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
How the atomic model changed, and the structure of the atom
- 3 things to know
- Paper 3
Overview
How 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.
What you need to know
Answer each one before you reveal it.
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Key term
Describe the plum pudding model of the atom.
Key term
What two results of the alpha scattering experiment were unexpected?
Questions from this subtopic
Each one with the model answer underneath.
- 1
How did Dalton describe the atom?
Model answer
As a tiny solid sphere that could not be broken down, with all the atoms of a particular element being identical.
- 2
Which particle did Thomson discover, and what did its discovery show about the atom?
Model answer
He discovered the electron, which showed that atoms contain even smaller, negatively charged particles and so are not indivisible.
- 3
Describe the plum pudding model of the atom.
Model answer
The atom was pictured as a ball of positive charge with tiny negative electrons scattered through it.
- 4
Describe the experiment carried out by Geiger and Marsden.
Model answer
They fired alpha particles at a very thin sheet of gold foil and recorded the directions in which the particles travelled afterwards.
- 5
What two results of the alpha scattering experiment were unexpected?
Model answer
Most of the alpha particles passed straight through the foil, but a very small number were deflected through large angles or bounced straight back.
- 6
Explain how Rutherford interpreted the results of the alpha scattering experiment.
Model answer
He concluded that an atom is mostly empty space with its positive charge and nearly all its mass concentrated in a tiny nucleus at the centre.
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