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• This video is dedicated to AQA chemistry and covers the properties of period 3 elements and their oxides
• Sodium is more reactive than magnesium as the amount of energy required to remove an electron from sodium is lower than to remove two electrons from magnesium
• Sodium reacting with cold water

  1. Forms a ball

  2. Fizzes

  3. Produces hydrogen gas

  4. Produces an alkaline solution of sodium hydroxide
• Magnesium reacting with water

  1. Forms a weak alkaline solution of magnesium hydroxide

  2. Reacts much faster with steam to form magnesium oxide and hydrogen
• Period 3 elements react with oxygen to form oxides, except sulfur which can form sulfur dioxide (oxidation number +4) or sulfur trioxide (oxidation number +6)
• Oxides formed by period 3 elements

  • Sodium oxide
  • Magnesium oxide
  • Aluminium oxide
  • Silicon dioxide
  • Phosphorus pentoxide
  • Sulfur dioxide
• Sodium/magnesium reacting with air

  Forms their respective oxides quickly
• Aluminium oxide reacting with air

  Reacts slowly, but faster if powdered
• Phosphorus reacting with air

  Spontaneously combusts
• Sulfur dioxide reacting with air

  Burns steadily in oxygen
• Group 3 metal oxides

  • Form giant ionic lattices, have high melting points due to strong electrostatic forces
• Magnesium oxide


  • Higher melting point than sodium oxide due to higher charge density of Mg2+ ions
• Aluminium oxide


  • Slightly lower melting point than magnesium oxide due to some covalent character from distortion of electron cloud
• Silicon dioxide


  • Has higher melting point than other non-metal oxides due to its macromolecular covalent structure
• Phosphorus pentoxide, sulfur dioxide

  • Have lower melting points as they form simple molecular structures held by weak intermolecular forces
• Ionic oxides


  Contain O2- ions that accept protons from water to form alkaline solutions
• Sodium hydroxide


  A strong base that readily dissolves in water, giving a high pH
• Ionic oxides


  Contain the O2- ion that accepts protons from water molecules when dissolved in solution, forming hydroxides
• Ionic oxide + water

  1. Forms hydroxide

  2. Releases H+
• Sodium hydroxide

  Strong base that readily dissolves in solution, resulting in high pH (12-14)
• Magnesium hydroxide


  Weak base that does not dissolve well in water, resulting in moderate pH (9-10)
• Ionic oxides form basic solutions
• Simple covalent oxides


  Formed from non-metals like phosphorus and sulfur, form acidic solutions (pH 0-2)
• Phosphorus pentoxide + water

  1. Forms phosphoric acid

  2. Dissociates into 3 H+ and PO4 2-
• Sulfur dioxide + water

  1. Forms sulfurous acid

  2. Dissociates into 2 H+ and SO3 2-
• Sulfur trioxide + water

  1. Forms sulfuric acid

  2. Dissociates into 2 H+ and SO4 2-
• Sulfur forms two main oxide products: SO2 and SO3
• Silicon dioxide


  Insoluble in water, reacts with bases to form salts
• Aluminium oxide


  Amphoteric, can act as both an acid and a base
• Aluminium oxide + base

  Forms aluminium salt, no water produced
• Aluminium oxide + acid

  Forms aluminium salt + water
• Acid + base → salt + water (general reaction)
• Sulfur oxides are an exception, forming two different products (SO2 and SO3)