Ionization energy is the amount of energy required to remove the outermost electron of a gaseous atom or ion.
Therefore, larger is the size of an atom more easily it will loose an electron as there will be weak force of attraction between the nucleus and outermost electrons.
Thus, there will be a change in ionization energy as the size of atom increases.
Hence, we can conclude that the attractive force on the valence electrons decreases as the atom gets larger.
