Ionisation of energy is the amount of energy needed to remove an electron from outer most shell of an atom. as the attraction between the nucleus and outer most electron increases the ionisation energy increases. Electronegativity is the relative measure of the force of attraction between an atom and the electron it is sharing in bond with other atom. electronegativity decreases as it goes down the group.
In conclusion:
As an atom gain an electron the atomic radius of the atom increase and the ionisation energy also increases but the electronegativity decrease as the atoms in outer most shell move further apart from the nucleus.