A hydrocarbon is a compound that contains carbon and hydrogen atoms only. Methane CH4, hexane C6H14 and ethene C2H4 are all hydrocarbons.Hydrocarbon families include the alkanes, the alkenes, cycloalkanes and arenes such as benzene. Crude oil is a mixture of hydrocarbons and is the main source of fuels.Carbon and hydrogen have similar electronegativities, so the C-H bond is non-polar. Hydrocarbon molecules are held together only by London (instantaneous dipole-induced dipole) forces.Because they are non-polar, hydrocarbons do not form hydrogen bonds and are insoluble in water. Their boiling points increase as the chain gets longer.