Why are the group-2 metals harder and have higher melting and boiling points than group-I metals?

Explanation

Magnitude of the cohesive energy determines the hard- ness as well as melting and boiling points of the metals and it depends on the number of electrons involved in metallic bonding. In case of group 1 metals, one electron per atom (valence electron, ns1 ) is involved in metallic bonding while in group 2 metals, two electrons per atom ( valence electrons, `ns^2`) are involved in metallic bonding. Moreover, atoms of group 2 metals are smaller in size than that of group 1 metals. Consequently, stronger metallic bonding exists in group 2 metals which results in higher cohesive energy and close packing of the atoms. This accounts for the greater hardness and higher melting and boiling points of group 2 metals as compared to group 1 metals.