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Unless otherwise stated, all images in this file have been reproduced from: Blackman, Bottle, Schmid, Mocerino and Wille, Chemistry , 2007 (John Wiley)      ISBN: 9 78047081 0866 . CHEM1002 [Part 2]. Dr Michela Simone Weeks 8 – 13 Office Hours: Monday 3-5, Friday 4-5

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  1. Unless otherwise stated, all images in this file have been reproduced from: Blackman, Bottle, Schmid, Mocerino and Wille,Chemistry, 2007 (John Wiley)     ISBN: 9 78047081 0866

  2. CHEM1002 [Part 2] Dr Michela Simone Weeks 8 – 13 Office Hours: Monday 3-5, Friday 4-5 Room: 412A (or 416) Phone: 93512830 e-mail:michela.simone@sydney.edu.au

  3. Summary of Last Lecture • Crystal structures I • Hexagonal close packing arises when close packed layers repeat every third layer (ABABABAB) • Cubic close packing arises when close packed layers repeat every fourth layer (ABCABCABC) • The coordination number in both types of close packing is 12 • Unit cells are the simplest building blocks from which the whole solid can be built • Atoms on corners of unit cells are shared between 8 cells, atoms on faces of unit cells are shared between 2 cells, atoms on edges of unit cells are shared between 4 cells and atoms at the centres of unit cells are unshared.

  4. Crystal Structures II • Lecture 9: • Packing efficiency • Octahedral and tetrahedral interstitial holes • Ionic crystal structures • Blackman Chapter 7, Section 7.4 (pages 265-268) • Next week’s lectures • Lectures 10 and 11: solubility • Blackman Chapter 10, Sections 10.1 – 10.4 • Revise equilibrium calculations from CHEM1001! • Lecture 12: introduction to coordination chemistry • Blackman Chapter 13, Sections 13.1 – 13.4

  5. Packing Efficiency I: Atoms in Cell • The unit cell for CCP is face centred cubic (FCC) • atoms on each corner and atoms on each face of the cube • Atoms on corners: • Atoms on faces: • Total:

  6. Packing Efficiency II: Volume Occupied by Atoms • The unit cell for CCP is face centred cubic (FCC) • atoms on each corner and atoms on each face of the cube • If each atom has radius r, • volume of atom = • Number of atoms = • Volume occupied by atoms =

  7. Packing Efficiency III: Volume of Unit Cell • The unit cell for CCP is face centred cubic (FCC) • atoms on each corner and atoms on each face of the cube • Close packed direction is diagonal of face a • Length of diagonal: r a r • Length of side: r r • Volume of cubic unit cell:

  8. Packing Efficiency IV: FCC • The unit cell for CCP is face centred cubic (FCC) • atoms on each corner and atoms on each face of the cube • Volume occupied by atoms • Volume of unit cell • Packing efficiency

  9. Cubic Close Packing: CCP and HCP • Cubic close packing: • Layers repeat ABCABCABC • Number of atoms in unit cell = 4 • Packing efficiency = 74% • Coordination number = 12 • Hexagonal close packing • Layers repeat ABABAB • Packing efficiency = 74% • Coordination number = 12

  10. Other Metal Structures • Simple cubic • Number of atoms in unit cell = 1 • Packing efficiency = 52% • Coordination number = 6 • Body centred cubic • Number of atoms in unit cell = 2 • Packing efficiency = 68% • Coordination number = 8

  11. Interstitial Holes - Oh • Even in the close packed structures, there are spaces for extra atoms • Octahedral interstitial holes • at the centre of the cube and on each edge

  12. Interstitial Holes - Td • Even in the close packed structures, there are spaces for extra atoms • Tetrahedral interstitial holes • in the centre of the cube corners

  13. Common Structures • For every n close packed atoms, there are • n octahedral holes and • 2n tetrahedral holes • Almost all of the common structures can be thought as of being derived from • Close packed (CCP or HCP) anions • Cations in octahedral and/or tetrahedral interstitials

  14. Common Structures - Rocksalt • NaCl (rocksalt) • CCP Cl- anions with Na+ in all of the octahedral interstitials

  15. Common Structures - Zinc Blende • Zinc Blende (ZnS) • CCP S2- anions with Zn2+ in half of the tetrahedral interstitials

  16. Common Structures - Anti-Fluorite • Anti-Fluorite (Na2O) • CCP O2- anions with Na+ in all of the tetrahedral interstitials

  17. Common Structures - Fluorite • Fluorite (CaF2) • CCP Ca2+ cations with F- in all of the tetrahedral interstitials

  18. Common Structures

  19. Summary: Crystal Structures II • Learning Outcomes - you should now be able to: • Complete the worksheet • Work out the number of atoms in a unit cell • Understand the calculation of packing efficiency • Recall the packing efficiency and coordination numbers of HCP, CCP, BCP and simple cubic structures • Be able to rationalize ionic structures in terms of filling of interstitial holes • Next lecture: • Solubility

  20. Practice Examples • How many atoms are there in the body-centred cubic unit cell of tungsten? • # atoms = 1 • # atoms = 1 + 1/8 × (8) = 2 • # atoms = 1/2 × (6) = 3 • # atoms = 1/2 × (6) + 1/8 × (8) = 4 • # atoms = 1 + 1/2 × (6) + 1/8 × (8) = 5 • Verify that the efficiency of simple cubic packing is 52% and BCP is 68%.

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