KEY2CHEM

Structure of Ionic Solids

Ionic solids are composed of regular arrangements of oppositely-charged ions repeating in three dimensions. Ions of opposite charges are held together by electrostatic attractions; the magnitude of the force of these attractions is predicted by Coulomb’s law.

$$F \propto \frac{q_1 \times q_2}{r^2}$$

An increase in the magnitude of ion charges increases the force holding the ions together. Similarly, a decrease in the distance separating ions increases the force holding the ions together.

Example 1.

Which best represents the structure of an ionic solid?

A.

B.

C.

Solution

C.

Ionic solids are composed of arrays of regularly-repeating ions of opposing charges. The ions align to maximize attractive interactions between opposite charges and minimize repulsions between like charges.

Example 2.

Which ionic solid is expected to have the strongest attractive interactions between its ions?

A. $$\require{mhchem}\ce{NaCl}$$

B. $$\require{mhchem}\ce{LiF}$$

C. $$\require{mhchem}\ce{MgO}$$

Solution

C. $$\require{mhchem}\ce{MgO}$$

The attractive force between ions in an ionic solid is described by Coulomb’s law ($$F \propto \frac{q_1 \times q_2}{r^2}$$). Increasing ion charge and decreasing ion size (distance separating ions) leads to increased attractive interaction.

Example 3.

Which pair of ions is expected to have the strongest electrostatic attraction?

A.

B.

C.

Solution

A.

As described by Coulomb’s law, electrostatic attraction increases with increasing ion charge and decreases with increasing ion size.