Question

The increasing order of electron affinity of the electronic configurations of element is:
A. $1{{\text{s}}^2}2{{\text{s}}^2}2{{\text{p}}^6}3{{\text{s}}^2}3{{\text{p}}^5}$
B. $1{{\text{s}}^2}2{{\text{s}}^2}2{{\text{p}}^3}$
C. $1{{\text{s}}^2}2{{\text{s}}^2}2{{\text{p}}^5}$
D. $1{{\text{s}}^2}2{{\text{s}}^2}2{{\text{p}}^6}3{{\text{s}}^1}$
(1) A>D>C>B
(2) B>D>C>A
(3) C>D>B>A
(4) D>A>C>B

Answer 1

Hint: The given options show the electronic configurations of different elements. A, B, C, D represents the elements. The periodic trends of electron affinity is related to the number of shells and electrons.

Complete step by step solution:
The energy change occurred when $1{\text{mol}}$ of electrons are added to $1{\text{mol}}$ of gaseous ions atoms. Atoms are added with electrons to form ions. Thus energy is released because of the force of attraction of electrons to the positive charge in the nucleus.
i.e. ${\text{A}} + {{\text{e}}^ - } \to {{\text{A}}^ - }$
Electron affinity is expressed in ${\text{kJ}}.{\text{mo}}{{\text{l}}^{ - 1}}$ or ${\text{eV}}$ per atom.
On moving down the group in periodic table, new shells are added to the atom. Thus the force of attraction is decreased. So the electron affinity is decreased.
While moving from left to right in the periodic table, the number of electrons are added. So the nuclear charge of atoms is increased. It is attracted to the incoming electrons. So the electron affinity is also increased.
The element A has three shells having electrons as $2,8,7$. B has two shells having electrons as $2,5$. C has two shells with electrons $2,7$ and D has three shells with electrons $2,8,1$.
Among these elements, C has the highest electron affinity because it has more nuclear charge, thus more energy is required. ${\text{2p}}$ is more close to the nucleus. In element D, ${\text{3s}}$ orbital needs one more electron. In element A, the ${\text{3p}}$ electrons are very far from the nucleus. So the nuclear charge is less. So the electron affinity will be least when compared to other elements.
Thus the order is C>D>B>A

Hence, the correct option is (3).

Note: First electron affinity is negative. But for further addition of electrons, electron affinity value is positive. This is because when the electrons are added, there will be repulsion between electrons and nucleus. So more energy will be released to overcome this repulsion.