Paper 1 topics

• Element

  Made up of only one type of atom
• Compound

  Made up of more than one type of atom bonded together
• Chemical reaction

  1. Formation of one or more new substances

  2. Often involves an energy change
• Word equation


  Represents a chemical reaction using words
• Formula equation


  Represents a chemical reaction using chemical formulas
• Mixture

  Two or more elements or compounds not chemically combined together
• Separation techniques for mixtures

  • Filtration
  • Crystallisation
  • Simple distillation
  • Fractional distillation
  • Chromatography
• Pure substances melt at an exact temperature, mixtures melt over a range of temperatures
• Chemists can tell a pure substance from a mixture by its melting point
• Dalton model of the atom

  Atoms are tiny spheres that cannot be divided into anything smaller
• Thompson's "Plum Pudding" model of the atom

  Atoms are like balls of positive charge with negative electrons stuck in them
• Rutherford's model of the atom

  Atom is mostly empty space with a tiny, dense, positively charged centre (the nucleus)
• Evidence for the nucleus in Rutherford's experiment: While most alpha particles passed straight through the gold foil, some "deflected" off something small and positive (the nucleus)
• Bohr model of the atom

  Electrons exist at set energy levels (electron shells)
• Chadwick's nuclear model of the atom

  Includes the discovery of the neutron
• Current model of the atom

  Nuclear model
• What Rutherford's alpha scattering experiment proved

  • Atoms are mostly empty space
  • Atoms have a tiny, dense, positively charged centre (the nucleus)
  • Atoms can be split
• The nucleus of an atom is absolutely tiny compared to the whole atom, with a radius of approx. 1 x 10-14 m
• Proton

  Positive charge, small relative size, located in the nucleus
• Neutron

  No charge, small relative size, located in the nucleus
• Electron

  Negative charge, small relative size, located outside the nucleus
• Atomic radius

  Approx. 0.1 nm (1 x 10-10 m)
• Nuclear radius

  Approx. 1 x 10-14 m
• Atomic number


  The number of protons in an atom's nucleus
• Mass number

  The total number of protons and neutrons in an atom's nucleus
• Isotope

  An atom with a different number of neutrons but the same number of protons
• Calculating relative atomic mass (Ar) from isotopes


  1. Ar = average mass of the isotopes

  2. Ar = (mass of isotope 1 x abundance) + (mass of isotope 2 x abundance) + ...
• Relative atomic mass (Ar)

  The average mass of an element's isotopes
• Relative formula mass (Mr)

  The sum of all the relative atomic masses in a compound
• Most elements have isotopes, so the atomic mass you see on the periodic table is an average mass of those isotopes
• Mendeleev arranged elements based on their properties and atomic weight, leaving gaps to make the pattern fit
• Elements are arranged in the periodic table by increasing atomic (proton) number, not atomic weight
• Group (column)

  Tells you the number of electrons in an atom's outer shell
• Period (row)

  Tells you the number of electron shells an atom has
• Non-metals are found on the right side of the periodic table
• Mendeleev used the properties of elements above and below missing elements to predict their properties
• First electron shell

  Max 2 electrons
• Second and third electron shells

  Max 8 electrons each
• Properties of group 0 (noble gases)

  • Inert (unreactive)
  • Colourless
  • Odourless
• Helium is an exception with only 2 electrons in its outer shell