Question

Among halogens, the correct order of amount of energy released in electron gain (electron gain enthalpy) is:

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

Answer 1

The correct option is C $F<Cl>Br>I$

Electron gain enthalpy:

It is the amount of energy released/absorbed when an electron is added to an isolated gaseous atom or ion.

When we go from left to right in a period then electron affinity increases. It is due to increase in number of protons in the nucleus (effective nuclear charge increases) and so attraction of electron increases.

When we go down in a group then the affinity for electron decreases due to the addition of shell and increase in size.

Fluorine is the smallest element of the halogen’s family. The electron gain enthalpy of fluorine is less than chlorine because the size of fluorine is less and the electron density around the nucleus in fluorine is greater than that of chlorine that is why gaining an electron in fluorine experiences more repulsion than chlorine.

Therefore, the order of electron enthalpy of halogens is given by $F<Cl>Br>I$

Hence, option (C) is correct.