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AS Chemistry

AS Chemistry. Periodicity Period 3 - elements. Starter activity. Can you write one fact about each of the following elements? Na Mg Al Si P S Cl Ar. Learning Objectives. Candidates should be able to:

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AS Chemistry

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  1. AS Chemistry Periodicity Period 3 - elements

  2. Starter activity Can you write one fact about each of the following elements? • Na • Mg • Al • Si • P • S • Cl • Ar

  3. Learning Objectives Candidates should be able to: • describe qualitatively (and indicate the periodicity in) the variations in atomic radius, ionic radius, melting point and electrical conductivity of the elements (see the Data Booklet) • explain qualitatively the variation in atomic radius and ionic radius • interpret the variation in melting point and in electrical conductivity in terms of the presence of simple molecular, giant molecular or metallic bonding in the elements • explain the variation in first ionisation energy.

  4. Electronic configurations

  5. Atomic radius

  6. Atomic radius – what about argon? www.chemguide.co.uk/atoms/properties/atradius.html

  7. What is atomic radius?

  8. www.rjclarkson.demon.co.uk/found/period3_atomrad.gif

  9. Explaining the trend An atomic radius is a measure of the distance from the nucleus to the bonding pair of electrons. From sodium to chlorine, the bonding electrons are all in the 3rd shell being screened by the electrons in the first and second levels, i.e. the screening remains fairly constant. The increasing nuclear charge as you go across the period pulls the bonding electrons more tightly towards it.

  10. You have to ignore the noble gas at the end of each period. Because neon and argon don't form bonds, you can only measure their van der Waals radius - a case where the atom is pretty well "unsquashed". All the other atoms are being measured where their atomic radius is being lessened by strong attractions. You aren't comparing like with like if you include the noble gases. Leaving the noble gases out, atoms get smaller as you go across a period.

  11. IONIC RADIUS Ions aren't the same size as the atoms they come from. Compare the sizes of sodium and chloride ions with the sizes of sodium and chlorine atoms. • Positive ions • Positive ions are smaller than the atoms they come from. Sodium is 2,8,1; Na+ is 2,8. You've lost a whole layer of electrons, and the remaining 10 electrons are being pulled in by the full force of 11 protons. • Negative ions • Negative ions are bigger than the atoms they come from. Chlorine is 2,8,7; Cl- is 2,8,8. Although the electrons are still all in the 3-level, the extra repulsion produced by the incoming electron causes the atom to expand. There are still only 17 protons, but they are now having to hold 18 electrons.

  12. Electronegativity

  13. First ionisation energy

  14. Electronegativity

  15. Bonding, Structure and Properties

  16. Structure and Properties

  17. Electrical conductivity

  18. Melting and boiling points

  19. AS Chemistry Periodicity Period 3 - oxides

  20. Starter activity Complete these sketches to show how these properties change as you go along Period 3 from Na to Ar.

  21. Starter activity

  22. Starter activity

  23. Learning Objectives Candidates should be able to: • describe the reactions, if any, of the elements with oxygen to give Na2O, MgO, Al2O3, P4O10, SO2 and SO3. • state and explain the variation in oxidation number of the oxides. • describe the reactions of the oxides with water. • describe and explain the acid/base behaviour of oxides and hydroxides, including, where relevant, amphoteric behaviour in reaction with NaOH and acids.

  24. Reactions with oxygen

  25. Reactions with oxygen Sodium Sodium burns in oxygen with an orange flame to produce the white solid sodium oxide. Magnesium Magnesium burns in oxygen with an intense white flame to give white solid magnesium oxide.

  26. Aluminium Aluminium will burn in oxygen if it is powdered, otherwise the strong oxide layer on the aluminium tends to inhibit the reaction. If you sprinkle aluminium powder into a Bunsen flame, you get white sparkles. White aluminium oxide is formed. Silicon Silicon will burn in oxygen if heated strongly enough. Silicon dioxide is produced. Reactions with oxygen

  27. Reactions with oxygen Phosphorus White phosphorus catches fire spontaneously in air, burning with a white flame and producing clouds of white smoke - a mixture of phosphorus(III) oxide and phosphorus(V) oxide. The proportions of these depend on the amount of oxygen available. In an excess of oxygen, the product will be almost entirely phosphorus(V) oxide:

  28. Reactions with oxygen Sulphur Sulphur burns in air or oxygen on gentle heating with a pale blue flame. It produces colourless sulphur dioxide gas. In an excess of pure oxygen, some SO3 is also formed. This utilises the highest oxidation state of sulphur.

  29. Reactions with oxygen Which is which?

  30. Melting points of oxides Giant ionic and covalent solids contain only strong bonds and have high melting points. Simple molecules have weak vdW forces between molecules and have low melting points.

  31. Acid/base properties of the oxides

  32. Acid/base behaviour of aluminium oxide BASE: Al2O3 +3H2SO4→ Al2(SO4)3+3H2O ACID: Al2O3 +2NaOH+3H2O → 2NaAl(OH)4

  33. AS Chemistry Periodicity Period 3 - chlorides

  34. Learning Objectives Candidates should be able to: • describe the reactions, if any, of the elements with chlorine to give NaCl, MgCl2, Al2Cl6, SiCl4, and PCl5. • describe and explain the reactions of the chlorides with water.

  35. Reaction with chlorine

  36. Structure of Al2Cl6

  37. Acid/base properties of the chlorides

  38. AS Chemistry Periodicity Group 7 - Halogens

  39. Starter activity Can you complete task 1 – IGCSE revision on the halogens

  40. Learning Objectives Candidates should be able to: • describe the trends in volatility and colour of chlorine, bromine and iodine. • interpret the volatility of the elements in terms of van der Waals’ forces. • describe the relative reactivity of the elements as oxidising agents. • describe and explain the reactions of the elements with hydrogen. • describe and explain the relative thermal stabilities of the hydrides. • interpret these relative stabilities in terms of bond energies.

  41. The Halogens Ionic Covalent

  42. The Halogens Trend in colour and physical state

  43. Like dissolves like!

  44. AS Chemistry Periodicity Group 7 – the halides

  45. Starter activity Can you complete the table ‘Reducing power of the halides’?

  46. Trend in reducing ability

  47. Learning Objectives Candidates should be able to: • describe and explain the reactions of halide ions with • aqueous silver ions followed by aqueous ammonia • concentrated sulphuric acid. • describe and interpret in terms of changes of oxidation number the reaction of chlorine with cold, and with hot, aqueous sodium hydroxide. • explain the use of chlorine in water purification. • recognise the industrial importance and environmental significance of the halogens and their compounds, (e.g. for bleaches; PVC; halogenated hydrocarbons as solvents, refrigerants and in aerosols).

  48. Fluoride Chloride Bromide Iodide Relative reducing power Summary of reducing power

  49. Testing for halide ions Silver fluoride is soluble, and so you don't get a precipitate.

  50. Confirmatory tests E.g. AgCl(s)+ 2NH3(aq)→[Ag(NH3)2]+(aq) + Cl-(aq)

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