An alkane is a type of hydrocarbon that contains only single bonds between the central carbon atoms. Alkanes are true hydrocarbons, meaning they contain only hydrogen and carbon atoms. Alkanes are also referred to as saturated hydrocarbons since they have the maximum number of hydrogen atoms per carbon atom, versus the unsaturated hydrocarbons (alkenes and alkynes) which contain fewer hydrogen atoms per carbon atom.
Take for example the three simplest alkanes:
While these examples are very simple alkanes, larger molecules can be branched or cyclic (containing a ring of carbon atoms). The names of all alkanes end with the suffix -ane (e.g. methane). The chemical name of an alkane will include information about the number of carbons in the molecule (such as in the example molecules above) and their arrangement (whether there are branches on the central carbon chain, for example). 
When two molecules have same molecular formula, but have the atoms arranged in a different way, they are called structural isomers. For example, both butane and 2-methylpropane shown below have the same molecular formula C4H9, but have the carbon atoms arranged differently.
The major components of fossil fuels are hydrocarbons, including alkanes such as methane (CH4) - the major component of natural gas, propane (C3H8) - commonly used as BBQ fuel, butane (C4H10) -often used as lighter fuel and octane (C8H18) - an important component of gasoline.
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