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Periodicity is a regular periodic variation of properties of elements with atomic number and positions in the periodic table.

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Presentation on theme: "Periodicity is a regular periodic variation of properties of elements with atomic number and positions in the periodic table."— Presentation transcript:

1 Periodicity is a regular periodic variation of properties of elements with atomic number and positions in the periodic table.

2 Group 7:redox, uses and halide tests. L.O.: Explain the trend in boiling points of Cl 2, Br 2 and I 2. 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

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5 Electronic configurations of halogen atoms

6 GROUP TRENDS Cl 2 + 2e - → 2Cl - halogens are oxidising agents they need one electron to complete their octet OXIDISING POWER

7 GROUP 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 POWER

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

9 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

10 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

11 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 Cl 2 (aq) + 2NaBr(aq) ——> Br 2 (aq) + 2NaCl(aq)

12 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 Cl 2 (aq) + 2Br¯(aq) ——> Br 2 (aq) + 2Cl¯(aq) Cl 2 (aq) + 2NaBr(aq) ——> Br 2 (aq) + 2NaCl(aq)

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 e.g.CHLORINE + SODIUM BROMIDE BROMINE + SODIUM CHLORIDE CHLORINE + SODIUM IODIDE IODINE + SODIUM CHLORIDE

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 CHLORINE + SODIUM IODIDE IODINE + SODIUM CHLORIDE BROMINE + SODIUM IODIDE IODINE + SODIUM BROMIDE

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 CHLORINE + SODIUM IODIDE IODINE + SODIUM CHLORIDE BROMINE + SODIUM IODIDE IODINE + SODIUM BROMIDE BUTBROMINE + SODIUM CHLORIDE CHLORINE + SODIUM BROMIDE (Bromine is below chlorine in the Group so is less reactive)

16 GROUP TRENDS Chlorine oxidises bromide ions to bromine Cl 2 + 2Br¯ ——> Br 2 + 2Cl¯ Chlorine oxidises iodide ions to iodine Cl 2 + 2I¯ ——> I 2 + 2Cl¯ Bromine oxidises iodide ions to iodine Br 2 + 2I¯ ——> I 2 + 2Br¯ OXIDISING POWER

17 Look at Figure 4 in page 93

18 Disproportionation: a reaction in which the same element is both reduced and oxidised. Cl 2 (g) + H 2 O(l) → HClO(aq) + HCl(aq) Production of bleach: Cl 2 (aq) + NaOH(aq)→ NaCl(aq) + NaClO(aq) + H 2 O(l)

19 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.

20 TESTING FOR HALIDES – AgNO 3 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

21 TESTING FOR HALIDES – AgNO 3 CHLORIDEwhite ppt of AgC l soluble in dilute ammonia BROMIDEcream ppt of AgBrinsoluble in dilute ammonia but soluble in conc. IODIDEyellow ppt of AgI insoluble in dilute and conc. ammonia solution

22 TESTING FOR HALIDES – AgNO 3 CHLORIDEwhite ppt of AgClsoluble in dilute ammonia BROMIDEcream ppt of AgBrinsoluble in dilute ammonia but soluble in conc. IODIDEyellow 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(NH 3 ) 2 ] + (aq)

23 PLACE A SOLUTION OF THE HALIDE IN A TEST TUBE CHLORIDEBROMIDEIODIDE TESTING FOR HALIDES – AgNO 3

24 ADD SOME DILUTE NITRIC ACID CHLORIDEBROMIDEIODIDE TESTING FOR HALIDES – AgNO 3

25 ADD SILVER NITRATE SOLUTION WHITE PRECIPITATE OF SILVER CHLORIDE AgC l CREAM PRECIPITATE OF SILVER BROMIDE AgBr YELLOW PRECIPITATE OF SILVER IODIDE AgI CHLORIDEBROMIDEIODIDE TESTING FOR HALIDES – AgNO 3

26 ADD DILUTE AMMONIA SOLUTION WHITE PRECIPITATE OF SILVER CHLORIDE - SOLUBLE CREAM PRECIPITATE OF SILVER BROMIDE - INSOLUBLE YELLOW PRECIPITATE OF SILVER IODIDE - INSOLUBLE CHLORIDEBROMIDEIODIDE TESTING FOR HALIDES – AgNO 3

27 ADD CONCENTRATED AMMONIA SOLUTION WHITE PRECIPITATE OF SILVER CHLORIDE - SOLUBLE CREAM PRECIPITATE OF SILVER BROMIDE - SOLUBLE YELLOW PRECIPITATE OF SILVER IODIDE - INSOLUBLE CHLORIDEBROMIDEIODIDE TESTING FOR HALIDES – AgNO 3


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