Question

The low electron affinity value of nitrogen is due to:
a.) small size
b.) high nuclear charge
c.) half-filled 2p subshell
d.) high metallic character

Answer 1

Electron Affinity is the energy associated with the addition of an electron to a gaseous atom. Hence, Electron affinity is defined as the change in energy (in kJ/mol) of a neutral atom (in the gaseous phase) when an electron is added to the atom to form a negative ion. As you move down a group on the periodic table, electron affinity decreases.

Complete step by step answer:
Atoms with a low electron affinity want to give up their valence electrons because they are far from the nucleus, as a result, they do not have a strong pull on the valence electrons

In the ground state, Stable half-filled configuration of Nitrogen atoms is $1{s^2}2{s^2}2{p^3}$. In this configuration the $2p$ subshell is half filled in the atom of the gaseous nitrogen. Hence this nitrogen atom will try to give up its valence electrons. Hence this is having low electron affinity due to the half-filled $2p$ subshell.
So, the correct answer is “Option C”.

Note: The electron affinity sometimes expressed as positive electron affinity and Negative electron affinity. Negative electron affinity refers to the attraction for an electron. (since an unbound electron has zero electron affinity), while the higher an atom's tendency to accept an electron, the more positive the electron affinity value will be.
There are some related exceptions too. In general, exceptions arise when new subshells are being filled/half-filled, or in cases where the atom is too small. In the first case, Be and Mg are interesting examples: they have a positive electron affinity (just like N, in fact) because of the energy difference between the s and p subshells.