Question

The correct order of electron affinity of ${\text{B,}}\,{\text{C,}}\,{\text{N,}}\,{\text{O}}$ is:
A. ${\text{O > }}\,{\text{C}}\,{\text{ > }}\,{\text{N}}\,{\text{ > }}\,{\text{B}}\,$
B. $\,\,{\text{B}}\,{\text{ > }}\,{\text{N}}\,{\text{ > }}\,{\text{C}}\,{\text{ > }}\,{\text{O}}\,$
C. ${\text{O > }}\,{\text{C}}\,{\text{ > }}\,{\text{B}}\,{\text{ > }}\,{\text{N}}$
D. ${\text{O}}\,{\text{ > }}\,{\text{B}}\,{\text{ > }}\,{\text{C}}\,{\text{ > }}\,{\text{N}}$

Answer 1

Hint: The electron affinity is the power of a neutral atom to accept an electron. Electron affinity increases left to right and decreases, down in a group. It depends on the effective nuclear charge that an atom in the periodic table consists of.

Complete Step by step answer: The electron affinity is defined as the energy change on the addition of an electron to a neutral atom.
On going left to right in the periodic table, the electron affinity increases because the distance between the nucleus and outermost shell decreases, so the attraction of the nucleus and electrons of the outermost shell increases hence the added electron gets stabilization.
On going down in a group in the periodic table, electron affinity decreases because the principal quantum number of the outermost shell increases hence the distance between outermost shell electrons and the nucleus increases, so the added electron does not get stabilized by the nucleus.
The atoms having half-filled or fully-filled electronic configuration are the exceptions of the general trend. Due to the high stability of half-filled or fully-filled electronic configuration, the atoms have very low electron affinity.
So, according to the general trend, the electron affinity order will be,
${\text{O > }}\,{\text{N}}\,{\text{ > }}\,{\text{C}}\,{\text{ > }}\,{\text{B}}$
The nitrogen has a half-filled electronic configuration, so its tendency to accept electrons is very-very less than carbon and boron. So, the electron affinity order is as follows:
${\text{O > }}\,{\text{C}}\,{\text{ > }}\,{\text{B}}\,{\text{ > }}\,{\text{N}}$

Therefore, option (C) ${\text{O > }}\,{\text{C}}\,{\text{ > }}\,{\text{B}}\,{\text{ > }}\,{\text{N}}$ is correct.

Note: Any factor which disfavour the addition of the electron will decrease the electron affinity. On the addition of an electron, the energy releases so, the electronegative affinity is negative. The negative sign shows the release of energy. However, only first electron affinity has a negative sign. Second and other electron affinities have a positive sign.