The chemical compounds known as alkanes (or paraffins) are the simplest organic compounds and the least reactive hydrocarbons. They are made exclusively of hydrogen and carbon atoms arranged in straight or branched chains with single carbon-carbon bonds. Only the straight (or normal) alkanes are shown. The general formula for an alkane is . In industry, alkanes are used directly as fuels or as feedstocks for plastics and other products. The number of isomers for each alkane is shown (an isomer has the same molecular formula, but a different structural formula).