A structural isomer is a type of isomer that has the same molecular formula as another compound but differs in the arrangement of atoms. This variation in structure can lead to different physical and chemical properties. For example, the compounds butane and isobutane both have the formula C₄H₁₀, but their structures are arranged differently. Structural isomers can be classified into different categories, such as chain isomers and positional isomers. Chain isomers differ in the branching of the carbon chain, while positional isomers have the same carbon skeleton but differ in the location of functional groups. Understanding structural isomers is essential in fields like organic chemistry and pharmaceuticals.