Periodicity is a regular periodic variation of
properties of elements with atomic number
and positions in the periodic table.
Group 7:redox, uses and halide tests.
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L.O.:
Explain the trend in boiling points of Cl2, Br2 and
I2.
Explain the trend in reactivity for the Group 7
elements.
Describe the redox reactions of the Group 7
elements with other halide ions.
Describe and interpret, using oxidation numbers,
the reaction of chlorine with water and aqueous
sodium hydroxide
Electronic configurations of halogen atoms
GROUP TRENDS
OXIDISING POWER
Cl2 + 2e- → 2Clhalogens are oxidising agents
• they need one electron to complete their octet
GROUP TRENDS
OXIDISING POWER
• halogens are oxidising agents
• they need one electron to complete their octet
• the oxidising power gets weaker down the group
•Going down a group..
• increasing nuclear charge which should attract electrons more
but this is offset by
• INCREASED SHIELDING
• INCREASING ATOMIC RADIUS
The oxidising ability of the halogens decreases as we go up
the group
HALOGENS - DISPLACEMENT REACTIONS
THE DECREASE IN REACTIVITY DOWN THE GROUP IS DEMONSTRATED USING
DISPLACEMENT REACTIONS...
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
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
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) + 2NaBr(aq) ——> Br2(aq) + 2NaCl(aq)
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) + 2NaBr(aq) ——> Br2(aq) + 2NaCl(aq)
Cl2(aq) + 2Br¯(aq) ——> Br2(aq) + 2Cl¯(aq)
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
CHLORINE + SODIUM IODIDE
BROMINE + SODIUM CHLORIDE
IODINE + SODIUM CHLORIDE
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
CHLORINE + SODIUM IODIDE
BROMINE + SODIUM IODIDE
BROMINE + SODIUM CHLORIDE
IODINE + SODIUM CHLORIDE
IODINE + SODIUM BROMIDE
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
CHLORINE + SODIUM IODIDE
BROMINE + SODIUM IODIDE
BUT
BROMINE + SODIUM CHLORIDE
BROMINE + SODIUM CHLORIDE
IODINE + SODIUM CHLORIDE
IODINE + SODIUM BROMIDE
CHLORINE + SODIUM BROMIDE
(Bromine is below chlorine in the Group so is less reactive)
GROUP TRENDS
OXIDISING POWER
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¯
Look at Figure 4 in page 93
Disproportionation: a reaction in which the same
element is both reduced and oxidised.
Cl2(g) + H2O(l) → HClO(aq) + HCl(aq)
Production of bleach:
Cl2(aq) + NaOH(aq)→ NaCl(aq) + NaClO(aq) +
H2O(l)
L.O.:
Describe the precipitation reactions of
aqueous anions Cl–, Br– and I– with aqueous
silver ions, followed by aqueous ammonia.
Recognise the use of these precipitation
reactions as a test for different halide ions.
TESTING FOR HALIDES – AgNO3
• make a solution of the halide
• acidify with dilute nitric acid – this prevents the precipitation of other salts.
It get rids of carbonates and hydroxides.
• 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 – 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
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 AgIinsoluble 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)
TESTING FOR HALIDES – AgNO3
CHLORIDE
BROMIDE
IODIDE
PLACE A SOLUTION OF THE HALIDE IN A TEST TUBE
TESTING FOR HALIDES – AgNO3
CHLORIDE
BROMIDE
ADD SOME DILUTE NITRIC ACID
IODIDE
TESTING FOR HALIDES – AgNO3
CHLORIDE
BROMIDE
IODIDE
ADD SILVER NITRATE SOLUTION
WHITE PRECIPITATE OF SILVER CHLORIDE
CREAM PRECIPITATE OF SILVER BROMIDE
YELLOW PRECIPITATE OF SILVER IODIDE
AgCl
AgBr
AgI
TESTING FOR HALIDES – AgNO3
CHLORIDE
BROMIDE
IODIDE
ADD DILUTE AMMONIA SOLUTION
WHITE PRECIPITATE OF SILVER CHLORIDE
CREAM PRECIPITATE OF SILVER BROMIDE
YELLOW PRECIPITATE OF SILVER IODIDE
- SOLUBLE
- INSOLUBLE
- INSOLUBLE
TESTING FOR HALIDES – AgNO3
CHLORIDE
BROMIDE
IODIDE
ADD CONCENTRATED AMMONIA SOLUTION
WHITE PRECIPITATE OF SILVER CHLORIDE
CREAM PRECIPITATE OF SILVER BROMIDE
YELLOW PRECIPITATE OF SILVER IODIDE
- SOLUBLE
- SOLUBLE
- INSOLUBLE