Question

The first electron affinity of C, N and O will be of the order:
A. $C < N < O$
B. $N < C < O$
C. $C < O < N$
D. $O < N < C$

Answer 1

Hint: We know the modern periodic table is based on the properties of an element that are functions of their atomic number. The properties are based on the electronic configuration of the elements. Periodic properties are the trend in properties across a period from left to right to down the group. Some of the important periodic properties are metallic character, non-metallic character, atomic size, electron affinity, ionization potential and electronegativity.

Complete step by step answer:
We can define electron affinity as the energy change of a neutral atom in the vapour phase when an electron is added to the atom to give a negative ion.
Electron affinity of the periodic table decreases down a group because each atom is larger than the above atom. The electron affinity increases across a period as the electrons move closer to the nucleus because of their smaller size and strong force of attraction.
In electron affinity, the atom gains electrons.
Oxygen belongs to group-16.
Nitrogen belongs to group-15.
Carbon belongs to group-14.
Now let us check for oxygen, nitrogen and carbon.
We know that electron affinity will increase from left to right in the periodic table due to the increase in nuclear charge.
In the given group of elements, carbon will be having the least electron affinity as lies as the first element to the left in the given group (carbon is seen before nitrogen and oxygen in period 2).
Oxygen will have the highest electron affinity among nitrogen and carbon.
Therefore, the order of electron affinity will be $O > N > C$.
But electron affinity of nitrogen is less due to its half-filled p orbital. Therefore, the order of electron affinity will be $N < C < O$.

So, the correct answer is Option B.

Note:
The trends of electron affinity are,
${\text{Halogens > Oxygen}}\,{\text{family > Carbon}}\,{\text{family > Nitrogen}}\,{\text{family > Metals}}\,{\text{groups}}\,{\text{1}}\,{\text{and}}\,{\text{13 > Metals}}\,{\text{group}}\,{\text{2}}$
Electron affinities of nonmetals are greater than metals.
The factors that affect electron affinity are atomic size and nuclear charge.
We can define first electron affinity as the energy given out by the first electron when it is added to an atom and it results in the formation of monovalent anion.
Example: The electron affinity of selenium is $ - 195\,kJ/mol$
The electron affinity of germanium is $ - 119\,kJ/mol$
The higher negative electron affinity value, the greater will be the atom’s affinity for electrons. Therefore, selenium has greater electron affinity than germanium.