What are the various factors due to which the ionization enthalpy of the main group elements tends to decrease down a group?
On moving down the group, in main group elements the ionization energy regularly decreases due to the following factors.
(i) Atomic size: On moving down the group, as additional shells are added, the atomic size increases.
(ii) Shielding effect: As the number of inner electrons increases, the shielding effect on the outermost electrons increases.
(iii) Nuclear charge: On moving from top to down in a group, the nuclear charge increases. The effect of increase in the atomic size and the shielding effect is much more significant than the nuclear charge. The electron becomes less lightly held to the nucleus on moving down the group.
Due to this, the ionization enthalpies gradually decrease on moving down the group.