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How do constitutional isomers differ from stereoisomers?

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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.)

In chemistry, isomers are compounds that share the same molecular formula—meaning they contain the same number and type of atoms—but possess different chemical and physical properties. They are broadly categorized into two types based on how their components are organized.12

Constitutional Isomers

Constitutional isomers (sometimes called structural isomers) differ in their connectivity. While they consist of the same parts, those atoms are bonded or attached to each other in different sequences. For example, butane and isobutane both have the formula $C_{4} H_{10}$ , but butane features a continuous chain of carbon atoms, whereas isobutane has a branched structure.32

Stereoisomers

In contrast, stereoisomers possess the same connectivity, meaning their atoms are linked in the same order. Instead, they differ in the orientation of their atoms in space. Stereoisomers are further divided into:21

Enantiomers: Molecules that are non-superimposable mirror images of one another, similar to a pair of human hands.12
Diastereomers: All other stereoisomers that are not mirror images of each other.1