Chapter 9, Problem 9.28QE

(a)

Interpretation Introduction

Interpretation:

The formulas of the ionic compounds that will form from the pairs of elements potassium and sulfur, potassium and chlorine have to be determined. Also, the pair among potassium and sulfur, potassium and chlorine that has the greater lattice energy has to be explained.

Concept Introduction:

Lattice energy is used to determine the bond strength in ionic compounds. It is the heat of formation for ions of opposite charge in the gaseous phase combine to form an ionic solid.

Lattice energy is the energy required to separate a mole of an ionic solid into gaseous ions. It cannot be measured empirically but it can be estimated by the Born-Haber cycle.

  $\text{MX}\left(\text{s}\right)\to {\text{M}}^{+}\left(\text{g}\right)+{\text{X}}^{-}\left(\text{g}\right)$

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.

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 their distance of separation in the compound.

$E$ is the lattice energy.

(b)

Interpretation Introduction

Interpretation:

The formulas of the ionic compounds that will form from the pairs of elements lithium and fluorine, rubidium and chlorine have to be determined. Also, the pair among potassium and sulfur, potassium and chlorine that has the greater lattice energy has to be explained.

Concept Introduction:

Refer to part (a).