Chain isomerism is a type of structural isomerism where two or more compounds have the same molecular formula, but the way their carbon atoms are joined together differs from isomer to isomer/Fundamentals/Isomerism_in_Organic_Compounds/Structural_Isomerism_in_Organic_Molecules). In other words, chain isomers have a different skeletal arrangement for the compound, whereas position isomers have the same functional group or substituent that is in a different position. For example, pentane, C5H12, has three chain isomers: pentane, 2-methylbutane, and 2,2-dimethylpropane/Fundamentals/Isomerism_in_Organic_Compounds/Structural_Isomerism_in_Organic_Molecules). The unbranched "straight chain" isomer of C5H12 is pentane, while the other two isomers are branched. 2-methylbutane has one branch, and 2,2-dimethylpropane has two branches, each containing one carbon atom and is a methyl group, —CH3.