C2 1

C2 1.1

•   Element – a substance made from only one type of atom.
  •  It cannot be broken down into simple substances.
  •  All elements are listed in the periodic table.
• Compound - a substance made from different elemnets chemically joined together.
  • The properties of a compound are different to those of the elements from which it was made.
  • Compounds can be docomposed (broken down) int simpler substances. This can be achieved by:
    • heating (thermal decomposition).
    • Electricity (electrolysis) - passing a current through the substance.
• Properties of each substance in a mixture are the same as before they were mixed.

C2 1.2

• Noble gases
  • Found in group 0 of the periodic table.
  • Do not join in any reactions at all - very unreactive
  • They are very stable because they have full outer electron shells (energy levels).
• Atoms are made of:
  • A central nucleus - containing protons and neutrons.
  • Electrons circling the nucleus in different energy levels
    • Energy levels acn only take a certain number of electrons:
      • First energy level - up to 2 electrons
      • Second energy level - up to 8 electrons
      • Third energy level - up to 8 electrons
• Other less stable elements take part in chemical reactions to gain a full outer energy level. To do this they will:
  • Give away electrons to other elements to lose an energy level and move down to a full one.
  • Take electrons from other elements to fill their outer energy level.
• Electrons, protons and neutrons all ahve different charges:
  • Protons have a positive charge +
  • Electrons have a negative charge -
  • Neutrons have no charge 0
• If an atom:
  • Loses an electron it now has one more proton than electrons and a single positive charge. It is called an ion
  • Gains an electron it now has one more electron than protons and a single negative charge. It is now an ion.
    • Negative ions are called halide ions.
• All…