AS Chem - Intermolecular forces

1. In terms of the intermolecular forces involved suggest why hydrogen iodide requires more heat energy for melting than hydrogen chloride does.

3.The heat energy needed to vaporise one mole of sodium chloride is much greater than the heat energy required to melt one mole of sodium chloride. Explain why this is so.

4.In terms of its structure and bonding suggest why graphite has a very high melting point.

Iodine is less electronegative, so there will be less distortion in the bond, and the bond will be stronger meaning more energy is needed to break it.

Can anyone help me with the following q's please:

1. In terms of the intermolecular forces involved suggest why hydrogen iodide requires more heat energy for melting than hydrogen chloride does.

2.Explain why the heat energy required to melt sodium chloride is large.

3.The heat energy needed to vaporise one mole of sodium chloride is much greater than the heat energy required to melt one mole of sodium chloride. Explain why this is so.

4.In terms of its structure and bonding suggest why graphite has a very high melting point.

Thanks

2. Sodium chloride has strong (ionic) electrostatic attractions between the cations and anions

3. I think it is harder to vaporise because sodium chloride is soluble in water as it's able to form hydrogen bonds which are the strongest form of intermolecular forces.

4. Graphite has strong covalent bonds as well as the intermolecular forces of instantaneous (or induced) dipole- instantaneous dipole attractions between 'sheets' of carbon atoms.

By the way is instantaneous dipole-dipole attraction the same as van der Waals or not?