Structure of Ionic Compounds

Ionic compounds exist as three-dimensional lattice structures. The structure is based around a repeating unit (the formula unit)

The coordination number is used to express the number of ions that surround a given ion in the lattice.

Lattice enthalpy is a measure of the strength of the forces between ions in an ionic solid.

It depends on…

1. ionic radius (smaller radius, stronger attraction)

2. charge of ions (higher charger, stronger attraction

The physical properties of ionic compounds reflect their lattice structure

Melting and Boiling Points

Ionic compounds tend to have high melting and boiling points due to the strength of the electrostatic attractions between the ions in the lattice.

The melting and boiling points are generally higher when the charge on the ions is greater.

Volatility

the tendency of a substance to vaporize

• Substances with high volatility are more likely to exist as a vapor

• Ionic bonds are very strong, require large amounts of energy to overcome

• At room temperature, ions do not have enough energy to break away

• ionic compounds have no odour

Solubility

the ease with which a solid (the solute) becomes dispersed through a liquid (the solvent) to form a solution.

Dissolving in water involves the attraction of polar water molecules to the oppositely- charged ions in the ionic lattice, and the hydration of the separated ions

Electrical Conductivity

Two things are needed for electrical conductivity

1. Presence of charged particles

2. Charged particles must be free to move

Solid Ionic Lattice

No conduction because no freely moving charged particles, ions are

locked into position