In general, greater the number of unpaired electrons, greater is the number of bond and therefore, greater is the strength of these bonds, thus higher will be enthalpy of atomization.
Enthalpy of atomization first increases in a series (as unpaired electrons increases from 1 to 6 ), reaches to maxima and then decreases, and it is lowest for Zn,Cd,Hg (due to 0 unpaired electrons).