Group 7 - Halogens

Anexos:

• Applications of Chlorine

1. Electronegativity
   1. DECREASES down group
      1. increasing nuclear distance and atomic radius
      2. increasing shielding
2. Physical State
   1. F2 and Cl2 are GASES
   2. Br2 is LIQUID
   3. I and At are SOLID
      1. lattice structure
3. Boiling Point
   1. INCREASES down group
      1. larger atoms with more electrons
         1. increased chance of induced dipoles and Van der Waal's forces
4. REDOX
   1. Reducing Agents
      1. HALIDES lose an electron easily
         1. STRONGER down group
            1. larger atoms, more shielding
      2. reduce something else, being oxidised in the process
   2. Oxidising Agents
      1. HALOGENS gain an extra electron easily
         1. WEAKER down group
            1. increased atomic radius so less attraction to nucleus
      2. oxidise something else, being reduced in the process
5. Reactions with H2SO4
   1. NaX + H2S04 --> HX + NaHSO4
      1. this is not a REDOX reaction since the S is not reduced at all
   2. F- and Cl- are not strong reducing agents, so REDOX does not happen
      1. NaF + H2SO4 --> NaHSO4
      2. NaCl + H2SO4 --> NaHS04
   3. Br- is a stronger reducing agent so the acid can be further reduced
      1. NaBr + H2SO4 --> HBr + NaHSO4
         1. 2HBr + H2SO4 --> SO2 + Br2 + 2H2O
            1. oxidation state of S goes from +6 to +4
   4. I- is a very strong reducing agent so the acid can be further reduce in a number of ways
      1. NaI + H2SO4 -- > HI + NaHSO4
         1. 2HI + H2SO4 --> SO2 + I2 + 2H20
            1. S reduced from +6 to +4
         2. 8HI + H2SO4 --> H2S + 4I2 + 4H2O
            1. S reduced from +6 to -2
            2. H2S is toxic and smells like rotten eggs
         3. 6HI + H2SO4 --> S + 3I2 + 4H20
            1. S reduced from +6 to 0
6. Reactions with AgNO3
   1. F- doesn't form a precipitate
   2. Cl- forms a white precipitate
      1. dissolves in dilute ammonia
   3. Br- forms a cream precipitate
      1. dissolves in concentrated ammonia
   4. I- forms a yellow precipitate
      1. insoluble in ammonia
   5. Ag+ + X- --> AgX
   6. Add dilute nitric acid to remove any interfering ions before adding a few drops of AgNO3