Chapter 9.2, Problem 9.2BFP

Interpretation Introduction

Interpretation:

The compound that has the smaller lattice energy has to be explained using ionic properties.

Concept Introduction:

Formation of ions:

Atom possesses equal number of protons and electrons and remains electrically neutral. By gaining (accepting electrons) or losing (donating electrons) one or more electrons, convert the neutral atom into a charged particle called IONS.

Ionic solids:

Solid ionic compounds are characterized by strong intermolecular force of attraction between the oppositely charged particles and least intermolecular distance. The arrangement of ions is in regular pattern and due to this strong force, exhibits definite shape and volumes.

Lattice energy: The lattice energy ${\text{ΔH}}_{\text{lattice}}^{\text{o}}$ is the enthalpy change of 1 mol of ionic solid separating into gaseous ions.

Periodic trends in lattice energy: The lattice energy results from electrostatic interactions that depend on the ionic size, ionic charge, and the arrangement of ions in solid.

Effect of ionic size: As moving down the periodic table, the size increases (ionic radius) thus the electrostatic energy between cation and anion decreases. So lattice energy decreases as well.

Effect of ionic charge: Across the period, the ionic size decreases and ionic charge increases; hence, the electrostatic attraction increases between cation and anion. Lattice energy increases for the doubly charged ions $\left({\text{Mg}}^{\text{2+}}{\text{O}}^{\text{2-}}\right)$ than the singly charged ions $\left({\text{Li}}^{\text{+}}{\text{F}}^{\text{-}}\right)$.