Question

Compare the bond energies of $F-F$ and $Cl-Cl$ . State the reason also.

Answer 1

Hint: $F-F$ means the bond energy of fluorine atoms and $Cl-Cl$ means the bond energy of chlorine atoms. Both the elements belong to the same group, i.e., group 17. We know that the size of the atoms increases down the group, which can be related to the bond energy.

Complete step-by-step answer:Bond energy means the amount of energy required to break the bond between the atoms. There are many other names of the bond energy like bond-dissociation enthalpy, bond strength, etc. If the amount of the bond energy of a compound is high then the bonds between the elements in the compound are strong, if the amount of the bond energy of a compound is low then the bonds between the elements in the compounds are weak.
$F-F$ means the bond energy of fluorine atoms and $Cl-Cl$ means the bond energy of chlorine atoms. Both the elements belong to the same group, i.e., group 17. As we know that the size of the atoms increases down the group, so the bond length also increases down, which means the bond strength decreases. From this, the bond energy of fluorine must be higher than that of chlorine. But this is not true. The bond energy of chlorine is more than the bond energy of fluorine.
This is due to the fact that the size of the fluorine atoms is very small, and the electrons on the fluorine atom repel each other due to which the bonds become weaker and the bond energy decreases. Since the chlorine atom is more than the fluorine, the repulsion in chlorine will be much lower.

Note:The bond energy or bond-dissociation energy of the fluorine is even lesser than the bromine atom of the same group. The repulsion in the fluorine atoms is very high.