Intermolecular Force

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Intermolecular Force

  1. 1. Intermolecular Forces and Liquids and SolidsCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  2. 2. A phase is a homogeneous part of the system incontact with other parts of the system butseparated from them by a well-defined boundary. 2 Phases Solid phase - ice Liquid phase - water 11.1
  3. 3. Intermolecular ForcesIntermolecular forces are attractive forces between molecules.Intramolecular forces hold atoms together in a molecule. Intermolecular vs Intramolecular • 41 kJ to vaporize 1 mole of water (inter) • 930 kJ to break all O-H bonds in 1 mole of water (intra) “Measure” of intermolecular force Generally, boiling point intermolecular forces are much melting point weaker than ∆Hvap intramolecular ∆Hfus forces. ∆Hsub 11.2
  4. 4. Intermolecular ForcesDipole-Dipole Forces Attractive forces between polar molecules Orientation of Polar Molecules in a Solid 11.2
  5. 5. Intermolecular ForcesIon-Dipole Forces Attractive forces between an ion and a polar molecule Ion-Dipole Interaction 11.2
  6. 6. 11.2
  7. 7. Intermolecular ForcesDispersion Forces Attractive forces that arise as a result of temporary dipoles induced in atoms or molecules 11.2
  8. 8. What type(s) of intermolecular forces exist between each of the following molecules?HBr HBr is a polar molecule: dipole-dipole forces. There are also dispersion forces between HBr molecules.CH4 CH4 is nonpolar: dispersion forces. S OSO2 O SO2 is a polar molecule: dipole-dipole forces. There are also dispersion forces between SO2 molecules. 11.2
  9. 9. Intermolecular ForcesHydrogen BondThe hydrogen bond is a special dipole-dipole interactionbetween they hydrogen atom in a polar N-H, O-H, or F-H bondand an electronegative O, N, or F atom. A H…B or A H…A A & B are N, O, or F 11.2
  10. 10. Hydrogen Bond11.2
  11. 11. Why is the hydrogen bond considered a“special” dipole-dipole interaction? Decreasing molar mass Decreasing boiling point 11.2
  12. 12. A crystalline solid possesses rigid and long-range order. In acrystalline solid, atoms, molecules or ions occupy specific(predictable) positions.An amorphous solid does not possess a well-definedarrangement and long-range molecular order.A unit cell is the basic repeating structural unit of a crystallinesolid. lattice At lattice points: point • Atoms • Molecules • IonsUnit Cell Unit cells in 3 dimensions 11.4
  13. 13. When silver crystallizes, it forms face-centered cubic cells. The unit cell edge length is 409 pm. Calculate the density of silver. m d= V = a3 = (409 pm)3 = 6.83 x 10-23 cm3 V 4 atoms/unit cell in a face-centered cubic cell 107.9 g 1 mole Agm = 4 Ag atoms x x = 7.17 x 10-22 g mole Ag 6.022 x 1023 atoms m 7.17 x 10-22 g d= = = 10.5 g/cm3 V 6.83 x 10-23 cm3 11.4
  14. 14. An amorphous solid does not possess a well-definedarrangement and long-range molecular order.A glass is an optically transparent fusion product of inorganicmaterials that has cooled to a rigid state without crystallizing Crystalline Non-crystalline quartz (SiO2) quartz glass 11.7
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