Stronger bonding = requires more energy to break the (intermolecular) forces (or 'bonds' at GCSE) = higher melting points
- Ionic compounds have strong ionic bonds (electrostatic attraction); so high melting point
- Macromolecular covalent compounds have strong covalent bonds; so high melting point
- Simple covalent compounds have weak intermolecular 'bonds' so require less energy than macromolecular compounds
- Metals have strong metallic bonds (electrostatic attraction); so high melting points
Solubility - ionic compounds can dissolve in water. The structure of the ionic lattice made up of opposite charged ions, allows them to be "attracted" to the water molecules.
Also, ionic compounds are brittle because of their arrangement of ions.
For other properties e.g. conductivity, BBC Bitesize is very good at GCSE for explaining that.