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How do butane and isobutane differ in the arrangement of their carbon atoms?

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Two diagrams show the three-dimensional structure of a methane molecule: panel A uses a ball-and-stick model with a central carbon atom connected to four hydrogen atoms in a tetrahedral arrangement, while panel B illustrates the bond angle of 109.5 degrees and bond length of 1.09 angstroms between carbon and hydrogen atoms. — isomerism Tetrahedral geometry of methane: (A) stick-and-ball model and (B) diagram showing bond angles and distances. (Plain bonds represent bonds in the plane of the image; wedge and dashed bonds represent those directed toward and away from the viewer, respectively.)

Butane and isobutane are constitutional isomers with the same molecular formula, $C_{4} H_{10}$ , but they differ in the connectivity of their carbon atoms.12

Butane (often referred to as n-butane) consists of four carbon atoms bonded together in a single, continuous, straight chain.12
Isobutane features a branched structure, meaning its carbon atoms are not arranged in a simple straight line.12

Because of these differences in their carbon skeletons, they are distinct chemical compounds with unique physical and chemical properties, such as different boiling points.12