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Lesson 1 Group 7 Elements Eam

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A-level chemistry

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Lesson 1 Group 7 Elements Eam

  1. 1. Group 7 Chemistry. (The Halogens) Aim: To identify and explain the physical trends in group 7. To recognise the tests for Chlorine, Bromine and Iodine. To explain the chemistry of the reactions of Group 7 and Group 1 metals. To Identify the tests for chloride, bromide and iodide ions.
  2. 2. The Halogens………. What do you know about the halogens from Year 10 and 11? Any special properties of the halogens?
  3. 3. Halogen Trends 183 Iodine 58 Bromine -34 Chlorine -188 Fluorine Boiling point in degrees C Colour. State at room temp. Formula. Halogen.
  4. 4. Tests for Halogens Turns starch SOLUTION blue black. Gives a purple colour in an organic solvent . Iodine Bleaches damp blue litmus paper slowly. Bromine will also turn a colourless solution of potassium iodide red brown Bromine Bleaches damp blue litmus paper quickly. Chlorine will also turn a solution of colourless potassium bromide brown. Chlorine Test Halogen
  5. 5. Identifying and Explaining trends <ul><li>Describe the trend in appearance as atomic number increases. </li></ul><ul><li>Describe the trend in boiling point as atomic number increases. </li></ul><ul><li>What type of intermolecular forces exist between the halogen molecules? </li></ul><ul><li>What causes these forces? </li></ul><ul><li>Why do these forces become stronger as the atomic number increases? </li></ul>
  6. 6. Trends in Atomic Radii. <ul><li>Why does atomic radii increase as atomic number increases? </li></ul>
  7. 7. Reactions of the Halogens with Group 1 Metals. <ul><li>Reaction with Group 1 metals. </li></ul><ul><li>2Na + Cl 2 2NaCl </li></ul><ul><li>Reaction type? </li></ul><ul><li>Ionic half equations for the reaction </li></ul><ul><li>Sodium? </li></ul><ul><li>Chlorine? </li></ul><ul><li>Overall redox equation. </li></ul><ul><li>Oxidising agent? ( an atom, ion or molecule that oxidises another by removing one or more electrons) </li></ul>
  8. 8. Trends in 1 st electron affinity. <ul><li>Define the term 1st electron affinity. </li></ul><ul><li>The energy change when I mole of electrons is added to mole of gaseous atoms. </li></ul><ul><li>Cl(g) + e - Cl -1 </li></ul><ul><li>Why do electron affinity values decrease down the group? </li></ul><ul><li>The electron is not brought as close to the nucleus so energy release is less. </li></ul><ul><li>Why is F an exception? </li></ul><ul><li>The atom is so small that the repulsion between the outer electrons and the in coming electron reduces the energy released by the attraction of the nucleus. </li></ul>Decreasing energy release -314 I -342 Br -364 Cl -348 F Electron affinity kJ mol -1 Halogen
  9. 9. Group 2 <ul><li>Reaction of Mg and Chlorine </li></ul><ul><li>Mg + Br 2 MgBr 2 </li></ul><ul><li>Ionic half equations </li></ul><ul><li>Magnesium </li></ul><ul><li>Bromine </li></ul><ul><li>Overall redox equation </li></ul><ul><li>Oxidising agent? </li></ul>
  10. 10. Testing and Identifying Halide Ions Aim:To identify the conclusive chemical tests for Halide ions.
  11. 11. Chloride Cl -1 ;Bromide Br -1 ;Iodide I -1 <ul><li>Add about 2ml of aqueous chloride to a test tube </li></ul><ul><li>Add an equal volume of dilute HNO 3 </li></ul><ul><li>Add a few drops of silver (I) nitrate to the tube </li></ul><ul><li>Pour half of the contents of the tube into a clean test tube </li></ul><ul><li>To the 1 st tube add dilute ammonia until no further change </li></ul><ul><li>To the second tube add CONC AMMONIA until there is no further change – Do this in a fume cupborad </li></ul><ul><li>Repeat with aqueous solutions of bromide and iodide </li></ul>
  12. 12. Results Table I -1 Br -1 Cl -1 Action of conc NH 3 on product Action of dilute NH 3 on product HNO 3 then AgNO 3 Halide Ion
  13. 13. Results Table I -1 Br -1 White ppt dissolves White ppt Cl -1 Action of conc NH 3 on product Action of dilute NH 3 on product HNO 3 then AgNO 3 Halide Ion
  14. 14. Results Table I -1 Br -1 White ppt dissolves White ppt dissolves White ppt Cl -1 Action of conc NH 3 on product Action of dilute NH 3 on product HNO 3 then AgNO 3 Halide Ion
  15. 15. Results Table I -1 Cream ppt Br -1 White ppt dissolves White ppt Cl -1 Action of conc NH 3 on product Action of dilute NH 3 on product HNO 3 then AgNO 3 Halide Ion
  16. 16. Results Table I -1 Cream ppt Br -1 White ppt dissolves White ppt Cl -1 Action of conc NH 3 on product Action of dilute NH 3 on product HNO 3 then AgNO 3 Halide Ion
  17. 17. Results Table I -1 Cream ppt dissolves No reaction Cream ppt Br -1 White ppt dissolves White ppt Cl -1 Action of conc NH 3 on product Action of dilute NH 3 on product HNO 3 then AgNO 3 Halide Ion
  18. 18. Results Table insoluble Insoluble Yellow ppt I -1 Cream ppt dissolves Insoluble Cream ppt Br -1 White ppt dissolves White ppt Cl -1 Action of conc NH 3 on product Action of dilute NH 3 on product HNO 3 then AgNO 3 Halide Ion
  19. 19. Ionic Equations for the reaction <ul><li>Sodium chloride + Silver nitrate </li></ul><ul><li>NaCl + AgNO 3 </li></ul><ul><li>Repeat for Sodium Bromide and Silver iodide as above </li></ul>

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