Group 7

Group 7

1. Physical properties- Darker and denser as you go down

   • Fluorine = pale yellow gas
   • Chlorine = greenish gas
   • Bromine = red-brown liquid
   • Iodine= black solid

2. Size of atoms

   • Bigger down the group as each element has an extra shell filled.

3. Electronegativity

   • Decreases down the group
     • Because more shells so more shielding from positive nucleus so less likely to attract electron density

4. Melting & boiling points

   • Increase down a group
     • Because the larger the atoms the more electrons, meaning the van der Waals forces between molecules are stronger and require more energy to break

5. Chemical reactions

   • The oxidising ability of the halogens decreases down the group
     • Halogens react by gaining electrons to become negative ions.
       • They are oxidising agents and they themselves are reduced.
         • e.g Cl(2) + 2e- -------> 2Cl-
   • Displacement reactions
     • Halogens react with metal halides in a solution so that the halide in the compound is displaced by a more reactive halogen
       • They get less reactive as you go down the group e.g F(2) will displace all other halide solutions as it is the highest in group 7 where as I(2) will not displace any of the halide solutions as it is not very reactive

6. Halide ions

   • Are the group 7 ions. They can act as reducing agents as they can give away electrons
     • The larger the ion the more easily it loses the electron as it is being held less tightly from the positively charged nucleus (further away and more electron shielding)
     • So...reducing power increases down the group
   • All sodium halides react with sulphuric acid.....
     • Sodium chloride
       • NaCl + H(2)SO(4) ------> NaHSO(4) + HCl -Steamy fumes of hydrocholoric acid (HX)
     • Sodium Bromide
       • NaBr + H(2) SO(4) -----> NaHSO(4) + HBr -Steamy fumes of hydrogen Bromide (HX)
         • Redox reactions- Then the Hbr goes under a redox reaction because the sulphur in the suphuric acid is a strong enough oxidising agent to oxidise the bromide. 2H(+) + 2Br(-) + H(2)SO(4) -------> Br(2) + SO(2) + 2H(2)O
           • Br(2) produces brown fumes which is bricky colour, so match this with SO(2) as this is acid rain and the acid rain will erode the bricks!
     • Sodium Iodide
       • NaI + H(2)SO(4) -----> NaHSO(4) + HI - White stemy fumes of Hydrogen Iodide (HX)
         • Redox reaction- H(2)SO(4) + 8H(+) + 8I(-) -----> H(2)S + H(2)O +4I(2)
           • I(2) produces a puple gas which is like lavender coloured- so match this with H(2)S as that's a smelly egg smell so we need to cover up that stench with the lavender.
   • Test for iodides
     • SN DA CA
       • 1. Add SN
         • Silver fluoride- no precipitate
         • Silver chloride -white precipitate
           • 2. Add DA
             • Disolves
         • Silver Bromide- cream precipitate
           • 2. Add DA
             • 3. Add CA
               • Dissolves
         • Silver iodide- pale yellow precipitate
           • 2. Add DA
             • 3. Add CA
               • Insoluable
     • Silver nitrate... Dilute ammonia... Concentrated ammonia

7. Use of chlorine

   • -Poisonous gas - Soluble in water