Molecule: GCSE Chemistry Definition

Alexandra Brennan

Written by: Alexandra Brennan

Reviewed by: Stewart Hird

Published

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1 minutes

What is a molecule?

In GCSE chemistry, a molecule is a group of two or more atoms chemically combined. Both elements and compounds can exist as molecules. For example, carbon dioxide is a compound and exists as molecules consisting of one carbon atom and two oxygen atoms, CO2. Hydrogen is an element and exists as molecules consisting of two hydrogen atoms, H2

Diagram showing molecular structures: Chlorine (green, two atoms), Nitrogen (blue, two atoms), Ozone (red, three atoms), with labels and colour coding.
Examples of elements existing as molecules
Diagram comparing water (H2O) and carbon dioxide (CO2) molecules, showing their structures with labelled atoms: water as H-O-H, carbon dioxide as O-C-O.
Examples of compounds existing as molecules

Molecules are usually formed from non-metal atoms. They are therefore held together by covalent bonds which involve the sharing of electrons. Substances that exist as molecules usually have low melting and boiling points. Although they have strong covalent bonds between the atoms, there are weak intermolecular forces between the molecules. These require little energy to overcome. Generally, as the size of the molecule increases, so does the melting / boiling point due to the strength of these forces increasing. 

Diagram showing water molecules. Strong covalent bonds within molecules and weak intermolecular forces between hydrogen and oxygen atoms are labelled.
Covalent bonds exist between the atoms in a molecule, and intermolecular forces between the molecules

Molecule Revision Resources to Ace Your Exams

Most exam boards require you to give the formula of common molecules and explain the properties of simple molecules.  To make sure you ace this topic in your exams, you can also practice our exam questions on bonding. 

Explore Our GCSE Chemistry Revision Resources

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Alexandra Brennan

Author: Alexandra Brennan

Expertise: Chemistry

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.

Stewart Hird

Author: Stewart Hird

Expertise: Chemistry Lead

Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Topic Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.

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