What does Unit 1 of WJEC A-Level Chemistry cover?

Unit 1, The Language of Chemistry, Structure and Physical Chemistry, is the first AS unit. It covers writing formulae and balanced equations, atomic structure and mass spectrometry, the mole and chemical calculations including titrations, ionic, covalent and metallic bonding with molecular shapes, the four solid structures, periodic trends, and an introduction to dynamic equilibrium and the Bronsted-Lowry acid-base theory.

How is Unit 1 examined in WJEC A-Level Chemistry?

Unit 1 is an AS written paper of structured questions and extended responses. Expect mole and titration calculations, balancing equations, mass-spectrum and ionisation-energy interpretation, VSEPR shapes, comparison of solid structures, and explanations of periodic trends. A calculator and a periodic table are provided.

What is the most important skill to master in Unit 1?

Mole calculations. Almost every numerical question uses the relationships moles equals mass over molar mass and moles equals concentration times volume, so practise converting between mass, moles and concentration, scaling with equations, finding empirical formulae and completing titration arithmetic until it is automatic.

How do I predict the shape of a molecule?

Use valence shell electron pair repulsion (VSEPR). Count the bonding and lone pairs around the central atom; they repel to be as far apart as possible. Lone pairs repel more than bonding pairs, so each lone pair reduces the bond angle by about 2.5 degrees.

How should I revise periodic trends?

Learn the trends in atomic radius, ionisation energy, electronegativity and melting point across a period and down a group, and always explain them with nuclear charge, shielding and outer-electron distance. Be ready to account for the two dips in first ionisation energy across a period.

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WJEC A-Level Chemistry Unit 1 The Language of Chemistry, Structure and Physical Chemistry: a deep dive on formulae, atoms, the mole, bonding and simpler equilibria

A deep-dive WJEC A-Level Chemistry guide to Unit 1. Covers formulae and equations, atomic structure and mass spectrometry, the mole and chemical calculations, ionic, covalent and metallic bonding, the four solid structures, periodic trends, and an introduction to equilibria and acid-base reactions.

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What Unit 1 actually demands
Formulae, atoms and calculations
Bonding, structure and the periodic table
Simpler equilibria and acid-base
Check your knowledge

What Unit 1 actually demands

Unit 1 builds the language and number sense of chemistry. Examiners want fluent formula and equation writing, confident mole calculations, accurate bonding and shape work, and clear, cause-and-effect explanations of periodic trends. Definitions are marked strictly, so learn them precisely.

This guide ties together the seven topics of the unit. Each has a matching dot-point page with practice questions; this overview connects them.

Formulae, atoms and calculations

You must write formulae from ion charges, balance full and ionic equations with state symbols, and assign oxidation numbers. Atomic structure covers sub-atomic particles, isotopes, mass spectrometry, electron configurations and ionisation energies. The mole then links mass, the Avogadro constant, concentration and gas volume through $n = m / M_r$ , $n = c \times V$ and $pV = nRT$ .

Bonding, structure and the periodic table

Ionic, covalent and metallic bonding, electronegativity and intermolecular forces explain molecular shapes (by VSEPR) and the four solid structures. Periodic trends in radius, ionisation energy, electronegativity and melting point all follow from nuclear charge, shielding and outer-electron distance.

Simpler equilibria and acid-base

A reversible reaction reaches dynamic equilibrium, whose position shifts in line with Le Chatelier's principle, as in the Haber process. A Bronsted-Lowry acid donates a proton and a base accepts one.

Check your knowledge

Attempt these under timed conditions, then check against the solutions.

Define relative atomic mass. (2 marks)
A sample of chlorine is 75 percent $^{35}$ Cl and 25 percent $^{37}$ Cl. Calculate its relative atomic mass. (2 marks)
Calculate the moles in $25.0$ cm $^3$ of $0.250$ mol dm $^{-3}$ sodium hydroxide. (2 marks)
Predict and explain the shape and bond angle of ammonia. (3 marks)
Explain why aluminium has a lower first ionisation energy than magnesium. (2 marks)
State Le Chatelier's principle. (2 marks)

Sources & how we know this

WJEC A-level Chemistry specification — WJEC (2015)