The Halogens

The Halogens

1. group seven:

2. TRENDS: as you go down group 7, the halogens...

   • become LESS reactive
     • this can be shown by looking at different reactions...
       • reactions with ALKALI METALS
         • eg. lithium, sodium, potassium, etc.
         • form SALTS qui s'appelle METAL HALIDES, eg...
           • sodium chloride - NaCl
           • potassium bromide - KBr
           • lithium iodide - LiI
         • become less vigorous as you go down the group
       • reactions with IRON
         • form COLOURED SOLIDS qui s'appelle IRON HALIDES, eg...
           • iron chloride - FeCl
           • iron bromide - FeBr
       • DISPLACEMENT REACTIONS
         • when a more reactive element ousts (displaces) a less reactive element from a compound
         • can be used to establish the REACTIVITY SERIES of the halogens...
           • ...you can work out which element is more reactive by seeing which displaces the other
     • because the outer electrons are further from the nucleus, so additional electrons are attracted less strongly
   • have HIGHER melting and boiling points (see above)

3. PROPERTIES

   • the halogens all...
     • are non-metals
     • have seven electrons in their outer shell
     • have coloured vapours
     • form diatomic molecules - pairs of atoms
       • ie Cl^2, Br^2
   • fluorine
     • very reactive
     • gas
     • poisonous
     • yellow
   • at room temperature
   • chlorine
     • fairly reactive
     • poisonous
     • dense
     • green
     • gas
   • bromine
     • orange
     • volatile liquid or gas
     • dense
     • poisonous
   • iodine
     • crystalline solid
       • dark grey
     • or vapour
       • purple

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