Key term
OCR GCSE Chemistry A J248
Chemical Reactions
Topic overviewWriting formulae of elements and compoundsBalanced equations, and deducing formulae from ionsState symbols in equationsConservation of mass, and changes of mass in open systemsExothermic and endothermic reactions, and reaction profilesActivation energy and why reactions need itOxidation and reduction in terms of oxygenAcids, alkalis and neutralisationThe ionic equation for neutralisation, and reactions of acidsThe pH scale, acidity and alkalinityMeasuring pH with indicators and pH metersProducts 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 electrolysisThe 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 polymerisationDNA 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 overviewCarrying out an acid–alkali titrationTheoretical mass and percentage yieldAtom economy and its calculationMeasuring the rate of a reaction, and rate graphsFactors affecting rate, and collision theorySurface area and rateCatalysts and how they workReversible reactions and dynamic 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
Elements, Compounds and Mixtures
Bond strength, intermolecular forces and predicting state
- 2 things to know
- Paper 1
Overview
Why simple molecular substances melt and boil at low temperatures without breaking covalent bonds, why ionic compounds, giant covalent structures and metals have high melting points, why boiling points rise as molecules get larger, and predicting whether a substance is a solid, liquid or gas at a given temperature from its melting and boiling points.
What you need to know
Answer each one before you reveal it.
Your recallNot started
Key term
Explain why simple molecular substances melt and boil at low temperatures.
Questions from this subtopic
Each one with the model answer underneath.
- 1
What has to happen to the forces between particles before a solid will melt?
Model answer
Enough energy must be transferred to overcome the forces holding the particles in their fixed positions.
- 2
Explain why simple molecular substances melt and boil at low temperatures.
Model answer
Because only the weak intermolecular forces between the molecules have to be overcome, and these need very little energy.
- 3
Are covalent bonds broken when a simple molecular substance boils?
Model answer
No, the molecules stay whole and only the weak forces between them are overcome.
- 4
Explain why ionic compounds have high melting points.
Model answer
Because strong electrostatic attractions act between the oppositely charged ions throughout the lattice, and a great deal of energy is needed to overcome them.
- 5
Explain why giant covalent structures have exceptionally high melting points.
Model answer
Because melting requires many strong covalent bonds running through the whole structure to be broken.
- 6
Explain why most metals have high melting points.
Model answer
Because there is a strong electrostatic attraction between the positive metal ions and the delocalised electrons, which takes a lot of energy to overcome.
Other ways to work this
The same content, four other ways.
What is inside Levo
Six ways to work the same material.
Every question in Elements, Compounds and Mixtures, 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.
Or £46 a year, about £3.83 a month. Cancel anytime.