Question
Which one of the following orders is correct for the bond dissociation enthalpy of halogen molecules?
A.
$$C{l_2} > B{r_2} > {F_2} > {I_2}$$
B.
$$B{r_2} > {I_2} > {F_2} > C{l_2}$$
C.
$${F_2} > C{l_2} > B{r_2} > {I_2}$$
D.
$${I_2} > B{r_2} > C{l_2} > {F_2}$$
Answer :
$$C{l_2} > B{r_2} > {F_2} > {I_2}$$
Solution :
As the size increases, bond dissociation enthalpy becomes lower. Also, as the size of atoms get smaller, ion pairs on the two atoms get close enough together to experience repulsion. In case of $${F_2},$$ this repulsion is bigger and bond becomes weaker.
Hence, the correct order is $$C{l_2} > B{r_2} > {F_2} > {I_2}.$$