1. KNOCKHARDY PUBLISHING
AN INTRODUCTION TO
GROUP VII
2008 SPECIFICATIONS
KNOCKHARDY PUBLISHING

2. KNOCKHARDY PUBLISHING
GROUP 7 (HALOGENS)
INTRODUCTION
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3. GROUP VII CONTENTS Trends in appearance
Trends in electronic configuration
Trends in in Atomic and Ionic radius
Trends in Electronegativity
Trends in oxidation power
Displacement reactions
Other reactions
Testing for halides – AgNO3
Testing for halides - concentrated H2SO4
Volumetric analysis of chlorate(I) in bleach

4. GROUP PROPERTIES • exist as separate diatomic molecules… eg Cl2
GENERAL • non-metals
• exist as separate diatomic molecules… eg Cl2
• all have the electronic configuration ... ns2 np5
TRENDS • appearance
• boiling point
• electronic configuration
• electronegativity
• atomic size
• oxidising power

5. GROUP TRENDS APPEARANCE BOILING POINT INCREASES down GroupF2
Cl2
Br2 I2
Colour
Yellow
Green
Red/brown
Grey
State (at RTP)
GAS
GAS
LIQUID
SOLID
BOILING POINT F2
Cl2
Br2 I2
Boiling point / °C
- 188
- 34 58
183
INCREASES down Group
• increased size makes the van der Waals forces increase
• more energy is required to separate the molecules

6. ELECTRONIC CONFIGURATION
GROUP TRENDS
ELECTRONIC CONFIGURATION F Cl Br I
Atomic Number 9 17 35 53
Old
2,7
2,8,7
2,8,18,7
2,8,18,18,7
New
… 2s2 2p5
…3s2 3p5
… 4s2 4p5
… 5s2 5p5
• electrons go into shells further from the nucleus

7. GROUP TRENDS ATOMIC & IONIC RADIUS ATOMIC RADIUS INCREASES down GroupF Cl Br I
Atomic radius / nm
0.064
0.099
0.111
0.128 F¯
Cl¯
Br¯ I¯
Ionic radius / nm
0.136
0.181
0.195
0.216
ATOMIC RADIUS INCREASES down Group
IONIC RADIUS INCREASES down Group
• the greater the atomic number the more electrons there are
these go into shells increasingly further from the nucleus
• ions are larger than atoms - the added electron repels the
others so radius gets larger

8.  attraction drops off as distance increases
GROUP TRENDS
ELECTRONEGATIVITY F Cl Br I
Electronegativity
4.0
3.5
2.8
2.5
DECREASES down Group
• the increasing nuclear charge due to the greater number of protons
should attract electrons more, but there is an ...
an increasing number of shells;
 more shielding and less pull on electrons
an increasing atomic radius
 attraction drops off as distance increases

9. GROUP TRENDS OXIDISING POWER • halogens are oxidising agents
• they need one electron to complete their octet
• the oxidising power gets weaker down the group

10. GROUP TRENDS OXIDISING POWER • halogens are oxidising agents
• they need one electron to complete their octet
• the oxidising power gets weaker down the group
• the trend can be explained by considering the nucleus’s attraction
for the incoming electron which is affected by the...
• increasing nuclear charge which should attract electrons more
but this is offset by • INCREASED SHIELDING
• INCREASING ATOMIC RADIUS

11. This is demonstrated by reacting the halogens with other halide ions.
GROUP TRENDS
OXIDISING POWER
• halogens are oxidising agents
• they need one electron to complete their octet
• the oxidising power gets weaker down the group
• the trend can be explained by considering the nucleus’s attraction
for the incoming electron which is affected by the...
• increasing nuclear charge which should attract electrons more
but this is offset by • INCREASED SHIELDING
• INCREASING ATOMIC RADIUS
This is demonstrated by reacting the halogens with other halide ions.

12. HALOGENS - DISPLACEMENT REACTIONS
THE DECREASE IN REACTIVITY DOWN THE GROUP IS DEMONSTRATED USING DISPLACEMENT REACTIONS...

13. HALOGENS - DISPLACEMENT REACTIONS
THE DECREASE IN REACTIVITY DOWN THE GROUP IS DEMONSTRATED USING DISPLACEMENT REACTIONS...
A SOLUTION OF THE HALOGEN IS ADDED TO A SOLUTION OF A HALIDE
HALIDES ARE SALTS FORMED FROM HALOGENS (see next slide for examples)
A MORE REACTIVE HALOGEN WILL DISPLACE A LESS REACTIVE ONE

14. HALOGENS - DISPLACEMENT REACTIONS
THE DECREASE IN REACTIVITY DOWN THE GROUP IS DEMONSTRATED USING DISPLACEMENT REACTIONS...
A SOLUTION OF THE HALOGEN IS ADDED TO A SOLUTION OF A HALIDE
HALIDES ARE SALTS FORMED FROM HALOGENS (see next slide for examples)
A MORE REACTIVE HALOGEN WILL DISPLACE A LESS REACTIVE ONE
e.g. CHLORINE + SODIUM BROMIDE BROMINE + SODIUM CHLORIDE

15. HALOGENS - DISPLACEMENT REACTIONS
THE DECREASE IN REACTIVITY DOWN THE GROUP IS DEMONSTRATED USING DISPLACEMENT REACTIONS...
A SOLUTION OF THE HALOGEN IS ADDED TO A SOLUTION OF A HALIDE
HALIDES ARE SALTS FORMED FROM HALOGENS (see next slide for examples)
A MORE REACTIVE HALOGEN WILL DISPLACE A LESS REACTIVE ONE
e.g. CHLORINE + SODIUM BROMIDE BROMINE + SODIUM CHLORIDE
Cl2(aq) NaBr(aq) ——> Br2(aq) NaCl(aq)

16. HALOGENS - DISPLACEMENT REACTIONS
THE DECREASE IN REACTIVITY DOWN THE GROUP IS DEMONSTRATED USING DISPLACEMENT REACTIONS...
A SOLUTION OF THE HALOGEN IS ADDED TO A SOLUTION OF A HALIDE
HALIDES ARE SALTS FORMED FROM HALOGENS (see next slide for examples)
A MORE REACTIVE HALOGEN WILL DISPLACE A LESS REACTIVE ONE
e.g. CHLORINE + SODIUM BROMIDE BROMINE + SODIUM CHLORIDE
Cl2(aq) NaBr(aq) ——> Br2(aq) NaCl(aq)
Cl2(aq) Br¯(aq) ——> Br2(aq) Cl¯(aq)

17. HALOGENS - DISPLACEMENT REACTIONS
THE DECREASE IN REACTIVITY DOWN THE GROUP IS DEMONSTRATED USING DISPLACEMENT REACTIONS...
A SOLUTION OF THE HALOGEN IS ADDED TO A SOLUTION OF A HALIDE
HALIDES ARE SALTS FORMED FROM HALOGENS (see next slide for examples)
A MORE REACTIVE HALOGEN WILL DISPLACE A LESS REACTIVE ONE
e.g. CHLORINE + SODIUM BROMIDE BROMINE + SODIUM CHLORIDE
CHLORINE + SODIUM IODIDE IODINE + SODIUM CHLORIDE

18. HALOGENS - DISPLACEMENT REACTIONS
THE DECREASE IN REACTIVITY DOWN THE GROUP IS DEMONSTRATED USING DISPLACEMENT REACTIONS...
A SOLUTION OF THE HALOGEN IS ADDED TO A SOLUTION OF A HALIDE
HALIDES ARE SALTS FORMED FROM HALOGENS (see next slide for examples)
A MORE REACTIVE HALOGEN WILL DISPLACE A LESS REACTIVE ONE
e.g. CHLORINE + SODIUM BROMIDE BROMINE + SODIUM CHLORIDE
CHLORINE + SODIUM IODIDE IODINE + SODIUM CHLORIDE
BROMINE + SODIUM IODIDE IODINE + SODIUM BROMIDE

19. HALOGENS - DISPLACEMENT REACTIONS
THE DECREASE IN REACTIVITY DOWN THE GROUP IS DEMONSTRATED USING DISPLACEMENT REACTIONS...
A SOLUTION OF THE HALOGEN IS ADDED TO A SOLUTION OF A HALIDE
HALIDES ARE SALTS FORMED FROM HALOGENS (see next slide for examples)
A MORE REACTIVE HALOGEN WILL DISPLACE A LESS REACTIVE ONE
e.g. CHLORINE + SODIUM BROMIDE BROMINE + SODIUM CHLORIDE
CHLORINE + SODIUM IODIDE IODINE + SODIUM CHLORIDE
BROMINE + SODIUM IODIDE IODINE + SODIUM BROMIDE
BUT BROMINE + SODIUM CHLORIDE CHLORINE + SODIUM BROMIDE
(Bromine is below chlorine in the Group so is less reactive)

20. GROUP TRENDS OXIDISING POWER Chlorine oxidises bromide ions to bromine
Cl Br¯ ——> Br Cl¯
Chlorine oxidises iodide ions to iodine
Cl I¯ ——> I Cl¯
Bromine oxidises iodide ions to iodine
Br I¯ ——> I Br¯

21. HALOGENS - DISPLACEMENT REACTIONS DISPLACEMENT REACTIONS - EXPERIMENT
SODIUM CHLORIDE
SODIUM BROMIDE
SODIUM IODIDE
CHLORINE
BROMINE

22. HALOGENS - DISPLACEMENT REACTIONS
DISPLACEMENT REACTIONS - EXPERIMENT
SODIUM CHLORIDE
SODIUM BROMIDE
SODIUM IODIDE
CHLORINE
Solution stays colourless
NO REACTION
Solution goes from colourless to orange-yellow
BROMINE FORMED
Solution goes from colourless to orange-red
IODINE FORMED
BROMINE
Solution goes from colourless to orange-yellow
NO REACTION
Solution goes from colourless to orange-yellow
NO REACTION
Solution goes from colourless to red
IODINE FORMED

23. OTHER REACTIONS OF CHLORINE
Water Halogens react with decreasing vigour down the group as
their oxidising power decreases
Litmus will be turned red then decolourised in chlorine water
Cl2(g) H2O(l) HCl(aq) HOCl(aq) strong acid bleaches by oxidation

24. OTHER REACTIONS OF CHLORINE
Water Halogens react with decreasing vigour down the group as
their oxidising power decreases
Litmus will be turned red then decolourised in chlorine water
Cl2(g) H2O(l) HCl(aq) HOCl(aq) strong acid bleaches by oxidation

25. OTHER REACTIONS OF CHLORINE
Water Halogens react with decreasing vigour down the group as
their oxidising power decreases
Litmus will be turned red then decolourised in chlorine water
Cl2(g) H2O(l) HCl(aq) HOCl(aq) strong acid bleaches by oxidation
This is an example of DISPROPORTIONATION …
‘simultaneous oxidation and reduction of a species’

26. OTHER REACTIONS OF CHLORINE
Water Halogens react with decreasing vigour down the group as
their oxidising power decreases
Litmus will be turned red then decolourised in chlorine water
Cl2(g) H2O(l) HCl(aq) HOCl(aq) strong acid bleaches by oxidation
This is an example of DISPROPORTIONATION …
‘simultaneous oxidation and reduction of a species’
Alkalis Chlorine reacts with cold, aqueous sodium hydroxide.
2NaOH(aq) + Cl2(g) —> NaCl(aq) NaOCl(aq) H2O(l)

27. TESTING FOR HALIDES – AgNO3
• make a solution of the halide
• acidify with dilute nitric acid – this prevents the precipitation of other salts
• add a few drops of silver nitrate solution
• treat any precipitate with dilute ammonia solution
• if a precipitate still exists, add concentrated ammonia solution

28. TESTING FOR HALIDES – AgNO3
CHLORIDE white ppt of AgCl soluble in dilute ammonia
BROMIDE cream ppt of AgBr insoluble in dilute ammonia but soluble in conc.
IODIDE yellow ppt of AgI insoluble in dilute and
conc. ammonia solution

29. TESTING FOR HALIDES – AgNO3
CHLORIDE white ppt of AgCl soluble in dilute ammonia
BROMIDE cream ppt of AgBr insoluble in dilute ammonia but soluble in conc.
IODIDE yellow ppt of AgI insoluble in dilute and
conc. ammonia solution
halides precipitate as follows Ag+(aq) + X¯(aq) ——> Ag+X¯(s)
when they dissolve in ammonia a colourless diammine complex is formed [Ag(NH3)2]+(aq)

30. TESTING FOR HALIDES – AgNO3
CHLORIDE
BROMIDE
IODIDE
PLACE A SOLUTION OF THE HALIDE IN A TEST TUBE

31. TESTING FOR HALIDES – AgNO3 ADD SOME DILUTE NITRIC ACID
CHLORIDE
BROMIDE
IODIDE
ADD SOME DILUTE NITRIC ACID

32. TESTING FOR HALIDES – AgNO3 ADD SILVER NITRATE SOLUTION
CHLORIDE
BROMIDE
IODIDE
ADD SILVER NITRATE SOLUTION
WHITE PRECIPITATE OF SILVER CHLORIDE AgCl
CREAM PRECIPITATE OF SILVER BROMIDE AgBr
YELLOW PRECIPITATE OF SILVER IODIDE AgI

33. TESTING FOR HALIDES – AgNO3 ADD DILUTE AMMONIA SOLUTION
CHLORIDE
BROMIDE
IODIDE
ADD DILUTE AMMONIA SOLUTION
WHITE PRECIPITATE OF SILVER CHLORIDE - SOLUBLE
CREAM PRECIPITATE OF SILVER BROMIDE - INSOLUBLE
YELLOW PRECIPITATE OF SILVER IODIDE - INSOLUBLE

34. TESTING FOR HALIDES – AgNO3 ADD CONCENTRATED AMMONIA SOLUTION
CHLORIDE
BROMIDE
IODIDE
ADD CONCENTRATED AMMONIA SOLUTION
WHITE PRECIPITATE OF SILVER CHLORIDE - SOLUBLE
CREAM PRECIPITATE OF SILVER BROMIDE - SOLUBLE
YELLOW PRECIPITATE OF SILVER IODIDE - INSOLUBLE

35. TESTING FOR HALIDES – Conc. H2SO4
• an alternative test for halides
• add concentrated sulphuric acid carefully to a solid halide
• H2SO4 displaces the weaker acids HCl, HBr, and HI from their salts
• as they become more powerful reducing agents down the group
they can react further by reducing the sulphuric acid to lower
oxidation states of sulphur

36. TESTING FOR HALIDES – Conc. H2SO4
Summary
Halide Observation(s) Product O.S. Reaction type
NaCl misty fumes HCl -1 Displacement of Cl¯
NaBr misty fumes HBr -1 Displacement of Br¯
brown vapour Br2 0 Oxidation of Br¯
colourless gas SO2 +4 Reduction of H2SO4
NaI misty fumes HI -1 Displacement of I¯
purple vapour I2 0 Oxidation of I¯
colourless gas SO2 +4 Reduction of H2SO4
yellow solid S 0 Reduction of H2SO4
bad egg smell H2S -2 Reduction of H2SO4

37. HYDROGEN HALIDES - PROPERTIES
Boiling points At room temp. and pressure HCl, HBr, HI are
colourless gases, HF a colourless liquid.
b. pts ... HF 20°C HCl -85°C HBr -69°C HI -35°C
HF value is higher than expected due to hydrogen bonding

38. HYDROGEN HALIDES - PROPERTIES
Boiling points At room temp. and pressure HCl, HBr, HI are
colourless gases, HF a colourless liquid.
b. pts ... HF 20°C HCl -85°C HBr -69°C HI -35°C
HF value is higher than expected due to hydrogen bonding
Reducing
ability Increases down the group as bond strength decreases
bond energy H-F H-Cl H-Br H-I 298
/ kJ mol-1

39. HYDROGEN HALIDES - PREPARATION
Direct
combination Hydrogen halides can be made by direct combination
H2(g) X2(g) ——> 2HX(g)
• fluorine combines explosively, even in the dark
• chlorine combines explosively when heated or in sunlight
• bromine is fast at 200°C with a catalyst
• iodine reaction is reversible.

40. HYDROGEN HALIDES - PREPARATION
Direct
combination Hydrogen halides can be made by direct combination
H2(g) X2(g) ——> 2HX(g)
• fluorine combines explosively, even in the dark
• chlorine combines explosively when heated or in sunlight
• bromine is fast at 200°C with a catalyst
• iodine reaction is reversible.
Displacement Chlorides are made by displacing the acid from its salt
NaCl(s) conc. H2SO4(l) ——> NaHSO4(s) + HCl(g)

41. HYDROGEN HALIDES - PREPARATION
Direct
combination Hydrogen halides can be made by direct combination
H2(g) X2(g) ——> 2HX(g)
• fluorine combines explosively, even in the dark
• chlorine combines explosively when heated or in sunlight
• bromine is fast at 200°C with a catalyst
• iodine reaction is reversible.
Displacement Chlorides are made by displacing the acid from its salt
NaCl(s) conc. H2SO4(l) ——> NaHSO4(s) + HCl(g)
HBr and HI are not made this way as they are more powerful
reducing agents and are oxidised by sulphuric acid to the halogen
2HBr(g) conc. H2SO4(l) ——> 2H2O(l) + SO2(g) + Br2(g)

42. HALOGENS & HALIDES - USES
Chlorine, Cl2 • water purification
• bleach
• solvents
• polymers - poly(chloroethene) or PVC
• CFC’s
Fluorine, F2 • CFC’s
• polymers - PTFE poly(tetrafluoroethene) as used in...
non-stick frying pans, electrical insulation,
waterproof clothing
Fluoride, F¯ • helps prevent tooth decay
- tin fluoride is added to toothpaste
- sodium fluoride is added to water supplies
Hydrogen
fluoride, HF • used to etch glass
Silver
bromide, AgBr • used in photographic film

43. VOLUMETRIC ANALYSIS OF CHLORATE(I)
Introduction Chlorate(I) ions are oxidising agents
In acid solution they end up as chloride ions
ClO¯ H e¯ ——> Cl¯ H2O

44. VOLUMETRIC ANALYSIS OF CHLORATE(I)
Introduction Chlorate(I) ions are oxidising agents
In acid solution they end up as chloride ions
ClO¯ H e¯ ——> Cl¯ H2O
Oxidation state -1

45. VOLUMETRIC ANALYSIS OF CHLORATE(I)
Introduction Chlorate(I) ions are oxidising agents
In acid solution they end up as chloride ions
ClO¯ H e¯ ——> Cl¯ H2O
Analysis (1) Add excess potassium iodide;
the chlorate oxidises the iodide ions to iodine
ClO¯ H e¯ ——> Cl¯ H2O
2I¯ ——> I e¯

46. VOLUMETRIC ANALYSIS OF CHLORATE(I)
Introduction Chlorate(I) ions are oxidising agents
In acid solution they end up as chloride ions
ClO¯ H e¯ ——> Cl¯ H2O
Analysis (1) Add excess potassium iodide;
the chlorate oxidises the iodide ions to iodine
ClO¯ H e¯ ——> Cl¯ H2O
2I¯ ——> I e¯
overall ClO¯ H I¯ ——> I Cl¯ H2O
moles of I2 produced = original moles of OCl¯ -- (i)

47. VOLUMETRIC ANALYSIS OF CHLORATE(I)
Introduction Chlorate(I) ions are oxidising agents
In acid solution they end up as chloride ions
ClO¯ H e¯ ——> Cl¯ H2O
Analysis (2) Titrate the iodine produced with sodium thiosulphate
using starch as the indicator near the end point
2S2O32- ——> S4O e¯
I e¯ ——> 2I¯

48. VOLUMETRIC ANALYSIS OF CHLORATE(I)
Introduction Chlorate(I) ions are oxidising agents
In acid solution they end up as chloride ions
ClO¯ H e¯ ——> Cl¯ H2O
Analysis (2) Titrate the iodine produced with sodium thiosulphate
using starch as the indicator near the end point
2S2O32- ——> S4O e¯
I e¯ ——> 2I¯
overall I S2O32- ——> S4O I¯

49. VOLUMETRIC ANALYSIS OF CHLORATE(I)
Introduction Chlorate(I) ions are oxidising agents
In acid solution they end up as chloride ions
ClO¯ H e¯ ——> Cl¯ H2O
Analysis (2) Titrate the iodine produced with sodium thiosulphate
using starch as the indicator near the end point
2S2O32- ——> S4O e¯
I e¯ ——> 2I¯
overall I S2O32- ——> S4O I¯
moles of I2 = ½ x moles of S2O (ii)
from (i) and (ii) original moles of OCl¯ = ½ x moles of S2O32-

50. ©2008 JONATHAN HOPTON & KNOCKHARDY PUBLISHING
AN INTRODUCTION TO
GROUP VII
THE END
©2008 JONATHAN HOPTON & KNOCKHARDY PUBLISHING