How does the first ionization enthalpy change down group 2?

First ionization enthalpy is the energy required to remove one electron from each atom in one mole of gaseous atoms, forming one mole of gaseous 1+ ions. The first ionization enthalpy is largely dependent on the electrostatic attraction between the nucleus and the outer shell electrons (OSE).This force is affected by 3 factors:1.      Atomic radii (size of atom)2.      Nuclear charge3.      ShieldingAs we are in the same group we can ignore the effect of nuclear charge – this does not change.Down the group atomic radii increases as the atoms gain more electron shells.Shielding – this is an effect where the shells of electrons between the nucleus and the OSE effectively cancel out some of the charge from the nucleus. As the number of electron shells between the nucleus and the OSE increases, the effect of shielding increases.As a result of increased shielding and greater atomic radii, the first ionization enthalpy decreases down the group – i.e. it requires less energy to remove the electron