chemical changes

• Metal oxides


  Metals + oxygen -> metal oxides
• Oxidation


  Gain of oxygen
• Reduction


  Loss of oxygen
• Reactivity series


  • When metals react with other substances, metal atoms form positive ions
  • Reactivity of a metal is related to its tendency to form positive ions
  • Metals can be arranged in order of their reactivity in a reactivity series
• Metals in order of reactivity

  • Potassium
  • Sodium
  • Lithium
  • Calcium
  • Magnesium
  • Zinc
  • Iron
  • Copper
• Reactions of metals with water

  • Potassium: violent
  • Sodium: very quick
  • Lithium: quick
  • Calcium: more slow
• Reactions of metals with dilute acid

  • Calcium: very quick
  • Magnesium: quick
  • Zinc: fairly slow
  • Iron: more slow
  • Copper: very slow
• Non-metals hydrogen and carbon are often included in the reactivity series
• Displacement


  A more reactive metal can displace a less reactive metal from a compound
• Gold is very unreactive and is found in the Earth as the metal itself
• Most metals are found as compounds that require chemical reactions to extract the metal
• Reduction


  Involves the loss of oxygen
• Oxidation


  Loss of electrons
• Reduction


  Gain of electrons
• Writing ionic equations


  1. If sodium is oxidised, it has lost an electron, leaving it with a +1 charge, so the ionic equation is: Na -> Na+ + e-

  2. If sodium +1 ion is reduced, it has gained an electron, leaving it with a charge of zero, so the ionic equation is: Na+ + e- -> Na

  3. The charges on each side of the equation should add up to the same number
• Identifying oxidation and reduction in an equation

  1. e.g. 2Na + 2HCl -> 2NaCl + H2

  2. HCl is made up of H+ and Cl- ions & NaCl is made up of Na+ and Cl- ions

  3. Looking at just sodium: 2Na -> 2Na+, so the ionic equation must be: 2Na -> 2Na+ + 2e-, meaning sodium has lost electrons & has been oxidised

  4. Looking at just chlorine: 2Cl- -> 2Cl-, meaning chlorine has not been oxidised or reduced

  5. Looking at just hydrogen: 2H+ -> H2, so the ionic equation must be: 2H+ + 2e- -> H2, meaning hydrogen has gained electrons so has been reduced