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 produce 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)
• Sodium and magnesium oxides

  React quickly with air to form the oxides
• Aluminium oxide


  Reacts slowly with air, but faster if powdered due to increased surface area
• Phosphorus


  Spontaneously combusts in air
• Sulfur dioxide


  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 Mg2+ ions having greater charge density
• Aluminium oxide


  • Has slightly lower melting point than magnesium oxide due to some covalent character from Al3+ distorting electron cloud
• Silicon dioxide


  • Has higher melting point than other non-metal oxides due to forming a macromolecular covalent structure
• Phosphorus pentoxide and 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
• Reaction of sodium oxide with water

  Sodium oxide + water → Sodium hydroxide (alkaline solution)
• Sodium hydroxide


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


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


  Formed from non-metals like phosphorus and sulfur, form acidic solutions when dissolved in water (pH 0-2)
• Formation of phosphoric acid from phosphorus pentoxide

  Phosphorus pentoxide + 6 water → 4 phosphoric acid
• Formation of sulfurous acid from sulfur dioxide

  Sulfur dioxide + water → Sulfurous acid
• Formation of sulfuric acid from sulfur trioxide


  Sulfur trioxide + water → Sulfuric acid
• Sulfur forms two main oxide products: sulfur dioxide and sulfur trioxide
• Silicon dioxide


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


  Amphoteric, can act as both an acid and a base
• Reaction of aluminium oxide with a base

  Aluminium oxide + Sodium hydroxide → Sodium aluminate (salt)
• Reaction of aluminium oxide with an acid

  Aluminium oxide + Sulfuric acid → Aluminium sulfate + Water
• Acid-base reactions follow the general equation: Acid + Base → Salt + Water
• Sulfur oxides are an exception, as sulfur forms two main oxide products (SO2 and SO3)