Notice how the cations and anions are arranged? The electrostatic forces of attraction between oppositely charged ions is very strong!
Properties of ionic compounds
- Crystalline solids
- High m.p and b.p Large amount of thermal energy needed to break strong electrostatic forces of attraction between oppositely charged ions. Note: the larger the charges of the positive and negative ions, the stronger the ionic bonds. Ionic compounds are usually used as refractory materials.
- Low volatilities Cannot evaporate easily because of the strong electrostatic forces of attraction. Note: Volatility is inversely proportional to b.p. => High b.p ; Low volatility. Vice versa.
- Conduct electricity in aq. and molten states Free moving ions. Can carry current. Note: in solid state, ions are held in fixed positions, hence cannot conduct electricity.
- Mostly soluble in water
A large number of water molecules. Between molecules: Van Der Waals forces of attraction (weak). Within molecules: covalent bond (strong)
Properties of covalent compounds
- Boiling points Low mp and bp. Weak intermolecular forces of attraction (Van Der Waals?) between molecules, hence little energy needed to overcome. Note: the intramolecular bonds (covalent bonds) are very strong. This is DIFFERENT from the intermolecular forces of attraction.
- Volatility High volatility ? Evaporate easily. Weak VDW forces between molecules. Diffuse easily.
- Solubility Mostly insoluble in water, soluble in organic solvents. Note: there are exceptions. Hydrogen chloride, glucose and ammonia are covalent compounds but are highly soluble in water.
- Lack of electrical conductivity. Simple covalent molecules DO NOT conduct electricity in any state. Note: exception is graphite. It conducts electricity.