1. Explaining the Physical Properties of Ionic Substances

2. Explanation of melting points
State is determined by how close particles (atoms/molecules/ions) are to each other.
To change state from a solid to a liquid, you must separate the particles by breaking the bonds/forces between them.
If these bonds/forces are weak, only a low energy is required to break them and the substance will have a LOW melting point.
If these bonds/forces are strong, a high energy is required and the substance will have a HIGH melting point.

3. Melting points in Ionic Compounds
Ionic compounds have a molecular / lattice / network structure: + -
Ionic bonds
To separate ions, IONIC / COVALENT BONDS must be broken.
These are very strong / weak and so require low / high energy to break them.
Because of this, the melting point of ionic compounds is usually very high / low.

4. Conductivity
A substance can conduct electricity if there is a free movement of charged particles (electrons or ions).
Metals
In metals, some electrons have broken free of their atoms and are able to move freely amongst the atoms. This arrangement is like a number of islands (atoms) in a sea (of electrons).
Because there are charged particles (ELECTRONS) which are free to move, all metals conduct electricity in any state.

5. Conductivity in Ionic Compounds
Ionic substances are made up of charged particles – atoms / ions.
However, in the SOLID state these are NOT able to move freely because they are held together very strongly by ionic / covalent bonds.
When melted or dissolved, many of these ionic / covalent bonds have broken and as a result the IONS ARE FREE TO MOVE.
LIQUID ionic compounds and SOLUTIONS of ionic compounds CAN therefore conduct electricity. + - + - - + - + - + + + - + -