Chapter 9, Problem 9.32P

Interpretation Introduction

Interpretation:

The relationship between the hardness and magnitude of lattice energy of aluminium oxide is to be explained. Whether the hardness of aluminium oxide can be predicted from its formula is to be determined.

Concept introduction:

Lattice energy is the amount of energy released when the ions combine to form an ionic compound. It is determined to measure the strength of the ionic interactions present in the lattice. A high negative value of lattice energy is the reason behind the formation of ionic compounds.

The lattice energy of compounds depends upon generally three factors as follows:

1. Ionic Size

2. Ionic Charge

3. Arrangement of ions in the lattice

Lattice energy depends upon the electrostatic interaction between the ions present in the lattice. Therefore, lattice energy decreases with the increase in ionic size and decrease in the ionic charge. The expression of electrostatic energy is as follows:

$\text{Electrostatic energy}\propto \frac{\left(\text{Cation charge}\times \text{Anion charge}\right)}{\left(\text{Cation radius}+\text{anion radius}\right)}$