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Intramolecular Forces

Intramolecular Forces. Forces (chemical bonds) within a molecule Typical value: 350 kJ/mol C-C bond. Intermolecular Forces. Forces between molecules Typical value: 20 kJ/mol H-bond 1 kJ/mol van der Waals. Dipole-dipole Forces If present usually dominate intermolecular

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Intramolecular Forces

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  1. Intramolecular Forces Forces (chemical bonds) within a molecule Typical value: 350 kJ/mol C-C bond Intermolecular Forces Forces between molecules Typical value: 20 kJ/mol H-bond 1 kJ/mol van der Waals

  2. Dipole-dipole Forces If present usually dominate intermolecular interactions.

  3. Water Held together by O-H•••H hydrogen bonds

  4. Hydrogen bond donors: O-H, N-H, S-H, X-H Hydrogen bond acceptors: O, N, X, S For example: The amide hyrdrogen bond is the dominate intermolecular force in proteins.

  5. London Dispersion Forces or van der Waals Forces

  6. What determines the B.P. of a liquid? DGvap = DHvap - T DSvap = 0 at the B.P. DHvap = T DSvap For simple liquids, all Dsvap values are about the same. So B.P. is proportional to DHvap

  7. Four General Classifications for Solids 1. Metals Fe, Co, Ag 2. Covalent Network Solids Diamond, SiO2 3. Ionic Solids NaCl ZnS 4. Molecular Solids I2 Sugar

  8. Bragg’s Law

  9. Determination of Crystal Structures using X-Ray diffraction. Diffraction of any wave will take place when you have a grid with a spacing similar to the wavelength of the wave. X-Rays have wavelengths on the order of 1 Ångstrom. Typical value 0.71Å

  10. Four General Classifications for Solids 1. Metals Fe, Co, Ag 2. Covalent Network Solids Diamond, SiO2 3. Ionic Solids NaCl ZnS 4. Molecular Solids I2 Sugar

  11. Close Packing of Spheres

  12. Hexagonal Close Packed Co, Ti, Mg

  13. Body Centered Cubic Fe, Cr, V

  14. Cubic Close Packed - Face Centered Cubic Ni, Cu, Au

  15. Efficiency of Close Packing What fraction of the volume is occupied? fv = volume spheres in unit cell / volume of cell = 0.740 fv =

  16. The radius of Ag atom is 1.44 Å. Calculate the density. The Ag structure is fcc (ccp).

  17. The radius of Ag atom is 1.44 Å. Calculate the density. The Ag structure is fcc (ccp). =

  18. Close packing of spheres fills 0.74 % of the available space The remaining space can be allotted to three types of holes that occur between the spheres.

  19. rtet = 0.225 roct = 0.414 rcub = 0.732

  20. Sodium Chloride Na+ .95 Å Cl- 1.81Å Table 13.7 Ratio = .95 / 1.81 = .52 rtet = 0.225 roct = 0.414 rcub = 0.732

  21. Zinc Sulfide Ratio = Zn+2/S-2 = .35 rtet = 0.225 roct = 0.414 rcub = 0.732 The Zinc atoms occupy 1/2 of the tetrahedral holes

  22. Glass Quartz

  23. Molecular Solids C60

  24. Iodine I2

  25. Acetylene HCCH

  26. Oxalic Acid

  27. P DG = DH - TDS = - RT ln K ln K = -(DH/R) /T + DS/R ln P = -(DH/R)(1/T) + DS/R

  28. Triple point 4.588 torr 0.0098°C

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