Types of alkanes

Alkanes, whose carbons are connected in a continuos chain (no branched) are called straight-chain alkanes.

The family of straight-chain alkanes is an example of  a homologous series. A homologous series of compounds is one in which succesive members differ by one methylene (CH2) group.  The general formula for alkanes homologs is CH3(CH2)nCH3.  Propane (CH3CH2CH3, with n=1) and butane (CH3CH2CH2CH3, with n=2) are homologs.

Alkanes, whose carbon chains branch, are called branched-chain alkanes.

Alkanes are classified as linear, branched, cyclic, and polycyclic. Linear alkanes have a carbon chain without branches. Linear alkanes are ethane, propane, butane, pentane, hexane, heptane...

Branched alkanes are formed by a linear chain, from which substituents (branches) start. An example of a branched alkane is 2-methylpropane, which has a straight chain of three carbons (propane) with a branch (methyl) at position 2.

Cyclic alkanes have chain ends joined by a carbon-carbon bond. They have the molecular formula $C_nH_{2n}$ and contain two fewer hydrogens than the coresponding acyclic alkane. Examples of cyclic alkanes or cycloalkanes are: cyclopropane, cyclobutane, cyclopentane.....

Polycyclic alkanes have several condensed rings. The structure of a bicyclic alkane can be seen in the molecular model.