Question

The correct order of electron affinity is?
(A) F > Cl > Br
(B) F > Cl < Br
(C) Cl > F > Br
(D) F < Cl > Br

Answer 1

Hint: You should know that the electron affinity is defined as the change in energy of a neutral atom when an electron is added to the atom to form a negative ion. Now, using this concept try to give the correct order of the electron affinity.

Complete step by step answer:
Remember that electron affinity is directly proportional to electron affinity.

So, generally electron affinity decreases down the group, because the atomic size increases and with the increase in atomic size, the distance between the nucleus and the outermost shell of an atom increases. This results in low effective nuclear charge and due to less attraction or affinity of the upcoming electron towards the nucleus, makes it difficult to add an electron to such an atom and results in less effective nuclear charge.
Electron affinity increases along the period, because the atomic size decreases along the period from going left to right and due to which distance between the nucleus and the outermost shell decreases. Which results in high value of effective nuclear charge and due to which upcoming electrons show high attraction and it becomes easier to add electrons to such atoms, and results in higher value of electron affinity.
Now coming to the question, as we have already seen; Br has the lowest electron affinity because of high atomic size and therefore has less tendency to accept electrons to form anion whereas Cl has highest electron affinity because of less atomic size and has high tendency to accept electrons. F exceptionally has low electron affinity than Cl but higher than Br because of the very small size of F there is repulsion between inner and outer electrons.
Therefore, the correct order of electron affinity is Cl > F > Br. Hence, option C is the required answer.

Note: You should know that mercury has the lowest electron affinity. As we know metals have a tendency to lose electrons, metals would certainly be the most reluctant in gaining any electrons. Therefore, metals have lowest electron affinity.