Question

Among halogens, the correct order of amount of energy released in electron gain is?

• A. $\mathrm{F}>\mathrm{Cl}>\mathrm{Br}>\mathrm{I}$
• B. $\mathrm{F}<\mathrm{Cl}>\mathrm{Br}>\mathrm{I}$
• C. $\mathrm{F}>\mathrm{Br}>\mathrm{Cl}>\mathrm{I}$
• D. $\mathrm{I}>\mathrm{Cl}>\mathrm{Br}>\mathrm{F}$

Answer 1

The correct option is B

$\mathrm{F}<\mathrm{Cl}>\mathrm{Br}>\mathrm{I}$

Explanation for the correct option

Option B: $\mathrm{F}<\mathrm{Cl}>\mathrm{Br}>\mathrm{I}$

Electron gain enthalpy

• Electron gain enthalpy is defined as the amount of energy released when an electron is added to an isolated gaseous atom.

Electron gain enthalpy down the group

• As we move down a group the atomic size increases.
• Electron gain enthalpy becomes less negative on moving down a group due to increase in atomic size.
• However, the electron gain enthalpy of $\mathrm{F}$ is less negative than that of $\mathrm{Cl}$ due to electron-electron repulsion in small-sized $\mathrm{F}$ atom.
• Hence, the correct order is $\mathrm{F}<\mathrm{Cl}>\mathrm{Br}>\mathrm{I}$.
• Hence this option is correct.

Hence, option B: $\mathrm{F}<\mathrm{Cl}>\mathrm{Br}>\mathrm{I}$ is the correct answer.