Ionic Compounds
Notice how the cations and anions are arranged? The electrostatic forces of attraction between oppositely charged ions is very strong!
Sodium Chloride dot and cross diagram
Properties of ionic compounds
- Crystalline solids
- Hard
- 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
Covalent Compounds
Water molecules - covalent bonds & intermolecular forces of attraction
Dot and cross diagram of 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.