Why is Chlorine a gas at room temperature but Sodium Chloride is a solid?

Chlorine is a gas at room temperature due to its structure.  Chlorine is made up of two chlorine atoms, held together by covalent bonds, forming simple covalent molecules.  Whilst the covalent bonds within the chlorine molecules are strong, there are only weak intermolecular forces between molecules, which require very little energy to overcome. Therefore chlorine has a low boiling point and so is a gas at room temperature. In contrast, sodium chloride is a solid at room temperature as it is a giant ionic compound.  The individual sodium and chloride ions are held together by electrostatic forces of attraction between the oppositely charged ions.  These ionic bonds are very strong and are formed in all directions, creating a giant ionic lattice.  Due to the strength of the bonds, large amounts of energy are needed to break them and therefore sodium chloride has a high melting point.