Alkanes are organic compounds made up of carbon and hydrogen only and all carbon-carbon bonds are single bonds in alkane. Alkanes that does not possess ring-structure are acyclic alkanes. The general formula of alkanes is
where n is number of carbon atoms.
Hydrogens that are bonded to primary carbon that is a carbon which is bonded only to one carbon atom is known as primary hydrogen.
The structure of the acyclic alkane(s) that have 8 carbons and only primary hydrogens is shown in the image.