... there is a drop from neon, which has a full outer shell to sodium which has one electron in its outer shell. The only reason for this drop would be that the effect nuclear charge has dropped. The ENC has dropped, although the nuclear charge has increased, because the new electron must have joined a new shell, and is thus further away from the nucleus as well as experiencing more shielding. This is why less energy is required to make a gaseous atom of sodium into an ion, as the electron in its outer shells is easier to remove, due to less attraction between it and the nucleus. As we move on, the next element up, magnesium, we can see that more energy is required to remove the extra electron added to the shell. This is because the nucleus has a higher effective nuclear charge and therefore, a greater force of ...

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