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• Atoms contain a nucleus which contains protons and neutrons.
• Electrons orbit the nucleus in electron shells.
• Electrons are negatively charged.
• The nucleus has a positive charge as the protons cancel out the neutrons
• Protons have a relative mass of 1 with a relative charge of +1
• Neutrons have a relative mass of 1 with a relative charge of 0.
• Electrons have a very small relative mass and a relative charge of -1.
• Atoms are neutral due to them having the same number of protons and electrons.
• An ion is an atoms that has lost or gained electrons.
• An element is a substance made up of atoms that all have the same number of protons in their nucleus.
• Isotopes are the same elements with the same amount of protons but different number of neutrons.
• A example of isotopes are carbon-12 and carbon-13.
• When elements react, atoms combine with other atoms to form compounds.
• A compound is a substance made from two or more different elements that are chemically bonded together.
• the ph scale is a measure of how acidic or alkaline a solution s
• the lower the ph the more acidic
• a neutral substance has ph 7
• an indicator is a dye that changes colour depending on its ph
• a ph probe is an electronic ph measurer
• acids and bases neutralise each other
• an acid is a substance that forms aqueous solutions with a ph less than 7
• acids form h+ ions in water.
• a base is a substance with a ph greater than 7 (alkali)
• an alkali is a base that dissolves in water to form a solution with a ph greater than 7.
• Alkalis form OH- ions in water
• Ionic compounds


  Can conduct electricity when molten or dissolved in water
• Solid ionic compounds cannot conduct electricity
• Solid ionic compounds


  • Ions are locked in place, not free to move
  • Held in place by strong electrostatic forces of attraction
• Molten/dissolved ionic compounds


  • Forces of attraction are broken, ions are free to move
  • These liquids/solutions are called electrolytes
• Electrolysis of molten ionic compound (e.g. lead bromide)

  1. Positive lead ions attracted to negative electrode (cathode)

  2. Lead ions gain 2 electrons to form lead atoms (reduction)

  3. Negative bromide ions attracted to positive electrode (anode)

  4. Bromide ions lose 1 electron to form bromine atoms (oxidation)

  5. Bromine atoms pair to form bromine molecules
• Bromine atoms pair to form bromine molecules
• Electrolysis can be used to extract reactive metals like aluminium
• Electrolysis


  Used to extract some metals
• Extracting aluminium by electrolysis

  1. Mix aluminium oxide with compound cryolite to lower melting point

  2. Apply electric current to molten aluminium oxide

  3. Aluminium ions attracted to cathode and gain 3 electrons to form aluminium atoms

  4. Oxide ions attracted to anode and lose 2 electrons to form oxygen atoms
• Anode in aluminium extraction

  • Made of graphite, a form of carbon
  • Oxygen molecules produced react with graphite to form carbon dioxide gas, requiring regular replacement of anode
• Producing metals by electrolysis is very expensive
• Reasons electrolysis is expensive

  • Melting the compounds like aluminium oxide requires a great deal of energy
  • Producing the electric current requires a lot of energy
• Half-equations for cathode and anode reactions in aluminium extraction


  1. Cathode: Al3+ + 3e- → Al (aluminium ion gains 3 electrons to form aluminium atom)

  2. Anode: 2O2- → O2 + 4e- (oxide ion loses 2 electrons to form oxygen molecule)
• Aqueous solution


  Dissolved in water
• Ionization of water


  Water molecules split to form hydrogen ions and hydroxide ions