Properties of ionic compounds

The physical properties of ionic compounds can be explained by their giant ionic lattice structure and ionic bonds.

Melting points

Ionic compounds are held together by many strong electrostatic forces between the oppositely charged ions. A lot of energy is needed to overcome these ionic bonds, so ionic compounds have high melting points.

Ionic bonds between Mg2+ and O2- ions are stronger than those between Na+ and Cl- ions so the melting point of MgO is higher.
Ionic compoundMelting point
NaCl801°C
MgO2,852°C
curriculum-key-fact
Ionic compounds have high melting points and are therefore in the solid state at room temperature.

Conduction of electricity

A substance can conduct electricity if:

  • it contains charged particles, and
  • these particles are free to move from place to place

Ionic compounds conduct electricity when molten (liquid) or in aqueous solution (dissolved in water), because their ions are free to move from place to place. Ionic compounds cannot conduct electricity when solid, as their ions are held in fixed positions and cannot move.

curriculum-key-fact
Ionic compounds are conductors of electricity when molten or in solution, and insulators when solid.

Solubility

Not all ionic substances are soluble and some are more soluble than others.

When an ionic compound is added to water and dissolves it separates into its separate ions. The ions are surrounded by water molecules.

Although a water molecule is neutral overall, it has a weak positive charge near its hydrogen atoms, and a weak negative charge near its oxygen atom. Water molecules surround the ions in solution because they are attracted by the charges of the ions.

Move on to Test
next