The compounds made up of only carbon and hydrogen are called hydrocarbons. They are obtained mainly from petroleum, natural gas and coal.

Hydrocarbons are broadly classified into two main categories - aliphatic and aromatic The aliphatic hydrocarbons are further classified as saturated (alkanes), unsaturated (alkenes and alkynes) and alicyclic (cycloalkanes) hydrocarbons.

Alkanes are the simplest class of organic compounds.

They are made of carbon and hydrogen atoms only and contain two types of bonds, carbon-hydrogen (C—H) and carbon-carbon (C—C) single covalent bonds. They do not have functional groups. Alkanes form a homologous series with the general formula CnH2n + 2, where n is the number of carbon atoms in the molecule. Alkanes are also known as the saturated hydrocarbons as all the four single covalent bonds of each carbon in their molecules are fully satisfied or 'saturated.' These hydrocarbons are relatively unreactive under ordinary laboratory conditions, but can be forced to undergo reactions under drastic conditions. It is for this reason that they are called paraffins (Latin, parum affinis = little activity).

Each carbon atom in alkanes is sp3 hybridized. The four sp3 hybrid orbitals are used in making four sigma bonds giving a tetrahedral structure.

Alkanes exhibit chain isomerism. The first three hydrocarbons of the series viz., methane, ethane and propane do not exhibit isomerism. All higher hydrocarbons show chain isomerism and the number of isomers goes on increasing rapidly with the increase in the number of carbon atoms.