In the series Sc (Z = 21) to Zn (Z = 30), the enthalpy of atomization of zinc is the lowest, i.e., 126 kJ mol–1. Why?
The enthalpy of atomization depends on the strength of the metallic bonding. Stronger the metallic bonding, greater is the enthalpy of atomization. The metallic bonding is strong when there are more unpaired electrons in the atom. All transition metals (except Zn, electronic configuration: [Kr] 3d10 4s2), have at least one unpaired electron that is responsible for their stronger metallic bonding. Since the Zn atom does not have an unpaired electron, the metallic bonding is weak and hence the enthalpy of atomization is low.