Elements, compounds and mixtures

OCR GCSE ChemistryTopic 2 of 630 lessons

Revision notes for Elements, compounds and mixtures in OCR Chemistry A (J248). Every lesson in BrainCake comes with R.E.C.I.P.E. recall steps, a quick check and spaced reviews.

1. Purity of a substanceIn everyday life the word pure usually means natural, or with nothing added.
2. Melting point and purityA pure substance melts at one fixed temperature, called its melting point.
3. Relative formula massThe relative atomic mass (Ar) of an element is the weighted mean mass of its atoms compared with one twelfth of the mass of a carbon-12 atom.
4. Empirical formulaeThe empirical formula of a compound shows the simplest whole number ratio of atoms of each element in it.
5. Formulations and alloysA formulation is a mixture that has been designed as a useful product.
6. Separating mixturesThe substances in a mixture are not chemically joined, so a mixture can be separated by physical methods.
7. Paper and thin layer chromatographyChromatography separates a mixture of substances that dissolve in the same solvent.
8. Stationary and mobile phasesEvery type of chromatography has two parts.
9. Interpreting chromatograms and Rf valuesA chromatogram shows each substance as a spot.
10. Choosing a purification techniqueTo choose a purification technique, look at the properties of the substances in the mixture.
11. Using chromatography to test purity and identify substancesChromatography can show whether a substance is pure.
12. Metals and non-metalsMetals and non-metals can be told apart by their physical properties.
13. Atomic structure and position in the Periodic TableThe Periodic Table is arranged in columns called groups and rows called periods.
14. Electron arrangement and the Periodic TableThe elements are arranged in order of atomic number, which is the number of protons in the nucleus of an atom.
15. Ionic, simple molecular and giant covalent bondingIn an ionic compound a metal has transferred electrons to a non-metal, so the compound is made of oppositely charged ions.
16. Electrostatic forces, transfer and sharing of electronsAll chemical bonding can be explained with electrostatic forces.
17. Dot and cross diagramsA dot and cross diagram shows only the electrons in the outer shell of each atom.
18. Limitations of bonding modelsWe cannot see atoms, so scientists use models to represent them.
19. Electron arrangement and the reactions of elementsThe atomic number of an element is the number of protons in the nucleus of its atoms.
20. From Mendeleev's table to the modern Periodic TableIn 1869 Mendeleev arranged the elements in order of atomic mass.
21. Carbon forms four covalent bondsCarbon is in Group 4 of the periodic table, so its atoms have four electrons in their outer shell.
22. Carbon compounds: chains, rings and familiesCarbon forms an enormous number of different compounds.
23. Diamond, graphite, fullerenes and grapheneDiamond, graphite, fullerenes and graphene are all forms of pure carbon, but their structures differ so their properties differ.
24. Energy, bonds and changes of stateWhen a substance melts or boils, energy is transferred to its particles from the surroundings.
25. Using data to predict states of substancesThe state of a substance at a given temperature depends on its melting point and boiling point.
26. Bulk properties of materialsThe bulk properties of a material, such as melting point, hardness and electrical conductivity, come from the way its particles are bonded and…
27. Nano dimensions compared with atoms and moleculesThe prefix 'nano' means a very small size.
28. Surface area to volume ratio and propertiesThe surface area to volume ratio compares the area on the outside of an object with the space inside it.
29. Properties and uses of nanoparticulate materialsNanoparticles have a very large surface area to volume ratio.
30. Risks of nanoparticulate materialsNanoparticles are useful, but their small size can also cause problems.

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