Ionic compounds have regular structures, called giant ionic lattices. In a giant ionic lattice, there are strong electrostatic forces of attraction acting in all directions between the oppositely charged ions. The structure and bonding of ionic compounds explain their properties.
See the study guide on the three states of matter to see how bonding and structure are related to the properties of substances.
Energy must be transferred to a substance to make it melt or boil. This energy overcomes the strong electrostatic forces of attraction which act in all directions between the oppositely charged ions:
The more energy needed, the higher the melting point or boiling point. Since the electrostatic forces of attraction between oppositely charged ions are strong, their melting and boiling points are high.
Ionic compounds are held together by electrostatic forces between the oppositely charged ions. These forces are usually referred to as ionic bonding. As the ionic lattice contains such a large number of ions, a lot of energy is needed to overcome this ionic bonding so ionic compounds have high melting and boiling points.
The strength of the ionic bonds depends on the charge on the ions. Ions with higher charge will have stronger forces between them, so will need more energy in order to overcome these forces.
|Compound||Melting point||Boiling point|
Ionic bonds between Mg2+ and O2- ions are stronger than those between Na+ and Cl- ions
A substance can conduct electricity if:
An ionic compound can conduct electricity when:
Both these processes allow ions to move from place to place. Ionic compounds cannot conduct electricity in the solid state because their ions are held in fixed positions and cannot move.