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Key concepts in chemistry

Edexcel GCSE ChemistryTopic 1 of 953 lessons

Revision notes for Key concepts in chemistry in Edexcel Chemistry (1CH0). Every lesson in BrainCake comes with R.E.C.I.P.E. recall steps, a quick check and spaced reviews.

  1. How the model of the atom has changedIn about 1800 John Dalton pictured atoms as tiny solid spheres.
  2. The structure of an atomAn atom has a very small nucleus at its centre.
  3. Relative charge and relative mass of subatomic particlesThe three particles in an atom are compared using relative charge and relative mass.
  4. Why atoms have equal numbers of protons and electronsAn atom has no overall electric charge, so we say it is electrically neutral.
  5. The size of the nucleusThe nucleus is very small compared with the overall size of an atom.
  6. Where the mass of an atom is concentratedMost of the mass of an atom is concentrated in the nucleus, even though the nucleus is tiny.
  7. Mass numberAn atom has a tiny nucleus made of protons and neutrons, with electrons in shells around it.
  8. Atoms of an element and the proton numberEvery atom of a given element has the same number of protons in its nucleus.
  9. IsotopesAtoms of the same element always have the same number of protons, but they can have different numbers of neutrons.
  10. Protons, neutrons and electrons in atomsThe nuclear symbol of an atom shows two numbers.
  11. Isotopes and relative atomic massThe relative atomic mass (Ar) of an element compares the mass of its atoms with the mass of other atoms.
  12. Calculating relative atomic massTo calculate the relative atomic mass (Ar) of an element, multiply the mass of each isotope by its abundance, add the results, and divide by the…
  13. How Mendeleev arranged the elementsIn 1869 the Russian chemist Dmitri Mendeleev tried to bring order to the elements that were known at the time.
  14. How Mendeleev predicted undiscovered elementsWhen Mendeleev arranged the elements, some did not fit the pattern.
  15. Why relative atomic mass did not always workMendeleev thought he had arranged the elements in order of increasing relative atomic mass.
  16. Atomic numberEvery atom has a nucleus containing protons and neutrons.
  17. Periods and groupsIn the modern periodic table the elements are arranged in order of increasing atomic number.
  18. Metals and non-metalsMost elements are metals.
  19. Electronic configurations of the first 20 elementsThe electrons in an atom are arranged in shells, also called energy levels.
  20. Electronic configuration and position in the periodic tableAn element's electronic configuration tells you where it sits in the periodic table.
  21. Ionic bonding and dot and cross diagramsAn ionic bond forms between a metal atom and a non-metal atom when electrons are transferred from one atom to the other.
  22. IonsAn ion is an atom or group of atoms with a positive or negative charge.
  23. Protons, neutrons and electrons in ionsThe atomic number of an element is its number of protons.
  24. Formation of ions in ionic compounds (Groups 1, 2, 6 and 7)Atoms form ions so that they have a full outer shell of electrons.
  25. The endings -ide and -ateThe name of a compound tells you which elements it contains.
  26. Formulae of ionic compoundsAn ionic compound has no overall charge.
  27. Ionic compounds as latticesAn ionic compound is not made of separate molecules.
  28. How a covalent bond formsA covalent bond forms when two atoms share a pair of electrons.
  29. Covalent bonding and moleculesWhen atoms of non-metals join by covalent bonds, they form molecules.
  30. The size of atoms and moleculesAtoms are extremely small.
  31. Dot and cross diagrams for simple moleculesA covalent bond forms when two atoms share a pair of electrons.
  32. Types of substanceSubstances can be sorted into four types by their structure and bonding.
  33. Properties of ionic compoundsAn ionic compound is a giant lattice of positive and negative ions.
  34. Properties of simple molecular compoundsA typical covalent, simple molecular compound is made of small molecules.
  35. Graphite and diamondGraphite and diamond are different forms of carbon.
  36. Structures of graphite and diamondIn diamond each carbon atom forms four covalent bonds to four other carbon atoms.
  37. Uses of graphite and diamondGraphite and diamond are both giant covalent forms of carbon, but their different structures give them very different uses.
  38. Fullerenes and grapheneFullerenes are molecules made only of carbon atoms joined in rings, forming hollow shapes such as spheres and tubes.
  39. Poly(ethene) as a polymerA polymer is a very large molecule made of many small molecules joined together in a long chain.
  40. Properties of metalsA metal is a giant structure.
  41. Limitations of modelsChemists use models and diagrams to represent structures, but every one has limitations.
  42. Metals and non-metalsMost metals have a similar set of physical properties.
  43. Relative formula mass and percentage by massThe relative formula mass (Mr) of a substance is found by adding up the relative atomic masses (Ar) of all the atoms in its formula.
  44. Formulae from reacting masses or percentagesAn empirical formula shows the simplest whole-number ratio of the atoms of each element in a compound.
  45. Empirical and molecular formulaeA molecular formula shows the actual number of atoms of each element in one molecule.
  46. Experiment to find the empirical formula of magnesium oxideYou can find the formula of magnesium oxide by measuring the masses of magnesium and oxygen that combine.
  47. Conservation of massThe law of conservation of mass says that no mass is lost or gained in a chemical reaction, so the total mass of the reactants equals the total mass…
  48. Calculating reacting massesYou can use a balanced equation to calculate the mass of a product or reactant when you are given the mass of just one substance.
  49. Calculate the concentration of solutions in g dm–3When a solid solute dissolves in water, the mixture is a solution.
  50. The mole and the Avogadro constantAtoms, molecules and ions are far too small to count one at a time, so chemists count them in large batches called moles.
  51. Moles, mass and number of particlesThe number of moles of a substance can be found from its mass.
  52. Limiting reactants and the mass of productIn many reactions one reactant is deliberately or accidentally used in a larger amount than is needed.
  53. Deducing the stoichiometry of a reactionThe stoichiometry of a reaction is the ratio in which the substances react and form.

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