Physical properties

Boiling points. Haloalkanes are polar and heavier than the alkanes they come from, so they boil higher. Three trends:

• The heavier the halogen, the higher the boiling point: for the same alkyl group, R–I > R–Br > R–Cl > R–F. Bigger atoms have bigger electron clouds and stronger van der Waals forces.
• A longer chain raises the boiling point.
• Branching lowers it: a branched molecule is more compact, with less surface to touch its neighbours.

Melting points of dihalobenzenes. The para isomer melts higher than the ortho and meta ones. Its shape is more symmetrical, so its molecules pack neatly into a crystal, and more energy is needed to break them apart.

Solubility. Even though the C–X bond is polar, haloalkanes hardly dissolve in water. To dissolve, a haloalkane would have to break the strong hydrogen bonds between water molecules, and it cannot form hydrogen bonds with water to pay that back. They dissolve well in organic solvents.

Dipole moments. In chlorobenzene the C–Cl bond is shorter and less polar than in a haloalkane: the carbon is sp² (it holds electrons more tightly), and resonance gives the bond some double-bond character. So chlorobenzene has a smaller dipole moment than cyclohexyl chloride.