Ionization Enthalpy

The alkali metals have the lowest ionization enthalpies of any group, and these fall further on descending from Li to Cs. Two opposing effects act as atomic number increases: the growing nuclear charge, which would tend to hold the outer electron more tightly, and the growing atomic size together with greater shielding by inner shells, which loosens it. For this group, the size/shielding effect wins decisively over the rising nuclear charge, so the net outcome is that the lone v …