The halogens

• What group elements are referred to as halogens?

  Group 7
• What are two properties of halogens?

  • Low melting and boiling points
  • Exist as diatomic molecules
• What is the trend in boiling point down group 7?

  Increases down the group
• Why does the boiling point increase down group 7?

  Atom size increases, stronger London forces
• What is the trend in reactivity down group 7?

  Reactivity decreases down the group
• Why does reactivity decrease down group 7?

  Atomic radius and electron shielding increase
• What is the trend in oxidising ability down group 7?

  Decreases down the group
• Why does oxidising ability decrease down group 7?

  Cl has fewest shells, strongest attraction
• What is the trend in reducing ability of the halides down the group?

  Increases down the group
• Why does reducing ability increase down the group?

  I- has most shells, weakest attraction
• What is the reaction called when a more reactive halogen displaces a less reactive halide?

  Displacement reaction
• What is the colour of chlorine in water?

  Pale green
• What is the colour of bromine in water?

  Orange
• What is the colour of iodine in water?

  Brown
• What is the colour of chlorine in cyclohexane?

  Pale green
• What is the colour of bromine in cyclohexane?

  Orange
• What is the colour of iodine in cyclohexane?

  Violet
• Which halides can be oxidised by chlorine?

  Br- & I- ions
• Write the equation for chlorine oxidising bromide ions.

  Cl₂ (aq) + 2Br- (aq) → 2Cl- (aq) + Br₂ (aq)
• Write the equation for Cl₂ oxidising 2I-.

  Cl₂ (aq) + 2I- (aq) → 2Cl- (aq) + I₂ (aq)
• Which halides can be oxidised by bromine?

  I- ions
• Write the equation for bromine oxidising iodide ions.

  Br₂ (aq) + 2I- (aq) → 2Br- (aq) + I₂ (aq)
• Which halides can be oxidised by iodine?

  Does not oxidise Cl- or Br-
• What is disproportionation?

  Oxidation and reduction of the same element
• What is the equation for the reaction of Cl₂ with water?

  Cl₂ (g) + H₂O (l) → HClO (aq) + HCl (aq)
• What type of reaction is the reaction of chlorine with water?

  Disproportionation; chlorine is both oxidised and reduced
• Why is chlorine added to drinking water?

  Kills bacteria, makes it safer to drink
• What are the two forms of the chlorate ion?

  • ClO- is chlorate (I)
  • ClO₃- is chlorate (V)
• What is the equation for forming bleach?

  Cl₂ (aq) + 2NaOH (aq) → NaCl (aq) + NaClO (aq) + H₂O (l)