Chapter 14, Problem 1STP

Interpretation Introduction

Interpretation: To match the correct pair of molecule with strongest intermolecular force of interaction.

Concept introduction:

The forces that exist among non-polar molecules are called London dispersion forces. Atoms can develop a temporary dipolar arrangement of charge on movement of electrons around the nucleus. This instantaneous dipole induces a same dipole in a neighboring atom.

Ion-ion force of attraction is present between two oppositely charged ions namely cations and anions. Ionic bonds can be formed by transfer of one or more electrons from one atom to the other to complete the octet.

Answer to Problem 1STP

Option C is correct.

Explanation of Solution

${\text{Li}}_{\text{2}}\text{O}$ is a solid and composed of positively charged ${\text{Li}}^{\text{+}}$ cation and negatively charged ${\text{O}}^{\text{2-}}$ anion arranged in definite pattern. One valence electron from each of the two $\text{Li}$ atoms is transferred to one $\text{O}$ atom. Thus oxygen completes its octet. So, in ${\text{Li}}_{\text{2}}\text{O}$ predominant force is ion-ion.

${\text{F}}_{\text{2}}$ is non-polar homo-diatomic molecule so only intermolecular force that is operated in it is London dispersion forces.

${\text{SO}}_{\text{2}}$ is bent shaped and hence it possesses dipole moment. Due to higher electronegativity of oxygen it acquires partial negative and sulfur acquires partial positive charge. Hence dipole-dipole force is operated in ${\text{SO}}_{\text{2}}$ predominantly.

Conclusion

${\text{F}}_{\text{2}}$ cannot for dipole-dipole force because of zero dipole moment of ${\text{F}}_{\text{2}}$ . London dispersion force is present in every molecule whether polar or non-polar. ${\text{SO}}_{\text{2}}$ and ${\text{Li}}_{\text{2}}\text{O}$ also have London dispersion forces but it is not predominant force in them.

Hence other options are wrong.