Question

The electron gain enthalpy (in kJ/mol) of Fluorine, Chlorine, Bromine, and Iodine, respectively, are:

• A. -333, -325, -349 and -296
• B. -333, -349, -325 and -296
• C. -296, -325, -333 and -349
• D. -349, -333, -325 and -296

Answer 1

The correct option is B

-333, -349, -325 and -296

Explanation of the correct option:

The correct answer is option B:

1. Fluorine ($\mathrm{F}$) has a smaller size than Chlorine ($\mathrm{Cl}$) and thus has a less negative electron gain enthalpy.
2. In $\mathrm{F}$, the extra electron will be added to the 2p orbital, but in $\mathrm{Cl}$, it will go into the 3p orbital.
3. A 2p orbital will be more compact because electron-electron repulsion will be greater since it takes up less space than a 3p orbital.
4. Hence in the event of a $\mathrm{F}$, the incoming electron would be accepted with substantially less.
5. Therefore, $\mathrm{F}$'s electron gain enthalpy is lower than $\mathrm{Cl}$'s.
6. Electron gain enthalpy falls when you move from $\mathrm{Cl}$ to Iodine ($\mathrm{I}$) due to a drop in electronegativity.
7. $\mathrm{Cl}>\mathrm{F}>\mathrm{Br}>\mathrm{I}$ is the order of electron gain enthalpy.
8. So, -333, -349, -325, and -296 are the respective electron gain enthalpies of Fluorine, Chlorine, Bromine, and Iodine.

Explanation of the correct options:

Option A:

1. The correct order of electron gain enthalpy is $\mathrm{Cl}>\mathrm{F}>\mathrm{Br}>\mathrm{I}$.
2. Thus, -333, -325, -349, and -296 are not the respective electron gain enthalpies of Fluorine, Chlorine, Bromine, and Iodine.

Option C:

1. The correct order of electron gain enthalpy is $\mathrm{Cl}>\mathrm{F}>\mathrm{Br}>\mathrm{I}$.
2. Thus, -296, -325, -333, and -349 are not the respective electron gain enthalpies of Fluorine, Chlorine, Bromine, and Iodine.

Option D:

1. The correct order of electron gain enthalpy is $\mathrm{Cl}>\mathrm{F}>\mathrm{Br}>\mathrm{I}$.
2. Thus, -349, -333, -325, and -296 are not the respective electron gain enthalpies of Fluorine, Chlorine, Bromine, and Iodine.

Hence, option B is correct, i.e., -333, -349, -325 and -296.