Halogens

Halogens

1. Negative ions are called 'Halides'

2. Chlorine

   • chlorine water is colurless
     • displaces I- in KI
       • forms pink/violet solution with organic solvent (hexane)
         • Cl2 + I- ---> 2Cl- + I2
     • displaces Br- in KBr
       • forms orange/red solution with organic solvent (hexane)
         • Cl2 + 2Br- ---> 2Cl- + Br2
   • white precipitate in AgNO3
     • dissolves in dilute NH3
     • Ag+ + Cl- ---> AgCl
   • green gas at STP

3. Bromine

   • cream precipitate in AgNO3
     • Ag+ + Br- ---> AgBr
     • dissolves in conc NH3
   • red/brown liquid at STP
   • bromine water is orange
     • displaces I- in KI
       • forms pink/violet solution with organic solvent (hexane)
         • Br2 + I- ---> 2Br- + I2

4. Iodine

   • grey solid at STP
   • Iodine water is brown
     • displaces At-
       • I2 + 2A- ---> 2I- + At2
   • yellow precipitate in AgNO3
     • does not dissolve in NH3
     • Ag+ + I- ---> AgI

5. volatility decreases down the group

6. reactivity decreases down the group

7. Oxidising agents

   • become 'less oxidising' as they go down the group

8. boiling and melting point increase down the group

   • due to increasing strength of 'van der waals' forces as size and relative mass increases
     • outer electrons further away from positive nucleus are shielded more, due to more inner electrons
       • increase in difficulty of gaining extra electron to form ion (halide)

9. HNO3 before AgNO3

   • to clear up excess unwanted ions