Group 7

• This is a video for revision purposes on the topic of group 7 halogens for the AQA specification
• Halogens


  Group 7 nonmetal elements on the right side of the periodic table
• Halogens


  • Electron configuration 1s^2 2s^2 2p^5
  • Fluorine is a pale green gas, chlorine is a pale green gas, bromine is a reddish-brown liquid, iodine is a grey solid
• As we go down group 7


  The boiling point of the halogens increases
• As we go down group 7

  The electronegativity of the halogens decreases
• Halogen displacement reactions


  1. More reactive halogen displaces less reactive halide ion

  2. Electron is gained, forming new halide ion and less reactive halogen
• Bleach


  Sodium hypochlorite solution, formed by the disproportionation reaction of chlorine and sodium hydroxide
• Disproportionation reaction to form bleach

  Cl2 + 2 NaOH → NaCl + NaClO + H2O
• Uses of bleach


  • Water sterilization, paper/fabric bleaching, cleaning
• Water sterilization with chlorine

  1. Cl2 + H2O → H+ + Cl- + HClO (hypochlorous acid)

  2. HClO kills bacteria
• Sunlight decomposing chlorinated water

  • 4 Cl2 + 2 H2O → 4 H+ + 4 Cl- + O2
  • Reduces active chlorine (HClO) for water sterilization
• Advantages of chlorinating drinking water

  • Destroys microorganisms, long-lasting, reduces algae growth
• Disadvantages of chlorinating drinking water

  • Chlorine is toxic, can irritate respiratory system, potential to form carcinogenic byproducts
• Halide ions


  Ions of the halogen elements, have an extra electron compared to neutral halogens
• As we go down group 7

  Halide ion size increases, making them better reducing agents
• Halide ion reactions with concentrated sulfuric acid

  1. Cl- → Cl2 (gas)

  2. Br- → Br2 (gas)

  3. I- → I2 (solid)
• The oxidation state of sulfur changes in these reactions
• Reduction products of sulfuric acid

  • Sodium hydrogen sulfate
  • Sulfur dioxide
  • Sulfur
  • Hydrogen sulfide
• Oxidation states of sulfur

  • +6
  • +4
  • 0
  • -2
• Reaction of chloride ion with concentrated sulfuric acid

  Sodium hydrogen sulfate formation
• Reaction of bromide ion with concentrated sulfuric acid

  1. Bromine oxidation

  2. Sulfur dioxide formation
• Reaction of iodide ion with concentrated sulfuric acid

  1. Iodine oxidation

  2. Sulfur formation

  3. Hydrogen sulfide formation
• Sodium hydrogen sulfate is not a redox reaction, just a standard chemical reaction between a salt and an acid
• Bromide and iodide can further reduce sulfur in sulfuric acid
• Balancing half-equations


  • Crucial for understanding redox reactions
• Testing for halide ions with silver nitrate


  1. Add dilute nitric acid first

  2. White precipitate for chloride

  3. Cream precipitate for bromide

  4. Yellow precipitate for iodide
• Further testing with ammonia

  1. Chloride precipitate dissolves in dilute ammonia

  2. Bromide precipitate dissolves in concentrated ammonia

  3. Iodide precipitate insoluble in concentrated ammonia
• Flame tests for group 2 ions

  • Calcium - dark red
  • Strontium - red
  • Barium - green
• Testing for ammonium compounds

  Add sodium hydroxide, heat, observe ammonia gas production (turns red litmus blue)
• Testing for hydroxides


  Add to litmus paper, turns red litmus blue
• Testing for carbonates


  1. Add hydrochloric acid, observe carbon dioxide gas

  2. Bubble gas through limewater, turns cloudy
• Testing for sulfates


  Add hydrochloric acid, then barium chloride, white precipitate of barium sulfate forms
• Test for carbonates first, then sulfates, then halides to avoid false positives