Chapter 9, Problem 5ALQ

Interpretation Introduction

Interpretation:

• When a substance changes from a solid to a liquid or from a liquid to a gas whether intermolecular forces changes or not has to be analyzed and explained.

• The reason for a substance to undergo phase change has to be identified.

Concept introduction:

• Matter exists in three distinct physical forms – solid, liquid and gas. There are two types of interactions present in matter – intramolecular meaning, “within the molecule” and intermolecular meaning “between the molecules”.

• Intramolecular force refers to the type of bonding that holds the atoms or ions together to form a stable molecule. Intermolecular force refers to the type of interaction that exists between the so formed molecules by bonding. 

• The nature and strength of the intermolecular forces varies in solids, liquids and gases. The classification of intermolecular force is summarized as follows –

                                               

                                                                 Figure 1

There are three types of intermolecular forces - London dispersion forces, dipole-dipole forces and hydrogen bonding. These forces are collectively known as Van der Waals forces. London dispersion forces exist in non-polar covalent compounds. Dipole-dipole forces present in polar covalent compounds. Hydrogen bonding is formed in polar covalent compounds containing Hydrogen and other high electronegativity like Fluorine, Oxygen or Nitrogen. It is relatively the strongest one.