Chapter 9, Problem 9.5QE

(a)

Interpretation Introduction

Interpretation:

The reason behind greater lattice energy of $\text{NaI}$ than $\text{KI}$ has to be determined.

Concept Introduction:

The magnitude of the lattice energy for any given ionic solid is determined by equation written as follows:

    $E=\frac{k{Q}_1{Q}_2}{r}$

Here,

$k$ is a constant.

$Q_1$ and $Q_2$ are the charges on the two particles.

 $r$ is the distance of separation in the compound.

$E$ is the lattice energy.

Energy is released if the particles come together and have opposite charges. It is an exothermic process. Energy is absorbed if the sign of charges is same on the particles. It is an endothermic process.

The two main factors responsible for the magnitude of the lattice energy are the charge and radius of the bonded ions. The effect of those factors is as follows:

1. If the charge of the ions increases, the lattice energy increases.

2. If the size of the ions increases, the lattice energy decreases.

If charges are constant, the lattice energies for ionic solids that consist of smaller ions are higher than those of larger ions. The smaller the ionic radii, the closer the ions are to each other and hence the larger the attractive force between the ions.

(b)

Interpretation Introduction

Interpretation:

The reason behind greater lattice energy of ${\text{MgCl}}_2$ than $\text{NaCl}$ has to be determined.

Concept Introduction:

Refer to part (a).