halogens

• Reactivity of halogens

  Using our knowledge of halogen reactivity, we can deduce that: chlorine displaces bromine from bromides and iodine from iodides, bromine displaces iodine from iodides but cannot displace chlorine from chlorides, iodine cannot displace chlorine from chlorides
• Reactions of the halogens

  There are two key sets of reactions that we need to know:

  • reactions with metals to form salts
  • displacement reactions
• Displacement reactions


  Halogens can react with metal halides in solution. A halide is a compound containing a group 7 element and one other element, usually hydrogen or a metal. The reaction mixture changes colour during these displacement reactions, which is our way of knowing a reaction has taken place.
• Why is chlorine more reactive than bromine? Why is bromine more reactive than iodine?

  All the halogens have 7 electrons in their outer shell and therefore want to gain an electron to complete the shell, forming a 1- ion in the process. The easier it can gain that electron the more reactive it is. The smaller the distance between the positive nucleus and the outer shell, the more easily an electron is attracted, hence chlorine is more reactive than bromine and iodine
• Reactivity of halogens

  1. Chlorine displaces bromine from bromides and iodine from iodides

  2. Bromine displaces iodine from iodides but cannot displace chlorine from chlorides

  3. Iodine cannot displace chlorine from chlorides, nor bromine from bromides
• halogens exist as diatomic molecules
• as you go down group 7, the melting and boiling points increase
• at room temp:

  chlorine is a poisonous green gas, bromine is a red-brown liquid, iodine is grey crystalline solid
• displacement reactions between chlorine, bromine, iodine and potassium

  A) no reaction

  B) orange solution

  C) brown solution

  D) no reaction

  E) no reaction

  
• the halogens get less reactive as you go down the group, while the melting and boiling points increase as you go down (because they have stronger covalent bonds as you go down the group).