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
Carbon's four bonds, and the variety of organic compounds
- 3 things to know
- Paper 1
Overview
Why a carbon atom forms four covalent bonds and never five, how many bonds remain after a double bond, why carbon forms so many compounds in chains, branches and rings, homologous series such as the alkanes, ring structures, compounds with the same formula but different properties, and natural and synthetic organic compounds.
What you need to know
Answer each one before you reveal it.
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Key term
If a carbon atom forms a double bond to another atom, how many further bonds can it still make?
Key term
In a long chain of carbon atoms, how many bonds does each carbon atom make in total?
Questions from this subtopic
Each one with the model answer underneath.
- 1
How many covalent bonds can a single carbon atom form?
Model answer
It can form four.
- 2
Why is a carbon atom able to form four covalent bonds?
Model answer
Because it has four electrons in its outer shell and needs four more to fill it, so it can share four pairs.
- 3
How many hydrogen atoms bond to one carbon atom in methane, and why that number?
Model answer
Four, because each hydrogen shares one pair of electrons with the carbon and this uses up all four of the carbon's bonds.
- 4
If a carbon atom forms a double bond to another atom, how many further bonds can it still make?
Model answer
Two, because the double bond uses two of its four bonds.
- 5
Why can a carbon atom never form five bonds?
Model answer
Because it has only four outer shell electrons available to share, so only four shared pairs can be made.
- 6
In a long chain of carbon atoms, how many bonds does each carbon atom make in total?
Model answer
Four in total, shared between the neighbouring carbon atoms and other atoms such as hydrogen.
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