CnH2n−4, CnH2n−6. In modern nomenclature, the first three specifically name hydrocarbons with single, double and triple bonds; while "-one" now represents a ketone. Linear alkanes Straight-chain alkanes are sometimes indicated by the prefix "n-" or "n-"(for "normal") where a non-linear isomer exists. Although this is not strictly necessary and is not part of the IUPAC naming system, the usage is still common in cases where one wishes to emphasize or distinguish between the straight-chain and branched-chain isomers, e.g., "n-butane" rather than simply "butane" to differentiate it from isobutane. Alternative names for this group used in the petroleum industry are linear paraffins or n-paraffins. The first six members of the series (in terms of number of carbon atoms) are named as follows: methane CH4 – one carbon and 4 hydrogen ethane C2H6 – two carbon and 6 hydrogen propane C3H8 – three carbon and 8 hydrogen butane C4H10 – four carbon and 10 hydrogen pentane C5H12 – five carbon and 12 hydrogen hexane C6H14 – six carbon and 14 hydrogen The first four names were derived from methanol, ether, propionic acid and butyric acid. Alkanes with five or more carbon atoms are named by adding the suffix -ane to the appropriate numerical multiplier prefix with elision of any terminal vowel (-a or -o) from the basic numerical term. Hence, pentane, C5H12; hexane, C6H14; heptane, C7H16; octane, C8H18; etc. The numeral prefix is generally Greek; however, alkanes with a carbon atom count ending in nine, for example nonane, use the Latin prefix non-. For a more complete list, see list of straight-chain alkanes. Branched alkanes Simple branched alkanes often have a common name using a prefix to distinguish them from linear alkanes, for example n-pentane, isopentane, and neopentane. IUPAC naming conventions can be used to produce a systematic name. The key steps in the naming of more complicated branched alkanes are as follows: Identify the longest continuous chain of carbon atoms Name this longest root chain using standard naming rules Name each side chain by changing the suffix of the name of the alkane from "-ane" to "-yl" Number the longest continuous chain in order to give the lowest possible numbers for the side-chains Number and name the side chains before the name of the root chain If there are multiple side chains of the same type, use prefixes such as "di-" and "tri-" to indicate it as such, and number each