4. Chemical Changes

• Metal oxides

  Metals can react with oxygen to form metal oxides
• Formation of metal oxides

  1. Oxidation reaction

  2. Oxygen is added to the metal
• Loss of oxygen from metal oxides


  Reduction reaction
• Reactivity series of metals

  Metals placed in order of reactivity based on their reactions with acids and water
• Reactivity of metals

  • Metals lose electrons and form positive ions when they react with another element
  • The greater the tendency to lose electrons, the greater the reactivity
• The reactivity series determines the tendency of metals to lose electrons and form positive metal ions
• Metal oxides

  Metals can react with oxygen to form metal oxides
• Formation of metal oxides

  1. Oxidation reaction

  2. Oxygen is added to the metal
• Loss of oxygen from metal oxides

  Reduction reaction
• Reactivity series of metals

  Metals placed in order of reactivity based on their reactions with acids and water
• Reactivity of metals

  • Metals lose electrons and form positive ions when they react with another element
  • The greater the tendency to lose electrons, the greater the reactivity
• Metals reacting with water 

  
• Metals reacting with water 

  Only metals above hydrogen in the reactivity series will react with water. The speed of the reaction depends on how high up the metal is in the reactivity series. Some metals, such as iron, have slow reactions with water, while others like potassium react vigorously with water. 

  Some metals react with cold water to form a metal hydroxide and hydrogen gas:

  sodium + water ⟶  sodium hydroxide + hydrogen

  Other metals react with gaseous water to form a metal oxide and hydrogen gas:

  magnesium + water  ⟶ magnesium oxide + hydrogen
• Metals reacting with acids 

  Only metals above hydrogen in the reactivity series will react with dilute acids. The hydrogen in the acid is replaced by the metal atom to produce a salt and hydrogen gas:

  zinc + hydrochloric acid ⟶  zinc(II) chloride + hydrogen

  
• Reactivity series


  Metals only react with acid if the metal is more reactive than hydrogen
• Carbon in the reactivity series

  Allows us to see whether a metal oxide can be reduced by carbon or not for metal extraction
• Metal Extraction


  • Many metals exist as ores in the Earth's crust
  • Ores are rocks containing enough metal that it is economically worthwhile extracting them
  • Usually, the ore is an oxide of the metal, for example, aluminium oxide
• Methods used to extract metals from their ores

  1. Metals above carbon in the reactivity series are extracted using electrolysis

  2. Metals below carbon in the reactivity series are extracted using carbon as a reducing agent

  3. metal oxide + carbon → metal + carbon dioxide
• Native metals

  • Gold
• Some metals, such as gold, are unreactive and found as an uncombined element so do not need to be chemically extracted
• Displacement reactions

  Occur when a more reactive metal takes the place of a less reactive metal in one of its compounds
• Displacement reactions

  • zinc + copper oxide → zinc oxide + copper
  • Mg + CuSO4 → MgSO4 + Cu
• Zinc, which is higher up the reactivity series than copper, displaces the copper from its oxide
• Displacement also occurs between metals and aqueous solutions of metal salts
• Copper(II) sulfate solution is blue
• As the magnesium displaces the copper in the compound

  The blue colour will fade as the magnesium sulfate solution forms, which is colourless
• Oxidation & Reduction in Terms of Electrons

  
• Displacement


  Electrons are lost and gained
• Oxidation


  Loss of electrons
• Reduction

  Gain of electrons
• Writing ionic equations and half equations for displacement reactions


  1. Write word equation

  2. Identify ions involved

  3. Remove spectator ions

  4. Identify oxidation and reduction half equations
• Displacement of copper in copper sulfate by magnesium

  Magnesium + copper sulfate → magnesium sulfate + copper
• The ions involved in the equation are: Mg (s) + Cu2+ (aq) + SO42- (aq) → Mg2+ (aq) + SO42- (aq) + Cu (s)
• Writing the ionic equation

  Mg (s) + Cu2+ (aq) → Mg2+ (aq) + Cu (s)
• Writing the half equations

  1. Mg → Mg2+ + 2e-

  2. Cu2+ + 2e- → Cu
• Oxidation


  Magnesium atoms lose electrons
• Reduction

  Copper ions gain electrons
• What keyword definitions do I need to know for the reactivity of metals? 

  Some keyword definitions you need to know are:

  • Oxidation - the gain of oxygen and loss of electrons
  • Reduction - the loss of oxygen and gain of electrons
  • Redox - oxidation and reduction occurring simultaneously
  • Displacement - a more reactive element takes the place of a less reactive element 

  This is a quick summary of some key concepts on the reactivity of metals - remember to go through the full set of revision notes, which are tailored to your specification, to make sure you know everything you need for your exams!
• Reactivity Series of Metals

  Based on how they react with other substances, a series can be produced in which the metals are placed in order of their reactivity
• Metal atoms

  Form positive ions by loss of electrons when they react with other substances