Question

Which of the following pairs have nearly identical values of bond energy?

• A. $O_2$ and $H_2$
• B. $N_2$ and $CO$
• C. $F_2$ and $I_2$
• D. $O_2$ and $C{l}_2$

Answer 1

The correct option is C $F_2$ and $I_2$

A) Molecules Bond energy (KJ/mol)

$O=O$ $498$

$H-H$ $436$

$H-H$ bond energy is very high, comparable to the bond dissociation energy of $O_2$, because $H-H$ bond is formed by is orbital of $H$ atoms.

B) Molecules Bond energy (KJ/mol)

$N\equiv N$ $945$

$\stackrel{-}{C}\equiv \stackrel{+}{O}$ $1072$

$N\equiv N$ bond is comparably weaker than $C=O$ bond due to presence of lone pair - lone pair repulsion resided on $N$ atom.

C) Molecules Bond energy (KJ/mol)

$F-F$ $156$

$I-I$ $151$

The atomic radius of $F$ atom is so small that the electrostatic repulsion between nuclei is significant and non-bonding electrons of $F$ atoms repel each other. As a result $F-F$ bond energy is almost identical with bond energy of $I-I$ which is weaker due to formation of bond by $sp$ orbital of $I$ atom.

D) bond energy of $O_2$ ($498$ KJ/mol) is higher than that of ${Cl}_2$ ($243$ KJ/mol) because of double and single bond character of $O_2$ and ${Cl}_2$ respectively.

Correct pair will be (C) $F_2$ and $I_2$.