Explain the trend in ionisation enthalpy with
reference to group 16.

Explanation

The ionisation enthalpy of group 16 elements has quite high
values.
(ii) Ionisation enthalpy decreases down the group from oxygen to
polonium. This is due to the increase in atomic volume down the group.
(iii) The first ionisation enthalpy of the lighter elements of group 16
(O, S, Se) have lower values than those of group 15 elements in the
corresponding periods. This is due to difference in their electronic
configurations.
Group 15 : (valence shell) `ns^(2)np_(x)^(1)np_(y)^(1)np_(z)^(1)`
Group 16 : (valence shell) `ns^(2)np_(x)^(2)np_(y)^(1)np_(z)^(1)`
Group 15 elements have extra stability of half filled and more
symmetrical orbitals, while group 16 elements acquire extra stability
by losing one of paired electrons from `np_(x)-`orbital forming half filled
p-orbitals.