Ionisation Potential values depends on (a) atomic size (b) nuclear pull. Explain.

(a) The greater the atomic size the lesser the force of attraction. Since the electrons of the outermost shell lie further away from the nucleus, it makes their removal easier. Thus, Ionisation Potential decreases with increase in atomic size.

(b) The greater the nuclear charge, greater is the attraction for the electrons of the outermost shell. Therefore, the electrons in the outermost shell are more firmly held because of which greater energy is required to remove the electron(s). Thus, Ionisation Potential increases with increase in nuclear pull.