Key term
OCR GCSE Chemistry A J248
Chemical Reactions
Topic overviewWriting formulae of elements and compoundsBalanced equations, and deducing formulae from ionsIonic equations, and state symbolsThe mole and the Avogadro constantConservation of mass, and changes of mass in open systemsStoichiometry, and calculating reacting massesExothermic and endothermic reactions, and reaction profilesActivation energy, and bond energy calculationsOxidation and reduction, by oxygen and by electronsAcids, alkalis and neutralisationThe ionic equation for neutralisation, and reactions of acidsDilute and concentrated, weak and strongThe pH scale, and hydrogen ion concentrationpH as a factor of ten, and measuring pHProducts at the electrodes, and molten ionic compoundsElectrolysis of aqueous solutionsInert and non-inert electrodes
Elements, Compounds and Mixtures
Topic overviewPurity, and melting point dataRelative formula mass and empirical formulaeFormulations, and separating mixturesPaper and thin layer chromatographyInterpreting chromatograms and Rf valuesChoosing a purification methodMetals and non-metals in the Periodic TableElectron arrangement and position in the Periodic TableIonic, covalent and metallic bonding comparedDot and cross diagrams, and the limits of modelsReactions, electron arrangement and Mendeleev's tableCarbon's four bonds, and the variety of organic compoundsDiamond, graphite, fullerenes and grapheneBond strength, intermolecular forces and predicting stateBulk properties of ionic, molecular and giant structuresNanoparticles: size and surface area to volumeUses and risks of nanoparticulate materials
Global Challenges
Topic overviewExtracting metals by reduction and by electrolysisBiological methods of metal extractionRate against yield in industry, and reaction conditionsThe Haber process and fertiliser productionNitrogen, phosphorus and potassium in agricultureLife cycle assessmentRecycling, and the decisions behind itAlloys, and the corrosion of metalsComparing glass, ceramics, polymers, composites and metalsFunctional groups and homologous seriesPredicting the products of organic reactionsAddition polymerisationCondensation polymerisation, and making a polymerDNA and other natural polymersFractional distillation of crude oilThe fractions, and crude oil as a feedstockDependence on hydrocarbons, and crackingChemical cells and fuel cellsThe Earth's early atmosphere, and how oxygen developedThe greenhouse effect, and evidence for climate changeEffects of carbon dioxide and methane, and air pollutantsProducing potable water
Monitoring and Controlling Chemical Reactions
Topic overviewConcentration in mol/dm³, and titrationTitration calculations, and the mass of a soluteMolar gas volume and the volumes of gasesTheoretical mass and percentage yieldAtom economy, and choosing a reaction pathwayMeasuring the rate of a reaction, and rate graphsFactors affecting rate, and collision theorySurface area and rateCatalysts and how they workReversible reactions and dynamic equilibriumChanging the conditions of an equilibriumActivation energy, and enzymes as catalysts
Particles
Predicting and Identifying Reactions
Topic overviewGroups 1, 7 and 0, and why they behave as they doTransition metalsPredicting reactivity from the Periodic TableReactivity of metals with water and acidsTests for oxygen, hydrogen, carbon dioxide and chlorineTests for aqueous cations and anionsFlame tests, and identifying metal ionsIdentifying a species from test resultsInstrumental methods of analysis
Particles
- 5 subtopics
- 15 things to know
- Paper 3
What Particles covers
Particles is examined in Chemistry A Paper 3. It covers the particle model and changes of state; limitations of the particle model; how the atomic model changed and the structure of the atom; the size of atoms and the subatomic particles; and calculating protons, neutrons and electrons.
Where it is assessed
Paper 3
Chemistry A Paper 3: 1 hour 45 minutes, 90 marks, 50% of the GCSE.
Check the OCR specification ↗The 5 subtopics
Each one has its own page.
- The particle model and changes of stateWhat the particle model assumes, the arrangement and movement of particles in solids, liquids and gases, melting, freezing, boiling, condensing and sublimation, why melting needs energy and gases compress, what physical and chemical changes are and how to tell them apart, why melting, freezing and dissolving salt are physical while burning magnesium is chemical, and why physical changes reverse easily.Open →
- Limitations of the particle modelHow the simple model pictures particles as solid spheres, the forces, size differences and spacing it leaves out, why real atoms are not solid, why it cannot explain condensing, and why it is still useful.Open →
- How the atomic model changed, and the structure of the atomHow the model of the atom developed from Dalton's solid sphere through Thomson's electron and plum pudding model, Geiger and Marsden's alpha scattering experiment and Rutherford's nucleus to Bohr's shells and Chadwick's neutron, why models change with new evidence, and the structure of the atom: its charged nucleus, its tiny size, where its mass lies, and why it is neutral and mostly empty space.Open →
- The size of atoms, and the subatomic particlesThe typical radius of an atom and length of a bond, writing sizes in standard form, comparing a nucleus, an atom and a small molecule, the relative charges and masses of protons, neutrons and electrons, where each is found, why electron mass is ignored and atoms are neutral, and the symbols ~, <, >, << and >>.Open →
- Calculating protons, neutrons and electronsWhat atomic number and mass number are, working out the number of neutrons, what isotopes and ions are, where the two numbers are written beside a symbol, and counting the protons, neutrons and electrons in an atom and in chloride and magnesium ions.Open →
What you need to know
Answer each one before you reveal it.
Your recallNot started
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Name the changes of state between solid, liquid and gas, and explain why a gas can be compressed but a solid cannot.
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How does the simple particle model picture particles, what property is left out, and why does leaving out forces make boiling points hard to explain?
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How did Dalton describe the atom?
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Write the length 0.000 000 000 1 m in standard form.
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What is the atomic number of an element?
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In the simple particle model, how are the particles pictured?
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Describe the plum pudding model of the atom.
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An atom has a radius of 1 × 10⁻¹⁰ m. What is its diameter?
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What is the mass number of an atom?
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Name the change of state in which a solid becomes a liquid, and the reverse change.
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State one important property of real particles that is ignored when they are drawn as solid spheres.
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What two results of the alpha scattering experiment were unexpected?
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Put a nucleus, a whole atom and a small molecule in order of increasing size.
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What are isotopes?
Take Particles further
The same content, four other ways.
Commonly confused
Pairs that lose marks when they are blurred together.
Physical change vs Chemical change
Physical change: no new substance forms and the particles are unchanged. Chemical change: atoms rearrange to form one or more new substances.
Atomic number vs Mass number
Atomic number: how many protons the nucleus contains. Mass number: total protons plus neutrons in the nucleus.
Proton vs Neutron
Proton: nuclear particle with relative charge +1 and relative mass 1. Neutron: uncharged nuclear particle with relative mass 1, discovered by Chadwick.
Questions from this topic
Each one with the model answer underneath.
- 1
What does the particle model assume about the particles that make up a substance?
Model answer
It assumes that all substances are made of tiny particles that are constantly moving and are attracted to one another.
- 2
Describe the arrangement and movement of the particles in a solid.
Model answer
They are packed closely together in a regular arrangement and vibrate about fixed positions.
- 3
Describe the arrangement and movement of the particles in a liquid.
Model answer
They are still close together but arranged randomly, and they move around and slide past one another.
- 4
Describe the arrangement and movement of the particles in a gas.
Model answer
They are far apart and arranged randomly, and they move quickly in all directions.
- 5
Name the change of state in which a solid becomes a liquid, and the reverse change.
Model answer
A solid becoming a liquid is melting, and a liquid becoming a solid is freezing.
- 6
Name the change of state in which a liquid becomes a gas, and the reverse change.
Model answer
A liquid becoming a gas is boiling or evaporating, and a gas becoming a liquid is condensing.
What is inside Levo
Six ways to work the same material.
Particles revision questions
- What does Particles cover in OCR GCSE Chemistry A?
- 5 subtopics: the particle model and changes of state, limitations of the particle model, how the atomic model changed, and the structure of the atom, the size of atoms, and the subatomic particles and calculating protons, neutrons and electrons. Each one has its own page with questions and model answers.
- How is Particles organised?
- By the OCR J248 specification, subtopic by subtopic, so it matches the order you are taught it in.
Every question in Particles, on a schedule.
Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.
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