Ionisation Enthalpy

Ionisation enthalpy falls steadily on moving down Group 15, a direct consequence of the gradual increase in atomic size, which pulls the outermost electron further from the nucleus and makes it easier to remove. Even so, at any given period the Group 15 elements have distinctly higher ionisation enthalpies than their Group 14 neighbours — the half-filled $p^3$ configuration together with a comparatively small atomic size combine to hold onto electrons more tightly. As with any element, the successive ionisation enthalpies rise sharply in the order $\Delta_iH_1 < \Delta_iH_2 < \Delta_iH_3$ ( …