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Revision part3

Revision part3 . Periodicity. Aims. Electronegativity Ionisation energies Atomic radii Boiling points Group 2 redox reactions Group 2 oxides with water Thermal decomposition Group 7 properties Displacement reaction of grp 7 Testing for halide ions Uses of Cl. Electronegativity.

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Revision part3

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  1. Revision part3 Periodicity

  2. Aims • Electronegativity • Ionisation energies • Atomic radii • Boiling points • Group 2 redox reactions • Group 2 oxides with water • Thermal decomposition • Group 7 properties • Displacement reaction of grp 7 • Testing for halide ions • Uses of Cl

  3. Electronegativity • A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond • On your periodic table draw this trend

  4. Ionisation energies • 1st IE the energy required to remove on electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions. 3 factors that influence IE • The distance of the outermost electron from the nucleus (atomic radius) • Electron shielding • Nuclear charge

  5. Atomic radii Number of protons increases; shielding stays the same Radius decreases Extra shells and more shielding outweigh additional protons in the nucleus Radius increases

  6. Boiling points: they are related to structure

  7. Group 2 redox reactions • Identify what is being oxidised and what is being reduced • Mg + O2 2MgO O has gained electrons Oxidation numbers 0 0 +2 -2 Mg has lost electrons

  8. Group 2 with oxygen Reactivity increases down the group. This is explained by the increasing ease with which group 2 elements form the corresponding 2+ ion. Mg + ½ O2 MgO burns with a bright white flame Ca + ½ O2  CaO burns with a brick-red colour Sr + ½ O2  SrO burns with a crimson colour Ba + ½ O2  BaO burns with a green colour

  9. Group 2 with water • Group 2 elements also undergo a redox reaction with water Oxidation numbers 0 +1 -2 +2 -2+1 0 Mg + 2H2O Mg(OH)2 + H2 The rate of reaction increases down the group, largely due to the ease of cation formation

  10. Group 2 oxides with water All group 2 metal oxides react with water to form hydroxides: MgO + H2O  Mg(OH)2 They are not redox reactions. The oxidation numbers stay the same Ca(OH)2 neutralize soil and lakes Mg(OH)2 antacids

  11. Thermal decomposition of group 2 carbonates Group 2 carbonates decompose to form oxides and carbon dioxide MgCO3 MgO + CO2 The ease at which a carbonate decomposes decreases down a group Again they are not redox reactions

  12. GROUP TRENDS APPEARANCE F2 Cl2 Br2 I2 Colour Yellow Green Red/brown Grey State (at RTP) GAS GAS LIQUID SOLID BOILING POINT F2 Cl2 Br2 I2 Boiling point / °C - 188 - 34 58 183 INCREASES down Group • increased size makes the van der Waals forces increase • more energy is required to separate the molecules

  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 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)

  14. HALOGENS - DISPLACEMENT REACTIONS DISPLACEMENT REACTIONS - EXPERIMENT SODIUM CHLORIDE SODIUM BROMIDE SODIUM IODIDE CHLORINE Solution stays colourless NO REACTION Solution goes from colourless to orange-yellow BROMINE FORMED Solution goes from colourless to orange-red IODINE FORMED BROMINE Solution goes from colourless to orange-yellow NO REACTION Solution goes from colourless to orange-yellow NO REACTION Solution goes from colourless to red IODINE FORMED

  15. OTHER REACTIONS OF CHLORINE Water Halogens react with decreasing vigour down the group as their oxidising power decreases Litmus will be turned red then decolourised in chlorine water Cl2(g) + H2O(l)HCl(aq) + HOCl(aq) strong acid bleaches by oxidation This is an example of DISPROPORTIONATION … ‘simultaneous oxidation and reduction of a species’ Alkalis Chlorine reacts with cold, aqueous sodium hydroxide. 2NaOH(aq) + Cl2(g) —> NaCl(aq) + NaOCl(aq) + H2O(l) 0 -1 +1

  16. 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 colourlessdiammine complex is formed [Ag(NH3)2]+(aq)

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

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

  19. TESTING FOR HALIDES – AgNO3 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

  20. TESTING FOR HALIDES – AgNO3 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

  21. HALOGENS & HALIDES - USES Chlorine, Cl2 • water purification • bleach • solvents • polymers - poly(chloroethene) or PVC • CFC’s Fluorine, F2 • CFC’s • polymers - PTFE poly(tetrafluoroethene) as used in... non-stick frying pans, electrical insulation, waterproof clothing Fluoride, F¯ • helps prevent tooth decay - tin fluoride is added to toothpaste - sodium fluoride is added to water supplies Hydrogen fluoride, HF • used to etch glass Silver bromide, AgBr • used in photographic film

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