Chapter 10, Problem 10.17QP

(a)

Interpretation Introduction

Interpretation:

The compounds ${\text{H}}_{\text{2}}\text{O}$, ${\text{CH}}_{\text{4}}$, and $\text{LiCl}$ has to be ranked in order of highest to lowest boiling point.

Concept Introduction:

The force of attraction between two molecules that experience a short-lived dipole is known as London Dispersion force.  Large molecules will have large number of electrons.  These electrons when in constant motion develop a temporary dipole.  The formed temporary dipole interacts with other temporary dipoles resulting in an attractive force between the molecules.  Molecules with a very high molar mass have large number of electrons.  This result in having stronger force of attraction and due to this the melting point and boiling point of the molecule will be higher.

Example:  Alkanes that contain one to four carbon atoms are gases, five to seventeen carbon atoms are colorless liquids and more than seventeen carbon atoms are waxy solids.

Ionic substances contain ions.  Covalent substances have covalent bonds that are formed by mutual sharing of electrons.  Ionic substances are made of up of many positive and negative ions that constitute a three-dimensional crystal.  Due to this three-dimensional crystal, ionic substances have higher melting and boiling points than covalent substances.

(b)

Interpretation Introduction

Interpretation:

The compounds ${\text{C}}_{\text{2}}{\text{H}}_{\text{6}}$, ${\text{C}}_{\text{3}}{\text{H}}_{\text{8}}$, and $\text{NaCl}$ has to be ranked in order of highest to lowest boiling point.

Concept Introduction:

Refer part (a).