Propane and butane

LPG is a mixture of two flammable but nontoxic gases called propane and butane. Both of these are hydrocarbons (their molecules are made from different combinations of hydrogen and carbon atoms): propane molecules (C3H8) have eight hydrogen atoms attached to three carbon atoms, while butane molecules (C4H10) have ten hydrogen atoms bonded to four carbon atoms. LPG sometimes contains a variation of butane called isobutane, which has the same component atoms (four carbons and ten hydrogens) connected together in a slightly different way.