First slide

Electronic configuration and Atomic , physical properties

Question

Which one of the following order is correct for the bond dissociation enthalpy of halogen molecules?

Moderate

A

${Br}_{2} > I_{2} > F_{2} > {Cl}_{2}$
B

$F_{2} > C I_{2} > B r_{2} > I_{2}$
C

$I_{2} > B r_{2} > {Cl}_{2} > F_{2}$
D

$C I_{2} > B r_{2} > F_{2} > I_{2}$

Solution

Enthalpy of dissociation decreases as the bond distance increases from $F_{2}$ to $I_{2}$ due to increase in size of the atom as we move down the group. Due to electron-electron repulsions between the lone pairs in small sized F atoms, the bond dissociation enthalpy of $F_{2}$ is, however, smaller than that of $C l_{2}$ and even smaller than that of $B r_{2}$ Thus, the order of bond dissociation enthalpy is
${Cl}_{2} > {Br}_{2} > F_{2} > I_{2}$

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