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AS Chemistry
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AS Chemistry

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  1. AS Chemistry Covalent bonding

  2. Learning Objectives • Candidates should be able to: • describe, including the use of ‘dot-and-cross’ diagrams, covalent bonding, as in hydrogen; oxygen; chlorine; hydrogen chloride; carbon dioxide; methane; ethene. • describe covalent bonding in terms of orbital overlap.

  3. Starter Activity

  4. Forming a bond

  5. Shared pair of electrons

  6. Electron density map Electron density maps for a hydrogen molecule

  7. Representing a covalent bond This single σcovalent bond can be simply represented as: or H – H

  8. Overlap of atomic orbitals Overlap of two p-orbitals – e.g. F2 Overlap of one s and one p orbital – e.g. HF

  9. Dot-cross diagrams Oxygen Chlorine Methane Carbon dioxide Hydrogen chloride Ethene

  10. Breaking the octet rule Unexpected structures !!

  11. Bonding in CH4– promotion of an electron C 1s2 2s2 2p2

  12. Bonding in CH4– hybridisation

  13. Hybridisation in PCl5

  14. AS Chemistry Co-ordinate bonding

  15. Learning Objectives Candidates should be able to describe, including the use of ‘dot-and-cross diagrams, co-ordinate (dative covalent) bonding, as in the formation of the ammonium ion and in the Al2Cl6 molecule. A co-ordinate bond (also called a dative covalent bond) is a covalent bond (a shared pair of electrons) in which both electrons come from the same atom.

  16. Starter Activity

  17. Dot-cross diagrams H2S SiCl4 SF6 CH3OH CO

  18. Reaction between NH3(g) and HCl(g)

  19. Reaction between NH3(g) and HCl(g)

  20. Reaction between H2Oand HCl

  21. Electron-deficient BF3

  22. Aluminium chloride vapour

  23. Aluminium chloride vapour

  24. AS Chemistry Electronegativity

  25. Learning Objectives Candidates should be able to explain the origin of polar bonds, with reference to electronegativity differences between atoms. Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons.

  26. Electronegativity values

  27. Starter Activity

  28. Why are bonds like bears? …’cos some of them are POLAR!

  29. Electronegativity differences What happens if two atoms of equal electronegativity bond together? What happens if B is slightly more electronegative than A?

  30. Representing polar bonds

  31. Representing polar bonds

  32. Large electronegativity difference What happens if B is a lot more electronegative than A? An ionic bond is formed!!!

  33. Type of bond As a rough guide:

  34. Ionic with increasing covalent character

  35. Polarisation of Anions Truly ionic Positive cationNegative anion Ionic with some covalent character

  36. Polarisation of Anions High High Small Large

  37. Do polar bonds make polar molecules? CCl4 molecule is tetrahedral - the partial negative charges on the Cl atoms are distributed pretty symmetrically around the molecule. The partial positive charge on the C is buried in the center of the molecule.

  38. The most electronegative element is fluorine. If you remember that fact, everything becomes easy, because electronegativity must always increase towards fluorine in the Periodic Table.

  39. Trends in electronegativity

  40. AS Chemistry Ionic bonding

  41. Learning Objectives Candidates should be able to describe ionic (electrovalent) bonding, as in sodium chloride and magnesium oxide, including the use of ‘dot-and-cross’ diagrams.

  42. “The name’s Bond, Ionic Bond – taken, not shared!!!

  43. Starter Activity

  44. Approaching atoms

  45. Ionic bonding

  46. Ionic bonding MgO CaCl2 K2O Al2O3

  47. Why CaCl2 and not CaCl or CaCl3?

  48. Why CaCl2 and not CaCl or CaCl3?

  49. Polarisation of Anions Truly ionic Positive cationNegative anion Ionic with some covalent character