Chapter 7, Problem 7.38QP

(a)

Interpretation Introduction

Interpretation:

The higher boiling point of ${\text{NH}}_{\text{3}}$ as compared to ${\text{CH}}_4$ and the higher melting point of $\text{KCl}$ as compared to ${\text{I}}_{\text{2}}$ should be explained on the basis of intermolecular forces.

Concept introduction:

• Polarity of a bond is due to the difference in electro-negativities of atoms presented in it. The polarities of bonds are represented by using vectors.
• If the result of all bond polarities or vector sum is non-zero in a molecule, then the molecule is called as polar molecule.
• If the result of all bond polarities or vector sum is zero in a molecule, then the molecule is called as nonpolar molecule.
• Intermolecular force is the set of repulsive and attractive forces between molecules that result from the polarity between neighboring molecules. There are four types of intermolecular forces.
• Dipole – Dipole interaction: This force takes place between polar compounds.
• Hydrogen bonding is a type of dipole-dipole interaction of molecules when the hydrogen is bonded to strong electronegative atom (F, O, N, etc) in the molecules.
• Dispersion force is a weak force and this force is present in all compounds force.
• Boiling point depends upon the strength of inter molecular forces. 
• Melting point depends upon the strength of inter molecular forces. 

(b)

Interpretation Introduction

Interpretation:

The higher boiling point of ${\text{NH}}_3$ as compared to ${\text{CH}}_4$ and the higher melting point of $\text{KCl}$ as compared to ${\text{I}}_{\text{2}}$ should be explained on the basis of intermolecular forces.

Concept introduction:

• Polarity of a bond is due to the difference in electro-negativities of atoms presented in it. The polarities of bonds are represented by using vectors.
• If the result of all bond polarities or vector sum is non-zero in a molecule, then the molecule is called as polar molecule.
• If the result of all bond polarities or vector sum is zero in a molecule, then the molecule is called as nonpolar molecule.
• Intermolecular force is the set of repulsive and attractive forces between molecules that result from the polarity between neighboring molecules. There are four types of intermolecular forces.
• Dipole – Dipole interaction: This force takes place between polar compounds.
• Hydrogen bonding is a type of dipole-dipole interaction of molecules when the hydrogen is bonded to strong electronegative atom (F, O, N, etc) in the molecules.
• Dispersion force is a weak force and this force is present in all compounds force.
• Boiling point depends upon the strength of inter molecular forces. 
• Melting point depends upon the strength of inter molecular forces.