons as we get closer to the nucleus. The extent of this difference for those specific electrons shows that the the second electron is much closer to the nucleus that the first one, meaning that we have changed energy level. The same thing applies for the 9th and 10th electrons. Given that we noted 2 significant increases in energy levels, this shows that there are 3 main energy levels.(Support this with a diagram for better understanding).