explaining the properties of group vii elements

1. AN INTRODUCTION TOAN INTRODUCTION TO
GROUP VIIGROUP VII
KNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING
20082008
SPECIFICATIONSSPECIFICATIONS

2. INTRODUCTION
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KNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING
GROUP 7 (HALOGENS)GROUP 7 (HALOGENS)

3. 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
GROUP VIIGROUP VII

4. GROUP PROPERTIESGROUP PROPERTIES
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
• atomic size
• oxidising power

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

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

7. GROUP TRENDSGROUP TRENDS
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
F Cl Br I
ATOMIC & IONIC RADIUSATOMIC & IONIC RADIUS
0.064 0.099 0.111 0.128Atomic radius / nm
F¯ Cl¯ Br¯ I¯
0.136 0.181 0.195 0.216Ionic radius / nm

8. GROUP TRENDSGROUP TRENDS
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
F Cl Br I
ELECTRONEGATIVITYELECTRONEGATIVITY
4.0 3.5 2.8 2.5Electronegativity

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

10. GROUP TRENDSGROUP TRENDS
• 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
OXIDISING POWEROXIDISING POWER

11. GROUP TRENDSGROUP TRENDS
• 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.
OXIDISING POWEROXIDISING POWER

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

13. HALOGENS - DISPLACEMENT REACTIONSHALOGENS - 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 REACTIONSHALOGENS - 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 REACTIONSHALOGENS - 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) + 2NaBr(aq) ——> Br2(aq) + 2NaCl(aq)

16. HALOGENS - DISPLACEMENT REACTIONSHALOGENS - 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) + 2Br¯(aq) ——> Br2(aq) + 2Cl¯(aq)
Cl2(aq) + 2NaBr(aq) ——> Br2(aq) + 2NaCl(aq)

17. HALOGENS - DISPLACEMENT REACTIONSHALOGENS - 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 REACTIONSHALOGENS - 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 REACTIONSHALOGENS - 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 TRENDSGROUP TRENDS
Chlorine oxidises bromide ions to bromine
Cl2 + 2Br¯ ——> Br2 + 2Cl¯
Chlorine oxidises iodide ions to iodine
Cl2 + 2I¯ ——> I2 + 2Cl¯
Bromine oxidises iodide ions to iodine
Br2 + 2I¯ ——> I2 + 2Br¯
OXIDISING POWEROXIDISING POWER

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

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

23. OTHER REACTIONS OF CHLORINEOTHER 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 CHLORINEOTHER 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
0 -1 +1

25. OTHER REACTIONS OF CHLORINEOTHER 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’
0 -1 +1

26. OTHER REACTIONS OF CHLORINEOTHER 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)
0 -1 +1

27. TESTING FOR HALIDES – AgNOTESTING FOR HALIDES – AgNO33
• 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 – AgNOTESTING FOR HALIDES – AgNO33
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 – AgNOTESTING FOR HALIDES – AgNO33
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. PLACE A SOLUTION OF THE HALIDE IN A TEST TUBE
CHLORIDE BROMIDE IODIDE
TESTING FOR HALIDES – AgNOTESTING FOR HALIDES – AgNO33

31. ADD SOME DILUTE NITRIC ACID
CHLORIDE BROMIDE IODIDE
TESTING FOR HALIDES – AgNOTESTING FOR HALIDES – AgNO33

32. ADD SILVER NITRATE SOLUTION
WHITE PRECIPITATE OF SILVER CHLORIDE AgCl
CREAM PRECIPITATE OF SILVER BROMIDE AgBr
YELLOW PRECIPITATE OF SILVER IODIDE AgI
CHLORIDE BROMIDE IODIDE
TESTING FOR HALIDES – AgNOTESTING FOR HALIDES – AgNO33

33. ADD DILUTE AMMONIA SOLUTION
WHITE PRECIPITATE OF SILVER CHLORIDE - SOLUBLE
CREAM PRECIPITATE OF SILVER BROMIDE - INSOLUBLE
YELLOW PRECIPITATE OF SILVER IODIDE - INSOLUBLE
CHLORIDE BROMIDE IODIDE
TESTING FOR HALIDES – AgNOTESTING FOR HALIDES – AgNO33

34. ADD CONCENTRATED AMMONIA SOLUTION
WHITE PRECIPITATE OF SILVER CHLORIDE - SOLUBLE
CREAM PRECIPITATE OF SILVER BROMIDE - SOLUBLE
YELLOW PRECIPITATE OF SILVER IODIDE - INSOLUBLE
CHLORIDE BROMIDE IODIDE
TESTING FOR HALIDES – AgNOTESTING FOR HALIDES – AgNO33

35. • 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
TESTING FOR HALIDES – Conc. HTESTING FOR HALIDES – Conc. H22SOSO44

36. SummarySummary
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
TESTING FOR HALIDES – Conc. HTESTING FOR HALIDES – Conc. H22SOSO44

37. HYDROGEN HALIDES - PROPERTIESHYDROGEN 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 - PROPERTIESHYDROGEN 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 568 H-Cl 432 H-Br 366 H-I 298
/ kJ mol-1

39. HYDROGEN HALIDES - PREPARATIONHYDROGEN 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 - PREPARATIONHYDROGEN 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 - PREPARATIONHYDROGEN 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 - USESHALOGENS & 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)VOLUMETRIC ANALYSIS OF CHLORATE(I)
Introduction Chlorate(I) ions are oxidising agents
In acid solution they end up as chloride ions
ClO¯ + 2H+
+ 2e¯ ——> Cl¯ + H2O

44. VOLUMETRIC ANALYSIS OF CHLORATE(I)VOLUMETRIC ANALYSIS OF CHLORATE(I)
Introduction Chlorate(I) ions are oxidising agents
In acid solution they end up as chloride ions
ClO¯ + 2H+
+ 2e¯ ——> Cl¯ + H2O
Oxidation state +1 -1

45. VOLUMETRIC ANALYSIS OF CHLORATE(I)VOLUMETRIC ANALYSIS OF CHLORATE(I)
Introduction Chlorate(I) ions are oxidising agents
In acid solution they end up as chloride ions
ClO¯ + 2H+
+ 2e¯ ——> Cl¯ + H2O
Analysis (1) Add excess potassium iodide;
the chlorate oxidises the iodide ions to iodine
ClO¯ + 2H+
+ 2e¯ ——> Cl¯ + H2O
2I¯ ——> I2 + 2e¯

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

47. VOLUMETRIC ANALYSIS OF CHLORATE(I)VOLUMETRIC ANALYSIS OF CHLORATE(I)
Introduction Chlorate(I) ions are oxidising agents
In acid solution they end up as chloride ions
ClO¯ + 2H+
+ 2e¯ ——> Cl¯ + H2O
Analysis (2) Titrate the iodine produced with sodium thiosulphate
using starch as the indicator near the end point
2S2O3
2-
——> S4O6
2-
+ 2e¯
I2 + 2e¯ ——> 2I¯

48. VOLUMETRIC ANALYSIS OF CHLORATE(I)VOLUMETRIC ANALYSIS OF CHLORATE(I)
Introduction Chlorate(I) ions are oxidising agents
In acid solution they end up as chloride ions
ClO¯ + 2H+
+ 2e¯ ——> Cl¯ + H2O
Analysis (2) Titrate the iodine produced with sodium thiosulphate
using starch as the indicator near the end point
2S2O3
2-
——> S4O6
2-
+ 2e¯
I2 + 2e¯ ——> 2I¯
overall I2 + 2S2O3
2-
——> S4O6
2-
+ 2I¯

49. VOLUMETRIC ANALYSIS OF CHLORATE(I)VOLUMETRIC ANALYSIS OF CHLORATE(I)
Introduction Chlorate(I) ions are oxidising agents
In acid solution they end up as chloride ions
ClO¯ + 2H+
+ 2e¯ ——> Cl¯ + H2O
Analysis (2) Titrate the iodine produced with sodium thiosulphate
using starch as the indicator near the end point
2S2O3
2-
——> S4O6
2-
+ 2e¯
I2 + 2e¯ ——> 2I¯
overall I2 + 2S2O3
2-
——> S4O6
2-
+ 2I¯
moles of I2 = ½ x moles of S2O3
2-
-- (ii)
from (i) and (ii) original moles of OCl¯ = ½ x moles of S2O3
2-

50. ©2008 JONATHAN HOPTON & KNOCKHARDY PUBLISHING©2008 JONATHAN HOPTON & KNOCKHARDY PUBLISHING
THETHE
ENDEND
AN INTRODUCTION TOAN INTRODUCTION TO
GROUP VIIGROUP VII