AQA A-Level Chemistry

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3.1 - Physical chemistry

3.1.1 - Atomic structure

3.1.1.1 - Fundamental ParticlesChemists did not discover the structure of the atom in one step. The model changed as new evidence appeared, and each new model explained observations better than the one before it. Learn how evidence changed atomic models, how particle charge differs from mass, and how the nucleus and electrons...
3.1.1.2 - Mass Number and IsotopesThis lesson links simple atomic structure to one of chemistry's most useful analytical tools. Particle counts, isotope notation, and mass spectra are different ways of describing the same atoms, so the ideas make most sense when you connect them. By the end, you should be able to explain isotopes...
3.1.1.3 - Electron ConfigurationElectron configurations let us describe exactly where electrons are in an atom, while ionisation energy data lets us test whether that description makes sense. In this lesson, you will build electron configurations for atoms and ions up to krypton and then use first and successive ionisation ener...

3.1.2 - Amount of substance

3.1.2.1 - Relative Atomic and Molecular MassChemists do not usually work with the actual masses of individual atoms and molecules because those masses are far too small to handle conveniently. Instead, they compare particles against a fixed standard and use relative values. In this lesson, you will learn exactly what Ar and Mr mean...
3.1.2.2 - The Mole and the Avogadro ConstantChemists cannot count atoms, ions, or molecules one by one, so they use the mole as a counting unit. This lesson shows how the mole links mass, number of particles, concentration in solution, and the ratios in chemical equations. By the end, you should be able to move confidently between these id...
3.1.2.3 - The Ideal Gas EquationThe ideal gas equation links together four measurable properties of a gas: pressure, volume, temperature, and amount of substance. It turns a gas sample into something you can calculate with, provided each value is written in the correct unit. This lesson focuses on using pV = nRT accurately,...
3.1.2.4 - Empirical and Molecular FormulaWhen chemists know how much of each element is present in a substance, they can work backwards to its formula. That turns a list of masses or percentages into a genuine clue about what the substance is. In this lesson, you will learn how to turn composition data into an empirical formula, then ho...
3.1.2.5 - Balanced Equations and Associated CalculationsEvery chemical calculation in this topic starts with one idea: a balanced equation tells you the exact mole ratio in which particles react. If the equation is wrong, every mass, gas volume, concentration, yield, and atom economy answer built from it will also be wrong. In this lesson, you will le...
Required practical 1 - Standard Solutions and Acid-Base TitrationThis required practical is about making concentration data trustworthy. First you prepare a solution with an accurately known concentration, then you use that solution in a titration to find the concentration of another acid or alkali. To do that confidently, you need more than a recipe: you need...

3.1.3 - Bonding

3.1.3.1 - Ionic BondingIonic bonding explains how metals and non-metals form compounds by making ions, and how those ions are held together in a giant structure. In this lesson, you will build the particle model first, then use it to predict ion charges and construct correct formulae for ionic compounds, including ones...
3.1.3.2 - Covalent and Dative BondingCovalent bonding is really about electron pairs: who is sharing them, how many pairs are shared, and how we represent that clearly on paper. Once that idea is secure, every line and every arrow starts to carry real meaning rather than just looking like notation. In this lesson, we will build that...
3.1.3.3 - Metallic BondingMetallic bonding explains why a piece of metal behaves as one joined-up structure rather than a pile of separate atoms. In this lesson, the focus stays tightly on the model itself: positive ions arranged in a lattice, delocalised electrons, and the attraction between them. By the end, you should...
3.1.3.4 - Bonding and Physical PropertiesBonding determines how particles are arranged in a solid, and that arrangement controls what happens when you heat the substance or try to make it conduct electricity. In this lesson, you will compare the four crystal structures in the specification using sodium chloride, magnesium, iodine, ice,...
3.1.3.5 - Shapes of Molecules and IonsThe shape of a simple molecule or ion is not chosen at random. It comes from how pairs of electrons around a central atom repel each other and spread out in three dimensions. In this lesson, you will learn how to count those electron pairs, predict the arrangement they make, and explain why lone...
3.1.3.6 - Bond PolarityBond polarity explains why some covalent bonds have slightly positive and slightly negative ends instead of being perfectly even. The key idea is simple: if two bonded atoms attract the shared pair of electrons by different amounts, the electron distribution becomes uneven. In this lesson, you wi...
3.1.3.7 - Forces Between MoleculesWhen simple molecular substances melt or boil, the covalent bonds inside each molecule are not broken. Molecules move farther apart as the attractions between neighboring molecules are overcome. In this lesson, you will learn how to identify the three intermolecular forces in the specification, e...

3.1.4 - Energetics

3.1.4.1 - Enthalpy ChangeChemical reactions do not just rearrange atoms; they also transfer energy between the reacting system and its surroundings. In this lesson, you will pin down what ΔH means, how to tell whether a reaction is exothermic or endothermic, and how to define the standard enthalpy of combustion...
3.1.4.2 - CalorimetryCalorimetry lets you estimate an enthalpy change from something you can measure directly: a temperature change in a substance of known mass. The heart of the topic is learning what q = mcΔT is really telling you, then linking that energy change to the amount of reaction that took place....
Required practical 2 - Calorimetry and Enthalpy ChangesCalorimetry is how chemists estimate an enthalpy change from a temperature change. In this required practical, you need to turn measurements of mass, volume, and temperature into a value for ΔH in kJ mol⁻¹, then judge how trustworthy that value is. The same co...
3.1.4.3 - Applications of Hess's LawSome enthalpy changes are straightforward to measure directly, but many useful reactions are not. Hess's law lets us calculate the enthalpy change for a difficult reaction by linking it to reactions whose enthalpy changes are known. In this lesson you will learn how to use Hess's law with enthalp...
3.1.4.4 - Bond EnthalpiesWhen a reaction happens, some bonds must be broken and new bonds must form. Bond enthalpies let us estimate the overall enthalpy change by comparing the energy taken in for bond breaking with the energy released by bond formation. In this lesson, you will pin down the exact meaning of mean bond e...

3.1.5 - Kinetics

3.1.5.1 - Collision TheoryCollision theory explains reaction rate by focusing on what happens when particles meet. A reaction does not happen just because particles are present near each other: they must actually collide, and that collision has to be good enough to start chemical change. In this lesson, we will pin down w...
3.1.5.2 - Maxwell-Boltzmann DistributionIn a gas, particles do not all move with the same speed, so they do not all have the same kinetic energy. A Maxwell-Boltzmann distribution shows how those energies are spread across a sample. In this lesson, you will learn how to sketch the curve correctly and how changing temperature changes wha...
3.1.5.3 - Effect of Temperature on Reaction RateTemperature is one of the quickest ways to change how fast a chemical reaction happens. The interesting part is that a small rise in temperature can make a reaction speed up far more than you might expect. That happens because temperature does much more than simply make particles move faster.
Required practical 3 - Temperature and Reaction RateIn this required practical, you do not track concentration continuously with an instrument. Instead, you time how long it takes for a fixed amount of sulfur to form as sodium thiosulfate reacts with hydrochloric acid. By keeping everything except temperature the same, you can use that time to com...
3.1.5.4 - Effect of Concentration and PressureThis lesson is about one simple but powerful idea: reactions go faster when reacting particles collide more often. We will follow that idea in two different settings, changing concentration and changing gas pressure. The key is to connect what changes in the container to what happens to collision...
3.1.5.5 - CatalystsCatalysts matter because they let reactions happen faster without needing harsher conditions. In this lesson, you will pin down what a catalyst actually does, see how it changes the energy pathway of a reaction, and use a Maxwell-Boltzmann distribution to explain why a gas reaction becomes faster...

3.1.9 - Rate equations

3.1.9.1 - Rate EquationsA rate equation tells you more than just whether a reaction is fast or slow. It shows exactly how the rate depends on the concentration of each relevant species, and it gives a route into the temperature dependence of reactions through the Arrhenius equation. In this lesson you will learn how to...
3.1.9.2 - Determination of Rate EquationA rate equation is not taken from the balanced equation. It is worked out from experimental data, because the coefficients in the chemical equation tell you the stoichiometry, not which particles control the speed of the reaction. In this lesson, you will turn concentration-time information into...
Required practical 7 - Initial Rates and Continuous MonitoringThis required practical is about choosing a method that makes rate visible. In one method, you time how long it takes for a fixed event to happen, such as the sudden blue-black colour in the iodine clock. In the other, you collect data continuously as the reaction proceeds, such as gas volume aga...

3.1.11 - Electrode potentials and electrochemical cells

3.1.11.1 - Electrode Potentials and CellsElectrode potentials let us compare how strongly different species attract or release electrons. Once those values are measured under standard conditions, we can arrange them in an electrochemical series, calculate the emf of a cell, and predict whether a simple redox reaction will go forwards. T...
Required practical 8 - Electrochemical Cell EMFThis required practical shows how a redox reaction can be turned into a measurable voltage. You will build a cell from two half-cells, use a salt bridge to complete the circuit, and read the emf with a high-resistance voltmeter. The useful part of the setup is that each component has a clear job,...
3.1.11.2 - Commercial Applications of Electrochemical CellsCommercial cells are electrochemical cells designed to deliver useful electrical energy in everyday devices and larger systems. Different uses need different trade-offs: a watch needs a cell that lasts for a long time, a phone needs a cell that can be recharged many times, and a vehicle may need...

3.1.12 - Acids and bases

3.1.12.1 - Brønsted-Lowry Acid-Base EquilibriaBrønsted-Lowry theory explains acids and bases in a very direct way: by tracking a proton from one species to another. That makes it especially useful in aqueous chemistry, where water often takes part in the proton transfer itself. In this lesson, we will focus on how to identify acids and bases...
3.1.12.2 - Definition and Determination of pHpH gives chemists a compact way to describe hydrogen ion concentration in aqueous solution. That matters because the values involved are often very small, so writing them directly in standard form can make patterns hard to spot. In this lesson, you will learn exactly what pH means, how to convert...
3.1.12.3 - The Ionic Product of Water, KwThis lesson is about the tiny extent to which water dissociates and why that tiny change still matters in acid-base chemistry. Even pure water is quietly producing a few ions all the time. You will see where Kw comes from, why its value changes with temperature, and how to use it to calculate...
3.1.12.4 - Weak Acids, Bases and KaWeak acids and weak bases do not react completely with water, so their solutions contain an equilibrium mixture rather than a single set of products. In this lesson, the main focus is weak acids: how to describe their partial dissociation, how to build the expression for Ka, and how to calcul...
3.1.12.5 - pH Curves, Titrations and IndicatorsAcid-base titrations give you two kinds of information at once. The titre lets you calculate an unknown concentration, and the pH curve shows how the chemistry changes as neutralisation is approached and then passed. In this lesson, you will learn how to read and sketch the four standard pH curve...
Required practical 9 - Acid-Base Titration CurvesThis required practical is about following the whole pH change during a reaction, not just spotting one colour change. By measuring pH after small additions of base, you can compare two titration curves and explain how acid and base strength affect the starting pH, the steepness of the curve, and...
3.1.12.6 - Buffer ActionBuffers matter because many chemical and biological systems only work well over a narrow pH range. In this lesson, you will see what an acidic buffer and a basic buffer are, why they resist sudden pH change, and how to calculate the pH of an acidic buffer. The key idea is that a buffer contains b...

3.2 - Inorganic chemistry

3.2.5 - Transition metals

3.2.5.1 - General Properties of Transition MetalsUse electron configurations to recognise transition metals, then describe their characteristic ions, ligands and co-ordinate bonds.
3.2.5.2 - Substitution ReactionsFollow ligand substitution by counting donor atoms, tracking complex charge and comparing observations; then explain chelation and oxygen transport by haemoglobin.
3.2.5.3 - Shapes of Complex IonsDraw complex-ion geometries with correct co-ordination numbers, bond angles and three-dimensional conventions, and distinguish geometric and optical isomers.
3.2.5.4 - Formation of Coloured IonsExplain colour through absorption of visible light, calculate the energy gap, and use a calibration graph to measure the concentration of a coloured solution.
3.2.5.5 - Variable Oxidation StatesConnect changing oxidation states to vanadium colours, the Tollens test and quantitative redox titrations.
3.2.5.6 - Catalysts (Transition Metals)Explain surface catalysis and catalytic cycles, then use reaction equations and concentration–time graphs to analyse homogeneous catalysis and autocatalysis.

3.3 - Organic chemistry

3.3.1 - Introduction to organic chemistry

3.3.1.1 - NomenclatureOrganic chemistry becomes much easier when you can move fluently between a name, a formula, and a structure. This lesson builds that fluency. You will learn what the main organic formula types show, what makes compounds belong to the same homologous series, and how to name or build simple organic...
3.3.1.2 - Reaction MechanismsReaction mechanisms are the "how" behind an organic reaction. Instead of only showing reactants and products, they show which electrons move, so you can see why one bond forms while another breaks. In this lesson, you will separate free-radical steps from electron-pair mechanisms and learn the dr...
3.3.1.3 - IsomerismIsomerism matters because one molecular formula can describe more than one compound, and those compounds can behave very differently. In this lesson, you will separate structural isomerism from stereoisomerism, learn the three named types of structural isomer, and then use restricted rotation and...

3.3.2 - Alkanes

3.3.2.1 - Fractional Distillation of Crude OilPetroleum, usually called crude oil before refining, is one of the main raw materials of organic chemistry. This lesson focuses on two linked ideas: what alkanes are, and why a refinery can separate a complicated mixture of them into useful fractions. If you can explain why different hydrocarbons...
3.3.2.2 - Modification of Alkanes by CrackingCrude oil does not naturally contain hydrocarbons in the same proportions that industry wants to use them. Refineries therefore need a way to turn less useful long-chain molecules into shorter, more valuable ones. Cracking does exactly that, and this lesson will help you compare thermal and catal...
3.3.2.3 - Combustion of AlkanesAlkanes are widely used as fuels because burning them releases a large amount of energy. That makes them useful, but it also creates a chemistry trade-off: if combustion is not well controlled, several harmful pollutants are formed. In this lesson, you will move from combustion equations to real...
3.3.2.4 - Chlorination of AlkanesWhen methane reacts with chlorine, the visible outcome is simple: one hydrogen atom is replaced by a chlorine atom. The interesting chemistry lies in how that replacement happens. This lesson shows the reaction as a free-radical substitution mechanism and breaks it into the three stages: initiati...

3.3.3 - Halogenoalkanes

3.3.3.1 - Nucleophilic SubstitutionHalogenoalkanes are useful starting molecules because the carbon-halogen bond can be replaced by a different group. This lesson is about spotting why that carbon is vulnerable, following the electron pair in the mechanism, and then adapting the same core pattern for OH-, CN-, an...
3.3.3.2 - Elimination (Halogenoalkanes)When 2-bromopropane reacts with potassium hydroxide, the chemistry is not locked into just one pathway. The same hydroxide ion can either attack a carbon atom and replace bromine, or remove a proton and help form a carbon-carbon double bond. This lesson is about seeing exactly why both routes are...
3.3.3.3 - Ozone DepletionOzone high in the atmosphere is one of the few cases where a reactive substance is clearly helpful. In this lesson, you will see why stratospheric ozone protects life from ultraviolet radiation, how CFCs release chlorine radicals in the upper atmosphere, and why one chlorine radical can help dest...

3.3.4 - Alkenes

3.3.4.1 - Structure, Bonding and Reactivity (Alkenes)Alkenes matter because one small structural change, a carbon-carbon double bond, makes them behave very differently from alkanes. In this lesson, you will pin down exactly what "unsaturated" means, what the double bond is made from, and why that bonding creates a reactive region in the molecule....
3.3.4.2 - Addition Reactions of AlkenesAlkenes are reactive because the carbon-carbon double bond contains a pi bond that is rich in electrons and easy to attack. That makes alkenes especially good at reacting with electron-poor species, so they often undergo electrophilic addition. In this lesson you will follow that pattern through...
3.3.4.3 - Addition PolymersAddition polymers are one of the clearest examples of structure controlling properties. In this lesson, you will learn how alkene monomers become long saturated chains, how to move confidently between monomer and polymer structures, and why these materials are so useful yet so difficult to dispos...

3.3.5 - Alcohols

3.3.5.1 - Alcohol ProductionIndustrial alcohol production is really a choice between two very different routes. One starts with alkenes and adds water across a double bond; the other starts with glucose from plant material and uses yeast enzymes to make ethanol. In this lesson, you will compare those routes, justify the con...
3.3.5.2 - Oxidation of AlcoholsOxidation of alcohols is one of those topics where a small change in structure leads to a very different reaction outcome. In this lesson, you will classify alcohols, choose the correct oxidation product, and see why the method changes the product for a primary alcohol. You will also recognise ho...
3.3.5.3 - Elimination (Alcohols)Alcohols can be turned into alkenes by losing water. That gives us a useful synthetic step because an alkene contains a reactive C=C bond, so it can then be used in addition polymerisation. In this lesson, the focus is on tracking exactly which atoms are removed and seeing how the acid-c...
Required practical 5 - Cyclohexene Preparation and DistillationThis required practical uses the preparation of cyclohexene from cyclohexanol to show how a product can be removed from a reaction mixture by distillation. The chemistry is not just about following a method: you need to understand why cyclohexene leaves first, how the apparatus is arranged safely...

3.3.6 - Organic analysis

3.3.6.1 - Test-Tube Tests for Functional GroupsIdentifying an unknown organic compound often starts with simple reagent tests rather than a full structural analysis. Each test looks for a characteristic kind of reactivity, such as decolourising bromine water, being oxidised, releasing carbon dioxide, or forming halide ions. In this lesson, yo...
Required practical 6 - Organic Functional-Group TestsOrganic molecules can look similar, so chemists often identify them by how they react with carefully chosen reagents. In this required practical, the aim is not to measure an amount but to link a visible observation to a functional group. By the end of the lesson, you should be able to choose sui...
3.3.6.2 - Mass SpectrometryMass spectrometry is especially useful when a chemist needs the molecular formula of an unknown compound. The key idea here is that a high-resolution mass spectrometer measures the mass of the molecular ion so precisely that formulae with the same rounded Mr can still be told apart. We can then...
3.3.6.3 - Infrared SpectroscopyInfrared spectroscopy is useful because it turns invisible bond vibrations into evidence we can read. In this lesson, you will learn how to scan an IR spectrum for key absorptions, use the Chemistry Data Sheet or Booklet to suggest functional groups and possible structures, use the fingerprint re...

3.3.9 - Carboxylic acids and derivatives

3.3.9.1 - Carboxylic Acids and EstersCarboxylic acids and esters are closely linked, because one can be turned into the other. This lesson focuses on how to recognise their structures, why carboxylic acids behave as weak acids, how esters are made and hydrolysed, and how the same chemistry explains fats, soaps, and biodiesel.
3.3.9.2 - AcylationAcylation is the chemistry of transferring an acyl group, RCO-, onto another molecule. In this topic, acyl chlorides and acid anhydrides are the key acylating agents, and the key ideas are recognising their structures, predicting their products with different nucleophiles, and outl...
Required practical 10 - Organic Purification and PurityRequired Practical 10 is really about control and separation. The starting reaction can vary, but the core chemistry stays the same: make the product, remove impurities without losing too much of it, and then use a physical property to judge how pure it is. Once the purpose of each stage is clear...

3.3.11 - Amines

3.3.11.1 - Preparation of AminesAmines are made by introducing an amino group into an organic molecule, but the route you use depends on the starting material. This lesson centres on three distinct preparation routes: halogenoalkane + ammonia, nitrile reduction, and nitro compound reduction. Once those routes feel like three di...
3.3.11.2 - Amines as BasesAmines behave like ammonia because the nitrogen atom has a lone pair that can bond to a proton. The key question in this topic is not just whether they are bases, but how the availability of that lone pair changes from one compound to another. By the end of the lesson, you should be able to expla...
3.3.11.3 - Nucleophilic Properties (Amines)This lesson is about what the lone pair on nitrogen lets ammonia and amines do. You will see how that lone pair allows them to attack electron-poor carbon atoms in two different situations: halogenoalkanes, where the result is nucleophilic substitution, and acyl chlorides or acid anhydrides, wher...

3.3.13 - Amino acids, proteins and DNA

3.3.13.1 - Amino AcidsAmino acids are unusual because one part of the molecule can behave like an acid while another part can behave like a base. In this lesson, you will learn why that happens, why amino acids often exist as zwitterions, and how to draw the structures present in acidic and alkaline solutions without...
3.3.13.2 - ProteinsProteins are built from amino acids, but the interesting part is what happens next: those amino acids join into chains, fold into specific shapes, and can be broken back down and analysed. This lesson keeps those ideas connected so that peptide formation, protein structure, hydrolysis, and chroma...
3.3.13.3 - EnzymesEnzymes matter because they let living systems run essential reactions quickly and selectively under mild conditions. In this lesson, you will see why enzymes are proteins, how an active site helps catalysis happen, why some enzymes only bind one enantiomer, and how a drug can block an enzyme by...
3.3.13.4 - DNADNA is the molecule that stores genetic information, but in this chemistry lesson the focus is on structure and bonding. The key idea is that a simple monomer, the nucleotide, can build a long polymer chain and then form a second matching strand through hydrogen bonding. Once you see how the bond...
3.3.13.5 - Action of Anticancer DrugsCisplatin is a coordination complex that shows how chemistry can be used to treat disease. In this lesson, you will see why its exact shape matters, how it reacts with DNA, and why the same chemistry that helps kill cancer cells can also damage healthy tissue. That balance between benefit and har...