Group 7 - Halogens

Group 7 - Halogens

1. Electronegativity

   • DECREASES down group
     • increasing nuclear distance and atomic radius
     • increasing shielding

2. Physical State

   • F2 and Cl2 are GASES
   • Br2 is LIQUID
   • I and At are SOLID
     • lattice structure

3. Boiling Point

   • INCREASES down group
     • larger atoms with more electrons
       • increased chance of induced dipoles and Van der Waal's forces

4. REDOX

   • Reducing Agents
     • HALIDES lose an electron easily
       • STRONGER down group
         • larger atoms, more shielding
     • reduce something else, being oxidised in the process
   • Oxidising Agents
     • HALOGENS gain an extra electron easily
       • WEAKER down group
         • increased atomic radius so less attraction to nucleus
     • oxidise something else, being reduced in the process

5. Reactions with H2SO4

   • NaX + H2S04 --> HX + NaHSO4
     • this is not a REDOX reaction since the S is not reduced at all
   • F- and Cl- are not strong reducing agents, so REDOX does not happen
     • NaF + H2SO4 --> NaHSO4
     • NaCl + H2SO4 --> NaHS04
   • Br- is a stronger reducing agent so the acid can be further reduced
     • NaBr + H2SO4 --> HBr + NaHSO4
       • 2HBr + H2SO4 --> SO2 + Br2 + 2H2O
         • oxidation state of S goes from +6 to +4
   • I- is a very strong reducing agent so the acid can be further reduce in a number of ways
     • NaI + H2SO4 -- > HI + NaHSO4
       • 2HI + H2SO4 --> SO2 + I2 + 2H20
         • S reduced from +6 to +4
       • 8HI + H2SO4 --> H2S + 4I2 + 4H2O
         • S reduced from +6 to -2
         • H2S is toxic and smells like rotten eggs
       • 6HI + H2SO4 --> S + 3I2 + 4H20
         • S reduced from +6 to 0

6. Reactions with AgNO3

   • F- doesn't form a precipitate
   • Cl- forms a white precipitate
     • dissolves in dilute ammonia
   • Br- forms a cream precipitate
     • dissolves in concentrated ammonia
   • I- forms a yellow precipitate
     • insoluble in ammonia
   • Ag+ + X- --> AgX
   • Add dilute nitric acid to remove any interfering ions before adding a few drops of AgNO3