Question

Chlorine has ______ electron affinity than fluorine.

Answer 1

• The quantity of energy released when the isolated and neutral atom in the gaseous phase form negatively charged species (anion) by the gain of one electron is termed as electron affinity. The general equation for electron affinity of element X is:

$\mathrm{X}\left(\mathrm{g}\right)+{\mathrm{e}}^{-}\to {\mathrm{X}}^{-}\left(\mathrm{g}\right)$

• Electron affinity relies on two factors, atomic size, and nuclear charge.
• The effective nuclear charge and atomic size both increase on moving top to bottom in the Group. Due to a more significant increase in atomic size, the addition of electrons becomes easy and therefore, the electron affinity decreases down the Group in the periodic table.
• Fluorine (F) and Chlorine (Cl) both belong to the same group (Group 17) but Fluorine lies above Chlorine in the group. Therefore, Fluorine is smaller than Chlorine as the atomic size increases down the Group.
• Due to the larger size of Chlorine than Fluorine, the electron density per unit volume of Fluoride ion (F^-) is higher than Chloride (Cl^-) ion. Therefore, the tendency of Fluorine to accept the electron decreases, and therefore, the electron affinity of Chlorine is more than Fluorine.

$$\begin{gathered} \mathrm{F}\left(\mathrm{g}\right)+{\mathrm{e}}^{-}\to \underset{\mathrm{Fluoride}\mathrm{ion}}{{\mathrm{F}}^{-}\left(\mathrm{g}\right)} \\ \mathrm{Cl}\left(\mathrm{g}\right)+{\mathrm{e}}^{-}\to \underset{\mathrm{Chloride}\mathrm{ion}}{{\mathrm{Cl}}^{-}\left(\mathrm{g}\right)} \end{gathered}$$

• Hence, Chlorine has more electron affinity than Fluorine.