Haloalkanes display higher boiling points than the corresponding alkanes. This is experimental evidence of the carbon-halogen bond polarization that makes molecules strongly attract one another by dipole-dipole forces, not possible in alkanes.
Going down the Periodic Table within the halogen group, boiling points of the corresponding haloalkenes increase because halogen atomic weight, size and polarizability increase, the London forces thus getting stronger.While many organic compounds are miscible with water and lighter than it, alkyl ahalides are usually non-miscible and denser than water. They go under the latter when mixed.
