Physical Properties

The boiling point of a halogenoalkane depends mainly on the strength of the van der Waals forces between its molecules. There are also permanent dipole-dipole forces because the carbon-halogen bond is polar.Boiling point increases as the carbon chain gets longer, because larger molecules have more electrons and a greater surface area of contact, so the van der Waals forces are stronger.For the same carbon chain, boiling point increases from chloro to bromo to iodo compounds. The larger halogen atom has more electrons, so the van der Waals forces increase even though the bond becomes less polar.Branched isomers have lower boiling points than straight-chain isomers because the molecules cannot pack as closely together.Halogenoalkanes are insoluble in water because they cannot form hydrogen bonds with water molecules. They mix well with other organic solvents. Chloromethane is a gas at room temperature but most other halogenoalkanes are liquids.