Chapter 12, Problem 12.51P

(a)

Interpretation Introduction

Interpretation:

The substance among the following pair that has the lower boiling point is to be identified.

$\text{LiCl}$ or $\text{HCl}$

Concept introduction:

Intermolecular forces operate between the molecules so changes with change in the phase and effects with physical properties of the substance. In intermolecular forces, the bond is formed between two molecules with partial charges that are present relatively far away from each other. The types of intermolecular forces are as follows:

1. Ion-dipole: Ion-dipole forces are the attractive forces that exist between an ion and a polar molecule.

2. Hydrogen bond: Hydrogen bonding is the attractive forces that exist between the molecule with a hydrogen atom bonded to an electronegative atom like fluorine, nitrogen, and oxygen of one molecule and an electronegative atom of another molecule.

3. Dipole-dipole: Dipole-dipole is the attractive forces that exist between two polar molecules that have a permanent dipole.

4. Ion-induced dipole: Ion-induced dipole is the attractive forces that exist between the ion and a nonpolar molecule.

5. Dipole-induced dipole: Dipole-induced dipole is the attractive forces that exist between a polar and a nonpolar molecule.

6. Dispersion forces: In dispersion forces, a temporary dipole is generated on one molecule that further induces a temporary dipole on the molecule adjacent to it. The temporary dipole results in the attraction between opposite charges and dispersion forces exist in the molecule. All the atoms and molecules exhibit dispersion forces.

The boiling point of the liquid is defined as the temperature at which the liquid and gas are in equilibrium and the pressure is $1\text{atm}$. The boiling point is directly related to the strength of intermolecular forces. More is the strength of intermolecular forces more will be the boiling point of the compound. The increasing order of strength is as follows:

$\text{dispersion forces}<\text{dipole}-\text{dipole forces}<\text{hydrogen bonds}<\text{ion}-\text{dipole forces}$

An ionic bond is formed by the interaction of a metal with a non-metal. When a metal element interacts with a non-metal, the metal loses electron/electrons. The electrons lost are gained by the nonmetal. The metal turns into a cation whereas the non-metal turns into an anion. The electrostatic force of attraction between the cation and the anion leads to the formation of an ionic bond between the two. The constituents in an ionic compound are ions.

(b)

Interpretation Introduction

Interpretation:

The substance among the following pair that has the lower boiling point is to be identified.

${\text{NH}}_3$ or ${\text{PH}}_3$

Concept introduction:

Intermolecular forces operate between the molecules so changes with change in the phase and effects with physical properties of the substance. In intermolecular forces, the bond is formed between two molecules with partial charges that are present relatively far away from each other. The types of intermolecular forces are as follows:

1. Ion-dipole: Ion-dipole forces are the attractive forces that exist between an ion and a polar molecule.

2. Hydrogen bond: Hydrogen bonding is the attractive forces that exist between the molecule with a hydrogen atom bonded to an electronegative atom like fluorine, nitrogen, and oxygen of one molecule and an electronegative atom of another molecule.

3. Dipole-dipole: Dipole-dipole is the attractive forces that exist between two polar molecules that have a permanent dipole.

4. Ion-induced dipole: Ion-induced dipole is the attractive forces that exist between the ion and a nonpolar molecule.

5. Dipole-induced dipole: Dipole-induced dipole is the attractive forces that exist between a polar and a nonpolar molecule.

6. Dispersion forces: In dispersion forces, a temporary dipole is generated on one molecule that further induces a temporary dipole on the molecule adjacent to it. The temporary dipole results in the attraction between opposite charges and dispersion forces exist in the molecule. All the atoms and molecules exhibit dispersion forces.

The boiling point of the liquid is defined as the temperature at which the liquid and gas are in equilibrium and the pressure is $1\text{atm}$. The boiling point is directly related to the strength of intermolecular forces. More is the strength of intermolecular forces more will be the boiling point of the compound. The increasing order of strength is as follows:

$\text{dispersion forces}<\text{dipole}-\text{dipole forces}<\text{hydrogen bonds}<\text{ion}-\text{dipole forces}$

(c)

Interpretation Introduction

Interpretation:

The substance among the following pair that has the lower boiling point is to be identified.

$\text{Xe}$ or ${\text{I}}_2$

Concept introduction:

Intermolecular forces operate between the molecules so changes with change in the phase and effects with physical properties of the substance. In intermolecular forces, the bond is formed between two molecules with partial charges that are present relatively far away from each other.

Dispersion forces: In dispersion forces, a temporary dipole is generated on one molecule that further induces a temporary dipole on the molecule adjacent to it. The temporary dipole results in the attraction between opposite charges and dispersion forces exist in the molecule. All the atoms and molecules exhibit dispersion forces.

The boiling point of the liquid is defined as the temperature at which the liquid and gas are in equilibrium and the pressure is $1\text{atm}$. The boiling point is directly related to the strength of intermolecular forces. More is the strength of intermolecular forces more will be the boiling point of the compound. The increasing order of strength is as follows:

$\text{dispersion forces}<\text{dipole}-\text{dipole forces}<\text{hydrogen bonds}<\text{ion}-\text{dipole forces}$

The electron cloud around an atom and molecules gets distorted when the external electric field is applied. Polarizability is the measure of that distortion of the electron cloud in the presence of the electric field. This distortion is responsible for the generation of the dipole in nonpolar molecules and leads to dispersion forces.

Polarizability is directly related to size and therefore increases with increase in size. The pi electrons can be easily polarized as compared to sigma electrons and therefore compounds with pi bonds has greater polarizability than compounds with sigma bonds.