periodicity is a regular periodic variation of properties of elements with atomic number and...
TRANSCRIPT
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.
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 TRENDSGROUP TRENDS
Cl2 + 2e- → 2Cl-
halogens are oxidising agents• they need one electron to complete their octet
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
•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
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
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 – AgNOTESTING FOR HALIDES – AgNO33
• 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 – 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 AgClCREAM 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