GCSE AQA Chemistry: Complete Topic Guide & Revision Tips

1. Atomic Structure and the Periodic Table

Learn about atoms, elements, compounds, and how the periodic table is organised.

• Atoms are the smallest particles of an element, made of protons, neutrons, and electrons.
• Atomic number = number of protons; mass number = protons + neutrons.
• Isotopes are atoms of the same element with different numbers of neutrons.
• Elements are arranged in order of atomic number in the periodic table.
• Groups contain elements with similar chemical properties.
• Periods show repeating trends in properties.
• Metals are on the left; non-metals on the right of the periodic table.
• Noble gases (Group 0) are unreactive due to full outer shells.
• Alkali metals (Group 1) are very reactive and increase in reactivity down the group.
• Halogens (Group 7) decrease in reactivity down the group.

2. Bonding, Structure and the Properties of Matter

Explore how atoms bond and how this affects the properties of substances.

• Ionic bonding: transfer of electrons between metals and non-metals.
• Covalent bonding: sharing of electrons between non-metals.
• Metallic bonding: delocalised electrons in a lattice of positive ions.
• Ionic compounds have high melting/boiling points and conduct electricity when molten or dissolved.
• Simple molecular substances have low melting/boiling points and do not conduct electricity.
• Giant covalent structures (e.g., diamond, graphite) have high melting points.
• Metals are malleable, ductile, and good conductors of heat and electricity.
• Alloys are mixtures of metals with improved properties.
• Polymers are long chains of repeating units; properties depend on monomers and bonding.
• Nanoparticles have unique properties due to their small size and large surface area.

3. Quantitative Chemistry

Master calculations involving masses, moles, and chemical equations.

• Relative atomic mass (Ar) and relative formula mass (Mr) are used in calculations.
• The mole is a unit for amount of substance (Avogadro’s number = 6.02 × 10²³).
• Calculate moles: moles = mass ÷ Mr.
• Balanced equations show the ratio of moles of reactants and products.
• Conservation of mass: total mass of reactants = total mass of products.
• Calculate concentrations: concentration = mass ÷ volume.
• Percentage yield = (actual yield ÷ theoretical yield) × 100%.
• Atom economy = (Mr of desired product ÷ total Mr of reactants) × 100%.
• Limiting reactant determines the amount of product formed.
• Titrations are used to find concentrations of acids and alkalis.

4. Chemical Changes

Study reactions of acids, bases, metals, and electrolysis.

• Acids release H⁺ ions in water; alkalis release OH⁻ ions.
• pH scale measures acidity/alkalinity (0 = most acidic, 14 = most alkaline).
• Neutralisation: acid + base → salt + water.
• Reactivity series ranks metals by how easily they lose electrons.
• Displacement reactions: a more reactive metal displaces a less reactive one.
• Extraction of metals: reduction with carbon or electrolysis.
• Electrolysis splits ionic compounds using electricity.
• At the cathode, positive ions gain electrons (reduction).
• At the anode, negative ions lose electrons (oxidation).
• Redox reactions involve both reduction and oxidation.

5. Energy Changes

Examine exothermic and endothermic reactions and their applications.

• Exothermic reactions release energy (temperature rises).
• Endothermic reactions absorb energy (temperature falls).
• Examples: combustion (exothermic), thermal decomposition (endothermic).
• Energy profile diagrams show energy changes during reactions.
• Activation energy is the minimum energy needed to start a reaction.
• Bond breaking is endothermic; bond making is exothermic.
• Calculate energy changes using bond energies.
• Everyday uses: self-heating cans, cold packs.
• Cells and batteries convert chemical energy to electrical energy.
• Fuel cells produce electricity from hydrogen and oxygen.

6. The Rate and Extent of Chemical Change

Learn about factors affecting reaction rates and reversible reactions.

• Rate of reaction = change in amount ÷ time.
• Factors: temperature, concentration, surface area, catalysts.
• Increasing temperature increases rate (more collisions, more energy).
• Higher concentration/pressure increases rate (more particles).
• Smaller particle size (greater surface area) increases rate.
• Catalysts speed up reactions without being used up.
• Reversible reactions can go both ways; shown by ⇌ symbol.
• Dynamic equilibrium: forward and backward reactions occur at the same rate.
• Le Chatelier’s Principle: changing conditions shifts equilibrium.
• Industrial processes (e.g., Haber process) use these principles for efficiency.

7. Organic Chemistry

Study carbon compounds, including hydrocarbons, alcohols, and polymers.

• Organic chemistry is the study of carbon compounds.
• Alkanes are saturated hydrocarbons (single bonds, CnH2n+2).
• Alkenes are unsaturated hydrocarbons (double bonds, CnH2n).
• Crude oil is separated by fractional distillation.
• Cracking breaks long hydrocarbons into shorter, more useful ones.
• Alcohols, carboxylic acids, and esters are important functional groups.
• Polymers are made from monomers by addition or condensation polymerisation.
• Combustion of hydrocarbons produces CO₂ and H₂O.
• Biofuels and biodegradable polymers are alternatives to traditional fuels/plastics.
• Structure and properties of molecules affect their uses.

8. Chemical Analysis

Discover methods for identifying substances and testing purity.

• Pure substances have fixed melting/boiling points.
• Formulations are mixtures with a precise purpose (e.g., medicines, paints).
• Chromatography separates mixtures and identifies components.
• Flame tests identify metal ions by colour.
• Tests for gases: hydrogen (pop with lit splint), oxygen (relights glowing splint), carbon dioxide (limewater turns cloudy), chlorine (bleaches damp litmus).
• Precipitation reactions identify metal ions.
• Instrumental methods (e.g., mass spectrometry) are sensitive and accurate.
• Rf value = distance travelled by substance ÷ distance travelled by solvent.
• Qualitative analysis identifies what is present; quantitative analysis measures how much.
• Water purity is tested by boiling point and chemical analysis.

9. Chemistry of the Atmosphere

Explore the composition, evolution, and pollution of Earth’s atmosphere.

• Earth’s early atmosphere was mostly CO₂, with little oxygen.
• Photosynthesis increased oxygen and reduced CO₂.
• Current atmosphere: ~78% nitrogen, ~21% oxygen, small amounts of other gases.
• Greenhouse gases (CO₂, methane, water vapour) trap heat and cause global warming.
• Human activities increase greenhouse gas levels.
• Climate change leads to rising sea levels, extreme weather, and habitat loss.
• Pollutants: carbon monoxide, sulfur dioxide, nitrogen oxides, particulates.
• Acid rain is caused by sulfur dioxide and nitrogen oxides.
• Reducing emissions helps protect the environment.
• Carbon footprint measures total greenhouse gas emissions.

10. Using Resources

Learn about sustainable use of Earth’s resources and recycling.

• Finite resources will eventually run out; renewable resources can be replaced.
• Potable water is safe to drink but not pure.
• Water is treated by filtration and sterilisation.
• Waste water is treated before release into the environment.
• Life cycle assessments compare environmental impact of products.
• Recycling reduces use of raw materials and energy.
• Corrosion prevention extends the life of materials.
• Alloys, ceramics, polymers, and composites have different properties and uses.
• Phytomining and bioleaching extract metals from low-grade ores.
• Sustainable development balances needs of society, economy, and environment.

Further Support

For detailed notes, practice questions, and interactive resources on every GCSE AQA Chemistry topic, visit TRH Learning.