In organic chemistry, an alkane, or paraffin (a historical name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in which all the carbon-carbon bonds are single. Alkanes have the general chemical formula CnH2n+2. For example, the case of n = 1 is CH4, which is methane. Besides this standard definition by the International Union of Pure and Applied Chemistry, in some authors' usage the term alkane is applied to any saturated hydrocarbon, including those that are either monocyclic (i.e., the cycloalkanes) or polycyclic. In an alkane, each carbon atom has 4 bonds (either C-C or C-H), and each hydrogen atom is joined to one of the carbon atoms (so in a C-H bond). A longest series of linked carbon atoms in the molecule is known as its carbon skeleton or carbon backbone. The number of carbon atoms may be thought of as the size of the alkane, so one might speak for instance of a "C2 alkane." The alkanes range in complexity from the simplest case of methane, CH4 (sometimes called the parent molecule), to arbitrarily large molecules. One group of the higher alkanes are waxes for which the number of carbons in the carbon backbone is greater than about 17. Beyond that the compounds are solids at standard ambient temperature and pressure (SATP). With their repeated -CH2- units, the alkanes constitute a homologous series of organic compounds in which the members differ in molecular mass by multiples of 14.03 u (the total mass of each such methylene-bridge unit, which comprises a single carbon atom of mass 12.01 u and two hydrogen atoms of mass ~1.01 u each). Alkanes are not very reactive and have little biological activity. They can be viewed as molecular trees upon which can be hung the more active/reactive functional groups of biological molecules. The alkanes have two main commercial sources: petroleum (crude oil) and natural gas. An alkyl group, generally abbreviated with the symbol R, is a functional group that, like an alkane, consists solely of single-bonded carbon and hydrogen atoms connected acyclically—for example a methyl or ethyl group.

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