Group 7

Group 7

Physical properties- Darker and denser as you go down
1. Fluorine = pale yellow gas
2. Chlorine = greenish gas
3. Bromine = red-brown liquid
4. Iodine= black solid
Size of atoms
1. Bigger down the group as each element has an extra shell filled.
Electronegativity
1. Decreases down the group
  1. Because more shells so more shielding from positive nucleus so less likely to attract electron density
Melting & boiling points
1. Increase down a group
  1. Because the larger the atoms the more electrons, meaning the van der Waals forces between molecules are stronger and require more energy to break
Chemical reactions
1. The oxidising ability of the halogens decreases down the group
  1. Halogens react by gaining electrons to become negative ions.
    1. They are oxidising agents and they themselves are reduced.
      1. e.g Cl(2) + 2e- -------> 2Cl-
2. Displacement reactions
  1. Halogens react with metal halides in a solution so that the halide in the compound is displaced by a more reactive halogen
    1. 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
Halide ions
1. Are the group 7 ions. They can act as reducing agents as they can give away electrons
  1. 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)
  2. So...reducing power increases down the group
2. All sodium halides react with sulphuric acid.....
  1. Sodium chloride
    1. NaCl + H(2)SO(4) ------> NaHSO(4) + HCl -Steamy fumes of hydrocholoric acid (HX)
  2. Sodium Bromide
    1. NaBr + H(2) SO(4) -----> NaHSO(4) + HBr -Steamy fumes of hydrogen Bromide (HX)
      1. 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!
  3. Sodium Iodide
    1. NaI + H(2)SO(4) -----> NaHSO(4) + HI - White stemy fumes of Hydrogen Iodide (HX)
      1. 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.
3. Test for iodides
  1. SN DA CA
    1. 1. Add SN
      1. Silver fluoride- no precipitate
      2. Silver chloride -white precipitate
        2. Add DA
        Disolves
      3. Silver Bromide- cream precipitate
        2. Add DA
        3. Add CA
        Dissolves
      4. Silver iodide- pale yellow precipitate
        2. Add DA
        3. Add CA
        Insoluable
  2. Silver nitrate... Dilute ammonia... Concentrated ammonia
Use of chlorine
1. -Poisonous gas - Soluble in water

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	Created by lucile over 9 years ago