Hydrocarbons are the most reduced compounds of all, with nothing but C and H atoms. Hydrocarbons with single C-C bonds, known as saturated hydrocarbons or alkanes, can be thought of as being built by the snapping together of carbon tetrahedra, with unused carbon bonding positions filled by hydrogen atoms.

There are as many different saturated hydrocarbons as there are ways of connecting tetrahedra. The simplest are the straight-chain alkanes (designated "n-" for "normal"), which are shown on the opposite page.

Methane, ethane, propane, and butane are traditional names for these compounds, but from pentane and hexane onward, the name is derived from the Greek or Latin word for the number of carbons, plus the suffix "-ane" to indicate a saturated hydrocarbon.

The straight-chain n-octane molecule at the bottom of the opposite page is not the only way of constructing a C8H18 molecule.