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AN INTRODUCTION TOAN INTRODUCTION TO
GROUP VIIGROUP VII
KNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING2008 2008
SPECIFICATIONSSPECIFICATIONS
INTRODUCTION
This Powerpoint show is one of several produced to help students understand selected topics at AS and A2 level Chemistry. It is based on the requirements of the AQA and OCR specifications but is suitable for other examination boards.
Individual students may use the material at home for revision purposes or it may be used for classroom teaching with an interactive white board.
Accompanying notes on this, and the full range of AS and A2 topics, are available from the KNOCKHARDY SCIENCE WEBSITE at...
www.knockhardy.org.uk/sci.htm
Navigation is achieved by...
either clicking on the grey arrows at the foot of each page
or using the left and right arrow keys on the keyboard
KNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING
GROUP 7 (HALOGENS)GROUP 7 (HALOGENS)
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
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
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
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
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
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
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
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
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
HALOGENS - DISPLACEMENT REACTIONSHALOGENS - DISPLACEMENT REACTIONS
THE DECREASE IN REACTIVITY DOWN THE GROUP IS DEMONSTRATED USING DISPLACEMENT REACTIONS...
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
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
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)
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)
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
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
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)
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
SODIUM CHLORIDE
DISPLACEMENT REACTIONS - EXPERIMENT
HALOGENS - DISPLACEMENT REACTIONSHALOGENS - DISPLACEMENT REACTIONS
CHLORINE
SODIUM BROMIDE SODIUM IODIDE
BROMINE
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
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
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
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
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
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
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 andconc. ammonia solution
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 andconc. 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)
PLACE A SOLUTION OF THE HALIDE IN A TEST TUBE
CHLORIDE BROMIDE IODIDE
TESTING FOR HALIDES – AgNOTESTING FOR HALIDES – AgNO33
ADD SOME DILUTE NITRIC ACID
CHLORIDE BROMIDE IODIDE
TESTING FOR HALIDES – AgNOTESTING FOR HALIDES – AgNO33
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
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
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
• 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
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
HYDROGEN HALIDES - PROPERTIESHYDROGEN HALIDES - PROPERTIES
Boiling points At room temp. and pressure HCl, HBr, HI arecolourless 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
HYDROGEN HALIDES - PROPERTIESHYDROGEN HALIDES - PROPERTIES
Boiling points At room temp. and pressure HCl, HBr, HI arecolourless 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
Reducingability 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
HYDROGEN HALIDES - PREPARATIONHYDROGEN HALIDES - PREPARATION
Directcombination 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.
HYDROGEN HALIDES - PREPARATIONHYDROGEN HALIDES - PREPARATION
Directcombination 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)
HYDROGEN HALIDES - PREPARATIONHYDROGEN HALIDES - PREPARATION
Directcombination 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 powerfulreducing agents and are oxidised by sulphuric acid to the halogen
2HBr(g) + conc. H2SO4(l) ——> 2H2O(l) + SO2(g) + Br2(g)
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
Hydrogenfluoride, HF • used to etch glass
Silverbromide, AgBr • used in photographic film
VOLUMETRIC ANALYSIS OF CHLORATE(I)VOLUMETRIC ANALYSIS OF CHLORATE(I)
Introduction Chlorate(I) ions are oxidising agentsIn acid solution they end up as chloride ions
ClO¯ + 2H+ + 2e¯ ——> Cl¯ + H2O
VOLUMETRIC ANALYSIS OF CHLORATE(I)VOLUMETRIC ANALYSIS OF CHLORATE(I)
Introduction Chlorate(I) ions are oxidising agentsIn acid solution they end up as chloride ions
ClO¯ + 2H+ + 2e¯ ——> Cl¯ + H2OOxidation state +1 -1
VOLUMETRIC ANALYSIS OF CHLORATE(I)VOLUMETRIC ANALYSIS OF CHLORATE(I)
Introduction Chlorate(I) ions are oxidising agentsIn 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¯
VOLUMETRIC ANALYSIS OF CHLORATE(I)VOLUMETRIC ANALYSIS OF CHLORATE(I)
Introduction Chlorate(I) ions are oxidising agentsIn 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)
VOLUMETRIC ANALYSIS OF CHLORATE(I)VOLUMETRIC ANALYSIS OF CHLORATE(I)
Introduction Chlorate(I) ions are oxidising agentsIn acid solution they end up as chloride ions
ClO¯ + 2H+ + 2e¯ ——> Cl¯ + H2O
Analysis (2) Titrate the iodine produced with sodium thiosulphateusing starch as the indicator near the end point
2S2O32- ——> S4O6
2- + 2e¯
I2 + 2e¯ ——> 2I¯
VOLUMETRIC ANALYSIS OF CHLORATE(I)VOLUMETRIC ANALYSIS OF CHLORATE(I)
Introduction Chlorate(I) ions are oxidising agentsIn acid solution they end up as chloride ions
ClO¯ + 2H+ + 2e¯ ——> Cl¯ + H2O
Analysis (2) Titrate the iodine produced with sodium thiosulphateusing starch as the indicator near the end point
2S2O32- ——> S4O6
2- + 2e¯
I2 + 2e¯ ——> 2I¯
overall I2 + 2S2O32- ——> S4O6
2- + 2I¯
VOLUMETRIC ANALYSIS OF CHLORATE(I)VOLUMETRIC ANALYSIS OF CHLORATE(I)
Introduction Chlorate(I) ions are oxidising agentsIn acid solution they end up as chloride ions
ClO¯ + 2H+ + 2e¯ ——> Cl¯ + H2O
Analysis (2) Titrate the iodine produced with sodium thiosulphateusing starch as the indicator near the end point
2S2O32- ——> S4O6
2- + 2e¯
I2 + 2e¯ ——> 2I¯
overall I2 + 2S2O32- ——> S4O6
2- + 2I¯
moles of I2 = ½ x moles of S2O32- -- (ii)
from (i) and (ii) original moles of OCl¯ = ½ x moles of S2O32-
©2008 JONATHAN HOPTON & KNOCKHARDY PUBLISHING©2008 JONATHAN HOPTON & KNOCKHARDY PUBLISHING
THE ENDTHE END
AN INTRODUCTION TOAN INTRODUCTION TO
GROUP VIIGROUP VII