Chapter 7, Problem 65A

Interpretation Introduction

Interpretation:

The effect of change in size of ion on the lattice energy needs to be explained.

Concept introduction:

Ionic bonds are formed when there is complete transfer of electrons from one atom to another. Here the atoms either lose or gain electrons so as to form negatively or positively charged ions. Due to its interaction, there is forces of attraction between these ions resulting in ionic bond and hence forth ionic crystals.

Answer to Problem 65A

The increase in size of ion results in distance between the outermost electron and central nucleus causing decreased lattice energy.

Explanation of Solution

Atoms convert to ions by losing electron or gaining electrons. The ions that are formed have positive or negative charges on them. The ions are arranged in such a way that oppositely charged ions are placed next to each other such that their total charge is zero. As the bonds are held by electrostatic force of attraction, the compounds have its ions held at lattice points and is mostly crystalline. The energy that is released during the process of formation of ionic compound is lattice energy.

Consider two ions ${\text{X}}^{+}$ and ${\text{Y}}^{-}$ which on combination releases lattice energy.

${\text{X}}^{+}+{\text{Y}}^{-}\to {\text{X}}^{+}{\text{Y}}^{-}+\text{Lattice energy}$

If the radius of the ion increases, the lattice energy decreases. This is due to the fact that as the size of ion increases, distance between the outermost electrons and the central nucleus increases reducing the force of attraction and hence can be easily removed. This results in the decrease in lattice energy.

Conclusion

The increase in size of ion results in distance between the outermost electron and central nucleus causing decreased lattice energy.