Group 7

• group 7 = halogens
• fluorine = yellow gas

  chloring = green gas

  bromine = brown liquid

  iodine = black / grey solid
• boiling points increase as you go down group 7 due to :

  • increasing size of atom
  • increasing mr
  • so increasing vdw forces
• top of group 7 = gasses

  bottom = solid
• electronegativity decreases down group 7:

  • atomic radius increases so distance between nucleas and outer electrons increases
  • shielding increases
• more reactive halogens displace less reactive halide ions
• reactivity for halogens:

  • decreases as you go down the group
  • for reaction to occur electron needs to be gained , easier to gain electrons with smaller atoms
• addition of chlorine water to :

  • KCL- no reaction
  • KBR- br2 made (orange solution)
  • KI- I2 made (brown solution)
• addition of bromine to:

  • KCL- no reaction
  • KBR- no reaction
  • KI- I2 made (brown solution)
• addition of iodine to:

  • KCL- no reaction
  • KBR- no reaction
  • KI- no reaction
• ionic radius increases as you go down the group

  distance between nucleus and outer electron increases

  attractive force gets weaker

  outer electron lost more easily , so I- is a more powerful reducing agent than f-
• halide ions are reducing agents
• observations for chloride when reacted with sulfuric acid:

  produces nahso4 + hcl

  white misty fumes produced
• for bromide ions sulfuric acid forms nahso4 and so2
• for iodide ions the sulfuric acid forms nahso4 and so2 and s and h2s
• test for halides using silver nitrates;

  • add dilute nitric acid HNO3
  • then add silver nitrate solution AGNO3
  • chlorine = white precipitate , bromine = cream precipitate , iodine = yellow precipitate
  • then add ammonia nh3
  • white precipitate dissolves in dilute nh3 , cream precipitate in concentrated nh3 and yellow insolube
• testing for ammonium:

  • add naoh
  • gently heat
  • then hold damp red litmus paper at mouth of tube and it should turn blue
• test for carbonates:

  hcl reacts with carbonated to produce co2

  when bubbled through limewater it turns cloudy
• overall trends for group 7:

  • reactivity decreases
  • electronegativity decreases
  • boiling point increase
• give one reason why water is treated with chlorine

  to kill bacteria - however only used in small amounts - as is toxic
• bleach:

  • made via a disproportionation reaction
  • 2NAOH + CL2 = NACLO + NACL + H20
  • used as cleaning agent and to treat water
• acid base reactions for halide ions with sulfuric acid:

  $Nacl +$$H2so4 =$$Nahso4 +$$Hcl$

  $NaBr+$$H2so4 =$$Nahso4 +$$Hbr$

  $NaI +$$h2so4 =$$Nahso4 +$$HI$
• observations for reaction of bromide ions with sulfuric acid:

  bromide converted into bromine

  produces so2

  half equations:

  • $2Br- =$$Br2 +$$2E -$
  • H2SO4 + 2H+ + 2E- = SO2 + 2H20
  • orange vapour of br2 produced
• observation for reaction of iodide ions with sulfuric acid:

  iodide is converted into iodine

  produces S - yellow solid

  produces h2s - rotten egg smell
• flame tests:

  dark red = calcium

  red = strontium

  green = barium
• explain why electronegativity of halogens increases down the group

  as you go down the group shielding increases

  theres a weaker attraction between nucleus and shared pair of electrons
• what is the role of h2so4 in acid base reactions

  proton doner
• explain why complexes formed from transition metal ions are coloured

  1. absorb some wavelegnths of visible light
  2. to excite electrons in d orbital
  3. complementary wavelegnths then reflected
• what is the role of sulfuric acid in redox reactions with halide ions


  sulfuric acid is the oxidising agent