What does the Substances and atomic structure module cover?

This module gathers WJEC Unit 1 topics 1.1 (the nature of substances and chemical reactions) and 1.2 (atomic structure and the Periodic Table). It covers classifying elements, compounds and mixtures, reading chemical formulae, word and balanced symbol equations, conservation of mass, paper chromatography and Rf values, the structure of the atom, isotopes and relative atomic mass, electronic structure, and the trends in Groups 1, 7 and 0 of the Periodic Table.

Which unit and paper assess this module?

These topics are part of Unit 1 (Chemical substances, reactions and essential resources), assessed on the Unit 1 written paper. The paper is 1 hour 45 minutes, worth 80 marks and 45 percent of the qualification, sat at Foundation or Higher tier.

What maths skills are needed here?

You need to balance symbol equations, apply conservation of mass to work out masses of reactants or products, calculate Rf values in chromatography, work out numbers of protons, neutrons and electrons, and calculate relative atomic mass as a weighted mean from isotopic abundances.

What kinds of question come up?

Expect questions classifying substances, reading and balancing formulae and equations, explaining conservation of mass, describing the chromatography method and calculating Rf, counting sub-atomic particles, defining and using isotopes, writing electronic structures, and explaining the reactivity trends in Groups 1 and 7 and the inertness of Group 0.

How should I revise this module?

Learn the definitions of element, compound and mixture and the signs of a chemical reaction. Drill balancing equations until it is automatic, and practise conservation-of-mass calculations. Memorise the relative masses and charges of the sub-atomic particles, the shell-filling rules and the electronic structures of the first twenty elements, and the Group 1, 7 and 0 trends with their electron explanations. Use WJEC past papers and watch the command words.

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WJEC GCSE Chemistry: Substances and atomic structure (Unit 1.1 to 1.2) overview

An overview of the Substances and atomic structure module in WJEC GCSE Chemistry, mapping topics 1.1 and 1.2: elements, compounds and mixtures, equations and conservation of mass, chromatography, atomic structure and isotopes, electronic structure, and the Periodic Table and its groups.

Generated by Claude Opus 4.87 min readWJEC Chemistry 1.1 to 1.2Updated 2026-06-14

Reviewed by: AI editorial process; not yet individually human-reviewed

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The topics in this module
How this module fits the exam
How to study this module

The Substances and atomic structure module gathers WJEC Unit 1 topics 1.1 (the nature of substances and chemical reactions) and 1.2 (atomic structure and the Periodic Table). It introduces the language of chemistry, how reactions are represented, and the structure of the atom that explains the whole Periodic Table. Everything later in the course (bonding, reactions, calculations) builds on these ideas. This page maps the module and links to a focused answer page for each part.

The topics in this module

Elements, compounds and mixtures: Classifying substances, reading chemical formulae, and telling physical changes from chemical reactions using evidence such as colour change and gas production. See Elements, compounds and mixtures.
Chemical reactions and equations: Word and balanced symbol equations, state symbols, the law of conservation of mass, and identifying exothermic and endothermic reactions. See Chemical reactions and equations.
Chromatography: The paper chromatography method, why components separate, interpreting a chromatogram and calculating Rf values. See Chromatography.
Atomic structure and isotopes: Sub-atomic particles and their relative masses and charges, atomic and mass number, particles in atoms and ions, isotopes, and relative atomic mass. See Atomic structure and isotopes.
Electronic structure: How electrons fill shells, the electronic structures of the first twenty elements, and linking outer electrons to group and shells to period. See Electronic structure.
The Periodic Table and groups: The arrangement of the table, metals and non-metals, and the trends in Group 1, Group 7 and Group 0. See The Periodic table and groups.

How this module fits the exam

These topics sit in Unit 1, assessed on the Unit 1 written paper (1 hour 45 minutes, 80 marks, 45%). Questions mix recall (definitions, trends), skills (balancing, chromatography method) and calculation (conservation of mass, Rf, relative atomic mass).

How to study this module

Nail the vocabulary. Element, compound, mixture, reactant, product, exothermic, endothermic, isotope - precise definitions earn marks.
Drill balancing. Practise putting numbers in front of formulae until balancing equations is automatic.
Learn the particle facts. Relative masses and charges of protons, neutrons and electrons, and how to find each from atomic and mass number.
Memorise shell filling. 2, 8, 8 for the first twenty elements, and how the structure gives group and period.
Learn the group trends. Group 1 more reactive down, Group 7 less reactive down, Group 0 inert - each with the electron explanation.

Then test yourself with the module quiz.

Sources & how we know this

WJEC GCSE Chemistry specification (from 2016) — WJEC (2016)