period 3

• 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 has higher melting point than sodium oxide due to higher charge density of Mg2+ ions
  • Aluminium oxide has 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 forming a macromolecular covalent structure like diamond
  • Phosphorus and sulfur oxides have simple molecular structures held by weak intermolecular forces, so lower melting points
• Ionic oxides


  Contain O2- ions that accept protons from water to form alkaline solutions
• Sodium hydroxide formed from sodium oxide and water is a strong base that readily dissolves, giving a high pH
• Ionic oxides


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

  1. Form hydroxides

  2. Sodium hydroxide is a strong base, highly soluble

  3. Magnesium hydroxide is a weak base, not very soluble
• Simple covalent oxides


  Formed from non-metals like phosphorus and sulfur, form acidic solutions when dissolved in water
• Simple covalent oxides reacting with water

  1. Form acids

  2. Phosphoric acid

  3. Sulfurous acid
• Sulfuric acid is made from sulfur trioxide reacting with water
• 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 reacting with a base


  Forms a salt, no water produced
• Aluminium oxide reacting with an acid


  Forms a salt and water
• Sulfur oxides form two main products: sulfur dioxide and sulfur trioxide
• Need to know the bonding and structure of period 3 element oxides to explain their properties