Lecture Notes: Period 3 Elements in A-level Chemistry

Overview

• Focus on Period 3 elements and their reactions
• Emphasis on how they interact with other substances

Elements in Period 3

• Elements: Sodium (Na), Magnesium (Mg), Aluminium (Al), Silicon (Si), Phosphorus (P), Sulfur (S), Chlorine (Cl), Argon (Ar)
• Shells: Same number of shells across period, varying outer shell electrons
• Types:
  • Metals: Sodium, Magnesium, Aluminium
  • Non-metals: Silicon, Phosphorus, Sulfur, Chlorine, Argon

Electronic Configuration and Bonding

• Sodium & Magnesium: S block elements, end with s shell
• Rest of Period 3: P block elements, p shell filling
• Bonding Types:
  • Metals (Na, Mg, Al): Metallic bonding
  • Silicon: Giant covalent structures
  • Phosphorus, Sulfur, Chlorine: Simple covalent structures
  • Argon: Monoatomic

Properties and Forces

• Melting & Boiling Points:
  • High in metallic and giant covalent structures
  • Low in simple covalent and monoatomic structures
• Forces:
  • Metallic bonding > Van der Waals forces

Atomic Radius and Ionization Energy

• Atomic Radius: Decreases across the period
  • Due to increased nuclear charge
• Ionization Energy:
  • Reflects difficulty in removing outermost electron
  • Drops between groups 2 & 3, 5 & 6 due to electron pairing

Reactions with Water

• Sodium Reaction:
  • Produces sodium hydroxide and hydrogen gas
  • Highly exothermic, pH 13-14
• Magnesium Reaction:
  • Produces magnesium hydroxide and hydrogen gas
  • Slow with cold water, faster with steam, pH 10

Reactions with Oxygen

• Sodium to Sulfur:
  • Sodium: Sodium oxide (ionic)
  • Magnesium: Magnesium oxide (ionic)
  • Aluminium: Needs to be rubbed, forms aluminium oxide (ionic with covalent characteristics)
  • Silicon: Silicon dioxide (giant covalent)
  • Phosphorus: P4O10 or P2O3 (limited O2)
  • Sulfur: SO2 and SO3 (covalent)

Oxides Reactions with Water

• Sodium Oxide:
  • Forms strongly alkaline sodium hydroxide, pH 13-14
• Magnesium Oxide:
  • Forms magnesium hydroxide, pH 10
• Aluminium & Silicon Oxides: Insoluble in water
• Phosphorus Oxides: Forms phosphoric acid, strong acid, pH 1-2
• Sulfur Oxides:
  • SO2 forms sulfurous acid, weak acid, pH 2-3
  • SO3 forms sulfuric acid, strong acid, pH 0-1

Acid-Base Reactions

• Basic Oxides: React with acids to produce salt and water
• Amphoteric Oxides (Aluminium Oxide):
  • Acts as both acid and base
• Acidic Oxides:
  • React with strong bases
• Environmental Impact:
  • Sulfur dioxide contributes to acid rain

Structural Notes

• Phosphoric Acid: P bonded to O, with H
• Sulfurous/Sulfuric Acid: S double bonded to O, forms acidic ions when hydrogen is removed

Environmental Relevance

• Emphasis on pollution and removal of gases from industrial waste

Additional Notes

• Acid strength is distinct from concentration
• Applications in practical observations and experiments in school settings