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

OXIDISING POWER GROUP TRENDS Cl2 + 2e- → 2Cl- halogens are oxidising agents • they need one electron to complete their octet

The oxidising ability of the halogens decreases as we go up the group 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 BROMINE + SODIUM CHLORIDE CHLORINE + SODIUM IODIDE 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 BROMINE + SODIUM CHLORIDE CHLORINE + SODIUM IODIDE IODINE + SODIUM CHLORIDE BROMINE + SODIUM IODIDE 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 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)

Chlorine oxidises bromide ions to bromine Cl2 + 2Br¯ ——> Br2 + 2Cl¯ 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 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)

TESTING FOR HALIDES – AgNO3 CHLORIDE BROMIDE IODIDE PLACE A SOLUTION OF THE HALIDE IN A TEST TUBE

TESTING FOR HALIDES – AgNO3 ADD SOME DILUTE NITRIC ACID CHLORIDE BROMIDE IODIDE ADD SOME DILUTE NITRIC ACID

TESTING FOR HALIDES – AgNO3 ADD SILVER NITRATE SOLUTION CHLORIDE BROMIDE IODIDE ADD SILVER NITRATE SOLUTION WHITE PRECIPITATE OF SILVER CHLORIDE AgCl CREAM PRECIPITATE OF SILVER BROMIDE AgBr YELLOW PRECIPITATE OF SILVER IODIDE AgI

TESTING FOR HALIDES – AgNO3 ADD DILUTE AMMONIA SOLUTION CHLORIDE BROMIDE IODIDE ADD DILUTE AMMONIA SOLUTION WHITE PRECIPITATE OF SILVER CHLORIDE - SOLUBLE CREAM PRECIPITATE OF SILVER BROMIDE - INSOLUBLE YELLOW PRECIPITATE OF SILVER IODIDE - INSOLUBLE

TESTING FOR HALIDES – AgNO3 ADD CONCENTRATED AMMONIA SOLUTION CHLORIDE BROMIDE IODIDE ADD CONCENTRATED AMMONIA SOLUTION WHITE PRECIPITATE OF SILVER CHLORIDE - SOLUBLE CREAM PRECIPITATE OF SILVER BROMIDE - SOLUBLE YELLOW PRECIPITATE OF SILVER IODIDE - INSOLUBLE