SQA National 5 Chemistry Practice Exam

Isomers are defined as molecules that have the same molecular formula but differ in their structural arrangement. This means that while the number and type of atoms are the same in isomeric compounds, the way those atoms are bonded or arranged in space differs, leading to variations in their structural formulas.

This structural difference can result in distinct chemical and physical properties, allowing for a multitude of isomers to exist for a given molecular formula. For example, butane (C4H10) can be found in two structural forms: n-butane and isobutane, which have different physical properties and reactivity.

The other definitions do not accurately represent isomers. Molecules with different molecular formulas represent distinct compounds rather than isomers. Compounds that differ in chemical properties may be the result of isomerism, but this definition is too broad and doesn’t specifically address the concept of isomers. Lastly, molecules with identical structural formulas cannot be considered isomers because they are the same compound, not different forms. Thus, the correct understanding of isomers lies in their shared molecular formula combined with varying structural arrangements.