Alkanes are substances that belong to a homologous series of organic compounds that contain the elements carbon and hydrogen only, and whose members differ by constant relative molecular mass of 14. In an alkane, each carbon atom and hydrogen atom are held together by saturated covalent bonds; the general molecular formula for alkanes is CnH2n+2. In contemporary industrial societies, these hydrocarbons are most often as fuels and to produce chemicals, such as methane and octane. These chemicals are derived from the fractional distillation of crude oil and via catalytic cracking. Alkanes are insoluble in water, and have a lower density thus making them float atop water.
When alkanes have more than three carbon atoms, they can be arranged in different ways, in a line or branched fashion. The different arrangements are called isomers, with standardized nomenclature to describe the isomeric forms. See IUPAC nomenclature.
Linear chained alkanes with fewer than 4 carbon atoms have special names:
- 1 carbon atom : Methane, CH4
- 2 carbon atoms: Ethane, C2H6
- 3 carbon atoms: Propane, C3H8
- 4 carbon atoms: Butane, C4H10
When alkanes have more than 4 carbon atoms, they are named using a Greek numeral prefix plus -ane suffix, e.g. pentane (C5H12), hexane (C6H14). All alkanes contain single-bonded carbon atoms.