Key term
OCR GCSE Combined Science Chemistry J250
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 structures
Global Challenges
Topic overviewExtracting metals by reduction and by electrolysisBiological methods of metal extractionLife cycle assessmentRecycling, and the decisions behind itFractional distillation of crude oilThe fractions, and crude oil as a feedstockDependence on hydrocarbons, and crackingThe 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 overviewMass of solute, concentration and dilution calculationsMeasuring 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
Particles
The size of atoms, and the subatomic particles
- 3 things to know
- Paper 9 (Chemistry)
Overview
The 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 >>.
What you need to know
Answer each one before you reveal it.
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Key term
An atom has a radius of 1 × 10⁻¹⁰ m. What is its diameter?
Key term
Put a nucleus, a whole atom and a small molecule in order of increasing size.
Questions from this subtopic
Each one with the model answer underneath.
- 1
What is the typical radius of an atom?
Model answer
About 1 × 10⁻¹⁰ m.
- 2
What is the typical length of the bond between two atoms in a small molecule?
Model answer
About 1 × 10⁻¹⁰ m, the same order of magnitude as the radius of an atom.
- 3
Write the length 0.000 000 000 1 m in standard form.
Model answer
1 × 10⁻¹⁰ m.
- 4
An atom has a radius of 1 × 10⁻¹⁰ m. What is its diameter?
Model answer
2 × 10⁻¹⁰ m.
- 5
A row of atoms, each 1 × 10⁻¹⁰ m across, stretches a total length of 1 × 10⁻⁶ m. How many atoms are in the row?
Model answer
10 000 atoms.
- 6
How does the size of a small molecule such as water compare with the size of a single atom?
Model answer
It is of the same order of magnitude, only a few times 10⁻¹⁰ m across.
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