Hydrocarbons are compounds which contain only carbon and hydrogen. The main source of hydrocarbons is petroleum.
The word aliphatic is derived from the Greek word aleiphar meaning fat. Aliphatic hydrocarbons were named so because they were derived from fats and oils.
Hydrocarbons can be acyclic compounds, which are straight chain compounds, or cyclic compounds, which have rings of carbon atoms.
The word aromatic is derived from the word aroma meaning fragrance. The aromatic compounds have a characteristic smell. Structurally, they include benzene and its derivative.
The aliphatic hydrocarbons can be divided into two categories: saturated hydrocarbons and unsaturated hydrocarbons.
In saturated hydrocarbons, carbon atoms are linked to each other by single bonds whereas in unsaturated hydrocarbons, multiple bond (double and triple bonds) are present between carbon atoms.