Paraffin wax

Sodium in paraffin oil

In chemistry, paraffin is the common name for the alkane hydrocarbons with the general formula C_nH_2n+2. Paraffin wax refers to the solids with n between 20 and 40, inclusive.

The simplest paraffin molecule is that of methane, CH₄, a gas at room temperature. Heavier members of the series, such as that of octane, C₈H₁₈, and mineral oil appear as liquids at room temperature. The solid forms of paraffin, called paraffin wax, are from the heaviest molecules from C₂₀H₄₂ to C₄₀H₈₂. Paraffin wax was identified by Carl Reichenbach in 1830.

Paraffin, or paraffin hydrocarbon, is also the technical name for an alkane in general, but in most cases it refers specifically to a linear, or normal alkane — whereas branched, or isoalkanes are also called isoparaffins. It is distinct from the fuel known in Ireland, Britain and South Africa as paraffin oil or just paraffin, which is called kerosene in most of the U.S., Australia and New Zealand.

The name is derived from the Latin parum (= barely) + affinis with the meaning here of "lacking affinity", or "lacking reactivity". This is because alkanes, being non-polar and lacking in functional groups, are very unreactive.