Intermolecular forces


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Intermolecular forces

  1. 1. Intermolecular Forces and Liquids and Solids Chapter 11Copyright © 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 ion-induced dipole interaction dipole-induced dipole interaction 11.2
  8. 8. Induced Dipoles Interacting With Each Other 11.2
  9. 9. Intermolecular ForcesDispersion Forces ContinuedPolarizability is the ease with which the electron distributionin the atom or molecule can be distorted. Polarizability increases with: • greater number of electrons • more diffuse electron cloud Dispersion forces usually increase with molar mass. 11.2
  10. 10. 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
  11. 11. 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
  12. 12. Hydrogen Bond11.2
  13. 13. Why is the hydrogen bond considered a“special” dipole-dipole interaction? Decreasing molar mass Decreasing boiling point 11.2
  14. 14. Properties of LiquidsSurface tension is the amount of energy required to stretchor increase the surface of a liquid by a unit area. Strong intermolecular forces High surface tension 11.3
  15. 15. Properties of LiquidsCohesion is the intermolecular attraction between like moleculesAdhesion is an attraction between unlike molecules Adhesion Cohesion 11.3
  16. 16. Properties of LiquidsViscosity is a measure of a fluid’s resistance to flow. Strong intermolecular forces High viscosity 11.3
  17. 17. Water is a Unique Substance Maximum Density 40C Density of WaterIce is less dense than water 11.3
  18. 18. Types of CrystalsCovalent Crystals• Lattice points occupied by atoms• Held together by covalent bonds• Hard, high melting point• Poor conductor of heat and electricity carbon atoms diamond graphite 11.6
  19. 19. Types of CrystalsMetallic Crystals• Lattice points occupied by metal atoms• Held together by metallic bonds• Soft to hard, low to high melting point• Good conductors of heat and electricity Cross Section of a Metallic Crystal nucleus & inner shell e- mobile “sea” of e- 11.6
  20. 20. Crystal Structures of Metals 11.6
  21. 21. Types of Crystals 11.6
  22. 22. Chemistry In Action: High-Temperature Superconductors
  23. 23. Least Order Condensation Evaporation Greatest OrderT2 > T1 11.8
  24. 24. The equilibrium vapor pressure is the vapor pressuremeasured when a dynamic equilibrium exists betweencondensation and evaporation H2O (l) H2O (g) Dynamic Equilibrium Rate of Rate ofcondensation = evaporation 11.8
  25. 25. Before AtEvaporation Equilibrium 11.8
  26. 26. The boiling point is the temperature at which the(equilibrium) vapor pressure of a liquid is equal to theexternal pressure.The normal boiling point is the temperature at which a liquidboils when the external pressure is 1 atm. 11.8
  27. 27. H2O (s) H2O (l)The melting point of a solidor the freezing point of aliquid is the temperature atwhich the solid and liquid Freezing Meltingphases coexist in equilibrium 11.8
  28. 28. Molar heat of fusion (∆Hfus) is the energy required to melt1 mole of a solid substance at its freezing point. 11.8
  29. 29. Heating Curve 11.8