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Isomer - IGCSE Chemistry Definition

Reviewed by: Alexandra Brennan

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An isomer refers to a molecule that shares the same molecular formula as another molecule but differs in structural arrangement, resulting in distinct chemical properties. In IGCSE Chemistry, students learn that isomers can vary in terms of the order of atom connections (structural isomers) or the spatial orientation of atoms (stereoisomers), despite having identical numbers and types of atoms.

Structural formulas of propene and cyclopropane, both with the molecular formula C3H6, shown side by side for comparison.
Isomers of C3H6 show the same molecular formula but different structures

Understanding isomers is important because they highlight how different chemical structures can influence the behaviour and characteristics of compounds, even when they are composed of the same elements in the same proportions.

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Alexandra Brennan

Reviewer: Alexandra Brennan

Expertise: Chemistry Content Creator

Alex studied Biochemistry at Newcastle University before embarking upon a career in teaching. With nearly 10 years of teaching experience, Alex has had several roles including Chemistry/Science Teacher, Head of Science and Examiner for AQA and Edexcel. Alex’s passion for creating engaging content that enables students to succeed in exams drove her to pursue a career outside of the classroom at SME.

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