Key term
AQA GCSE Combined Science Chemistry 8464
Atomic Structure and the Periodic Table
Topic overviewAtoms, elements and compoundsWord equations, symbols and balanced equationsMixturesFrom the plum pudding model to the nuclear modelBohr, Chadwick and the modern model of the atomRelative electrical charges of subatomic particlesSize and mass of atomsRelative atomic mass and electronic structureThe periodic tableDevelopment of the periodic tableMetals and non-metalsGroup 0Group 1Group 7
Bonding, Structure, and the Properties of Matter
Topic overviewChemical bonds, including metallic bondingIonic bondingIonic compoundsCovalent bonding and how it is representedThe three states of matter and changes of statePredicting state, state symbols, and the limits of the particle modelProperties of ionic compoundsProperties of small moleculesPolymers and giant covalent structuresProperties of metals and alloys, and why metals conductDiamond and graphiteGraphene and fullerenes
Chemical Analysis
Chemical Changes
Topic overviewThe reactivity seriesMetal oxides, extraction, and redox in terms of electronsAcids reacting with metals, neutralisation and saltsSoluble saltsThe pH scale and neutralisationStrong and weak acidsThe process of electrolysis, and molten ionic compoundsUsing electrolysis to extract metalsElectrolysis of aqueous solutionsRepresentation of reactions at electrodes as half equations
Chemistry of the Atmosphere
Topic overviewThe Earth's early atmosphereHow oxygen increased and carbon dioxide decreasedThe gases in today's atmosphere, and which are greenhouse gasesHuman activities which contribute to an increase in greenhouse gases in the atmosphereGlobal climate change and carbon footprintsAtmospheric pollutants from fuels, and their effects
Energy Changes
Organic Chemistry
Quantitative Chemistry
The Rate and Extent of Chemical Change
Topic overviewMeasuring the mean rate of a reactionRate from graphs, and the gradient of a tangentFactors which affect the rates of chemical reactionsCollision theory and activation energyCatalystsReversible reactions and dynamic equilibriumThe effect of changing conditions on equilibriumThe effect of changing concentrationThe effect of temperature changes on equilibriumThe effect of pressure changes on equilibrium
Chemical Analysis
Pure substances
- 3 things to know
- Chemistry Paper 2
Overview
The chemical meaning of a pure substance, why pure substances melt and boil at fixed temperatures while mixtures change state over a range, using melting and boiling points to test purity, and the everyday meaning of pure compared with the chemist's.
What you need to know
Answer each one before you reveal it.
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Key term
What is the difference between the way a pure compound changes state and the way a mixture does?
Key term
State the measurement you would take to check whether a solid sample is pure.
Questions from this subtopic
Each one with the model answer underneath.
- 1
In chemical terms, what is meant by a pure substance?
Model answer
A pure substance is a single element or a single compound with nothing else mixed into it.
- 2
A sample contains molecules of one compound and nothing else. Is it pure in the chemical sense?
Model answer
Yes, because it is a single compound that is not mixed with any other substance.
- 3
Why is filtered sea water not a pure substance to a chemist?
Model answer
It is still a mixture of water and dissolved salts, so it is not a single element or compound.
- 4
What is the difference between the way a pure compound changes state and the way a mixture does?
Model answer
A pure compound melts and boils at specific fixed temperatures, while a mixture melts and boils over a range of temperatures.
- 5
State the measurement you would take to check whether a solid sample is pure.
Model answer
Measure its melting point and compare it with the accepted melting point of the pure substance.
- 6
Explain why a pure element melts at one sharp temperature.
Model answer
All of its particles are identical, so they all need the same amount of energy to break free at the same temperature.
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