Linear and branched 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.