Question

The decreasing order of electron affinity of F, Cl and Br is:
A. $\text{Cl > F > Br}$
B. $\text{F > Br > Cl}$
C. $\text{Br > F > Cl}$
D. None of these

Answer 1

Hint: Electron affinity is the ability of an atom to accept electron pair and due to which they yield energy. When we move down the group, the electron affinity decreases due to an increase in the atomic radii.

Complete step by step answer:
- In the given question, we have to identify the correct order of the given halogens according to their electron affinity.
- As we know that energy is released when an electron is added to the atom whereas the energy is needed when we break the bond.
- So, the first electron affinity is always negative as the amount of energy is released by the atom to accept the pair of electrons.
- The affinity to accept a paired electron is based on the atomic radii of the atom.
- Because we know that when we move down the group then the size of the atom increases due to which the attraction between electron and nucleus decreases and due to which the incoming electron will also have less attraction towards the nucleus.
- So, less is the attraction between nucleus and electron less will be the energy released.
- So, among bromine, chlorine and fluorine bromine has the larger size so it will have the smallest value of electron affinity.
- Now, the chlorine will have more electron affinity than the fluorine due to smaller size of fluorine when another electron comes then it repels the electron and hence, there is not much attraction between nucleus and electron.
- So, the correct decreasing order will be: $\text{Cl > F > Br}$
So, the correct answer is “Option A”.

Note: Fluorine is the first element of the halogen group (18 groups) which has many anomalous properties such as smallest size, different electronegativity, etc. Electron affinity can be used to predict the hardness of the compound.