Pure substances

• Pure substance


  Only containing one type of particle - can be pure element or pure compound
• Pure substances


  • Have a single sharp melting and boiling point
• Mixture


  Contains different types of particle
• Mixtures


  • Melt and boil over a range of temperatures
• Chemical test for water

  Anhydrous copper(II) sulphate turns from white to blue
• Chemical test for water

  • Tells you water is present, but not how pure it is
• Physical tests for water

  1. Melting point = 0 oC

  2. Boiling point = 100 oC
• Purer water


  • Melts at exactly 0⁰C and boils at exactly 100⁰C
• Element


  Substance containing only one type of atom
• Metal


  • High MP/BP
  • Electrical conductors
  • Malleable
  • Shiny
  • Form alkaline oxides
• Non-metal


  • Low MP/BP
  • Electrical insulators
  • Brittle
  • Dull
  • Form acidic oxides
• The periodic table contains a staircase line between B and Al that separates metals and non-metals
• Element combustion


  Element + Oxygen → Element oxide
• Magnesium combustion


  2Mg(s) + O2(g) → 2MgO(s)
• Magnesium combustion


  • Bright white light and white powder formed
• Sulphur combustion


  S(s) + O2(g) → SO2(g)
• Sulphur combustion


  • Blue flame
• Hydrogen combustion


  2H2(g) + O2(g) → 2H2O(l)
• Hydrogen combustion


  • Squeaky pop!
• Metal oxide dissolving in water


  Forms alkaline solution
• Non-metal dioxide dissolving in water

  Forms acidic solution
• Determining if element is metal or non-metal

  1. Combust it in oxygen

  2. Dissolve the oxide formed

  3. Check the pH of the solution with an indicator
• Compound


  Substance containing more than one type of atom, chemically bonded together
• Compounds are often formed by heating their elements together
• Making compounds


  Heat elements together
• Making compounds


  • Heating zinc and sulphur forms zinc sulphide
• The properties of a compound are usually totally different from the properties of the elements the compound is made from
• Sodium chloride


  • Sodium (corrosive metal)
  • Chlorine (toxic gas)
  • Sodium chloride (common salt!)
• Types of compound


  • Ionic
  • Covalent
  • Metallic
• The bonding in a compound depends on whether the elements are metals or non-metals