The first part of an organic name shows how many carbon atoms are in the chain: meth- is one, eth- is two, prop- is three, but- is four and pent- is five. The ending shows the series. The first four straight chain alkanes are methane, ethane, propane and butane. The first four alkenes are ethene, propene, butene and pentene, because an alkene needs at least two carbon atoms to have a double bond. The first four alcohols are methanol, ethanol, propanol and butanol. The first four carboxylic acids are methanoic acid, ethanoic acid, propanoic acid and butanoic acid.
Formulae: methane CH4, ethane C2H6, propane C3H8, butane C4H10. Ethene C2H4, propene C3H6, butene C4H8. Ethanol C2H5OH. Ethanoic acid CH3COOH.
A fully displayed formula shows every atom and every bond. Each carbon atom forms four bonds, each hydrogen atom forms one bond and each oxygen atom forms two bonds. In methane the carbon atom forms four single bonds to four hydrogen atoms. In ethene the two carbon atoms are joined by a double bond. In an alcohol the oxygen atom is bonded to a carbon atom and to a hydrogen atom. In a carboxylic acid the -COOH group has a C=O double bond and an O-H bond on the same carbon atom.
