The Halogens (Group 7)

• What consists of the halogens?

  • Fluorine
  • Chlorine
  • Bromine
  • Iodine
  • Astatine
• What is the physical appearance of fluorine?


  Pale, yellow gas
• What is the physical appearance of chlorine?


  Green gas
• What is the physical appearance of bromine?

  Orange - brown liquid
• What is the physical appearance of iodine?

  Grey / blue solid
• What do halogen all exist as?

  Diatomic molecules X2
• What type of molecules are halogens?

  Simple covalent
• Explain the trend in boiling point in halogens

  • The boiling point increases as you go down the group
  • More electrons
  • This means stronger London forces
  • Therefore more energy is needed to break the intermolecular forces
• Are halogens an oxidising or reducing agent?


  Oxidising because they have oxidised other species
• What ions do halogens form?

  -1 ions as they gain 1 electron
• Describe and explain the reactivity trend in halogens as you go down the group


  • The reactivity decreases as you go down the group
  • This is because when they react they gain an electron
  • Atomic radius increases
  • More inner shells so shielding increases
  • The electrostatic attraction between nucleus and outer electron becomes weaker
  • Harder for larger halogens to to attract the electron needed to into the p sub-shell to form a halide ion
• As you go down group 7, do they become less powerful oxidising agents?And explain your reasoning.


  • Yes
  • Because it's harder to gain an electron due to increasing atomic radius and shielding
• What happens when a more reactive halogen displaces a less reactive halide ion in solution?


  A visible colour change occurs that allow the halogen product to be identified
• What colour does solution turn if bromide (Br-) is displaced?


  Orange
• What colour does solution turn if iodine (I-) is displaced?


  Orange / brown
• What colour does solution turn if no displacement occurs?

  Colourless
• What organic solvent is used clearly visualise the halogen products?

  Cyclohexane
• What colour does organic layer turn if bromide (Br-) is displaced in cyclohexane?


  Orange
• What colour does organic layer turn if iodide (I-) is displaced in cyclohexane?


  Purple
• What is disproportionation?


  A redox reaction in which the same element is both oxidised and reduced
• What 2 reactions of chlorine are disproportionation reactions?


  • Chlorine with water
  • Chlorine with cold, dilute aqueous sodium hydroxide
• What is equation for chlorine reacting with water?

  Cl2 (aq) + H2O (L) -> HClO (aq) + HCl (aq)
• What is oxidised and reduced in Cl2 + H2O -> HClO + HCl?

  • Oxidised = Chlorine in chloric(I) acid (0 -> +1)
  • Reduced = Chlorine in hydrochloric acid (0 -> -1)
• What is the use of chlorine with water?


  Disinfects drinking water
• What are benefits of using chlorine for water disinfection?


  • Kills bacteria
  • Prevents reinfection further down the supply
  • Removes bad taste, smell and discolouration
• What are the risks of using chlorine for water disinfection?

  • Chlorine gas causes severe irritation if inhaled
  • Reacts with organics to form carcinogenic chlorinated hydrocarbons
  • They're toxic / poisonous
• What is another word for chlorine in cold, dilute aqueous sodium hydroxide?

  Bleach
• What is the equation for chlorine in cold, dilute aqueous sodium hydroxide?

  Cl2 + 2NaOH -> NaCl + NaClO + H2O
• What is oxidised and reduced in Cl2 + 2NaOH -> NaCl + NaClO + H2O?

  • Oxidised = chlorine in sodium chlorate (0 -> +1)
  • Reduced = chlorine in sodium chloride (0 -> -1)
• How does bleach kill bacteria?

  The chlorate(I) ions that act as oxidising agents
• Why are halogens non-polar?


  • Because they have the same electronegativity so no permanent dipole is created
  • Only intermolecular forces possible are london forces