Lecture Notes: Group 17 (7) Elements - Halogens

Introduction

• Group 17, also known as Group 7 (halogens), covered in CIE specifications.
• Focus on trends and reactions.
• Available resources: A-level videos, PowerPoint slides for revision.

Overview of Halogens

• Elements:
  • Fluorine (F) - Pale yellow gas
  • Chlorine (Cl) - Green gas
  • Bromine (Br) - Brownish-orange liquid
  • Iodine (I) - Grey solid
• Trends:
  • Boiling points increase down the group due to stronger Van der Waals forces.
  • Physical state transitions from gas to solid down the group.
  • Electronegativity decreases down the group; fluorine is the most electronegative.

Hydrogen Halides

• Properties:
  • Acidic gases, dissolve in water to form acids.
  • Examples: HCl (hydrochloric acid), HBr (hydrobromic acid), HI (hydroiodic acid).
  • Form white misty fumes, dissociate in water.
• Reactions:
  • Stability decreases down the group when heated.
  • Hydrogen halides react with ammonia to form ammonium halides.

Halide Ions and Silver Nitrate Test

• Procedure:
  • Add dilute nitric acid, then silver nitrate to test for halide ions.
  • Precipitate colors: White (Cl⁻), Cream (Br⁻), Yellow (I⁻).
• Ammonia Test:
  • Chloride: Dissolves in dilute ammonia.
  • Bromide: Dissolves in concentrated ammonia.
  • Iodide: Insoluble in both.

Displacement Reactions

• Concept: More reactive halogens displace less reactive halides.
• Reactivity decreases down the group.
• Examples:
  • Chlorine can displace bromide and iodide ions.
  • Bromine can displace iodide ions.

Oxidation States of Halogens

• Variety of Oxidation States:
  • Common states: -1, 0, +1, +3, +5, +7.
• Disproportionation Reactions:
  • Halogens undergo self-oxidation and reduction in reactions with alkalis.

Halogen Reactions with Alkalis

• Cold Alkalis: Form sodium halides and hypohalites, e.g., NaOBr.
• Hot Alkalis: Form sodium chlorate and other higher oxidation state compounds.

Halide Ions as Reducing Agents

• Halide ions lose electrons, act as reducing agents.
• Reactivity as reducing agents increases down the group.
• Reactions with Sulfuric Acid:
  • Chlorides: No reduction.
  • Bromides: Produce HBr and SO₂.
  • Iodides: Produce HI, SO₂, S, and toxic H₂S.

Bleach Production

• Reaction: Chlorine with sodium hydroxide forms bleach (sodium chlorate(I)).
• Uses: Water treatment, bleaching fabrics, cleaning agents.

Water Sterilization

• Chlorine in water produces chlorate ions, sterilizes by killing bacteria.
• Common in drinking water and swimming pools.

PVC (Polyvinyl Chloride)

• Properties: Tough, resistant to electricity, used in home applications.
• Uses: Electrical coverings, window frames, piping, resistant to heat.

Conclusion

• Group 17 elements are versatile with significant practical applications.
• Resources available for further study and revision.

• Reminder: PowerPoint slides available for detailed study aid.