Advanced Placement (AP) Biology Practice Exam

Structural isomers differ in what aspect?

1. Their molecular weight

2. Their covalent arrangement of atoms

3. Their state of matter

4. Their solubility in water

The correct answer is: Their covalent arrangement of atoms

Structural isomers are compounds that share the same molecular formula but differ in the way their atoms are connected or arranged. This variation in the covalent arrangement of atoms results in different structural frameworks, which can lead to distinct chemical properties and reactivities among the isomers. For instance, two structural isomers could have the same number of carbon and hydrogen atoms, but their different connectivity might alter boiling points, functional group positioning, and overall behavior in chemical reactions. While molecular weight remains constant for isomers with the same formula, the state of matter and solubility in water can vary among different substances, but these properties do not define structural isomerism. Thus, understanding structural isomers revolves around their unique arrangements rather than the other choices listed.