Halogens

• What are the trends in boiling Points of halogens?

  exist as diatomic molecules, down a group= more electrons more London forces and more energy required = higher boiling point
• what are the most common reactions of halogens?

  redox reactions as they gain one electron and are therefore reduced, the other species is therefore oxidised so halogens are oxidising agents
• How can a halogen halide displacement reaction be carried out?

  Add each halogen to aqueous solutions of the other halide, if more reactive the halogen will displace and the colour of solution will change - this can help show that reactivity decreases down the group
• how to tell iodine and bromine apart?

  both are similar orange colour, therefore add non polar organic solvent eg.cyclohexane = iodine will form purple laye
• What is the order reactivity of the halogens?

  Chlorine- reacts with both bromine= orange and iodine= purple

  bromine- reacts with iodine= purple

  iodine - doesn’t react with any halides
• What is the reactivity of astatine?

  Least reactive halogen but is just a prediction as it rapidly decays and has not been seen yet
• what is the trend in reactivity of reactivity down group 7?

  decreases, as atomic radius increases= more shielding and less attraction, therefore harder to gain a singular electron
• what is disproportination?

  a redox reaction where the same element is both oxidised and reduced

  eg chlorine + water

  chlorine + sodium hydroxide
• why is chlorine used in water?

  • water purification- by killing harmful bacteria
  • one chlorine atom is reduced and the other is oxidised
  • chloric acid and ClO- ions are formed= kill bacteria
  • chloric acids is also weak bleach= turns indicator red then colourless

  
• How does chlorine react with cold dilute aqueous sodium hydroxide?

  • if water contains dissolved sodium hydroxide much more chlorine dissolves
  • forms a large concentration of chlorate ions in sodium chlorate

  
• what are the benefits and risks of chlorine use in water?

  Benefits: kills bacteria, reduces risks of cholera adn typhoid Risks: is a respiratory irritant and in large concs can be fatal

  chlorine can react with hydrocarbons such as methane released by decaying vegetations = chlorinated hydrocarbons