The order of electron gain enthalpy in $\mathrm{kJ} / \mathrm{mol}$ of fluorine, chlorine, bromine and iodine, respectively are

JEE Main · 2020 · 07 Jan 2020 · Shift 1 · Classification of Elements and Periodicity

The order of 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✓ Correct
(C)-349, -333, -325 and -296
(D)-296, -325, -333 and -349

Answer: (B)

Solution

Electron gain enthalpy generally grows less negative down the halogens as size increases, but fluorine breaks the trend: its very small

2 p

shell crowds the incoming electron, making its value less negative than chlorine's. The magnitudes thus place chlorine highest, then fluorine, then bromine, then iodine, so for F, Cl, Br, I respectively the values run

- 333, - 349, - 325, - 296 kJ/mol

JEE Main · 2020 · 07 Jan 2020 · Shift 1 · Single correct option

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