Question

Elements of Group $16$ generally show lower value of first ionization enthalpy compared to the corresponding periods of group $15$. Why?

Answer 1

Ionization enthalpy
Minimum energy required to remove most loosely bonded outer most shell $e^{-}$ in ground state from an isolated gaseous atom is known as ionization energy.

(Isolated → Without any bonding with other atom)

Ionization enthalpy of group $15$ and $16$ elements

Electronic configuration of group $15$ elements: $n{s}^{2}n{p}^3$

Electronic configuration of group $16$ elements: $n{s}^{2}n{p}^4$

Due to extra stable half-filled $p$ orbitals electronic configurations of group $15$ elements, the tendency of electron gains and loose is very less. Hence, if we want to remove electron from $n{p}^3$, larger amount of energy is required.