Halogens

• What is the general trend in reactivity for halogens?

  Decreases going down the group
• Why does the boiling points increase going down the group?

  There are more electrons

  Stronger London forces (induced dipole-dipole)

  More energy required to break the intermolecular forces
• Why does reactivity decrease going down group 7?

  Atomic radius increases

  More inner shells so shielding increases

  Less nuclear attraction to capture an electron from another species
• What is the colour of Cl2 in water?

  pale green
• What is the colour of Cl2 in cyclohexane?

  Pale green
• What is the colour of Br2 in water?

  orange
• What is the colour of Br2 in cyclohexane?

  orange
• What is the colour of I2 in water?

  Brown
• What is the colour of I2 in cyclohexane?

  Violet
• What is the rule for halogen - halide displacement reactions?


  The halogen can only displace the halide ion when the halogen is MORE recative than the halide ion.
• What is the reaction called when the same element is both oxidised and reduced?

  Disproportionation
• State the disproportionation reaction of Cl2?

  Cl2(aq) + H2O(l) —> HClO(aq) + HCl(aq)
• What are the risks of chlorine use?

  Toxic and respiratory irritant
• What is the benefit of chlorine use?

  Having safe water to drink