Question

The correct order of electron gain enthalpy with negative sign of $F, Cl, Br$, and $I$, having atomic number $9,17,35$ and $53$ respectively, is

• A. $F>Cl>Br>I$
• B. $Cl>F>Br>I$
• C. $Br>Cl>I>F$
• D. $I>Br>Cl>F$

Answer 1

Answer: (B)

$Cl>F>Br>I$

Answer 2

The correct order of electron gain enthalpy with negative sign of $F, Cl, Br$, and $I$ is $Cl>F>Br>I$ Actually halogens have maximum electron gain enthalpy in the corresponding periods and it becomes less negative down the group. However, the negative electron gain enthalpy of fluorine is less than that of chlorine. It is due to the small size of fluorine atom. As a result, there are strong inter electronic repulsions in the relatively small $2p$-orbitals of fluorine and thus, the incoming electron does not experience much attraction.