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Intermolecular Force

Intermolecular Force. Chapter 11. Topics. I. Intermolecular Forces II. Properties of liquids III. Vapor Pressure IV. Phase change & phase diagrams. I. Intermolecular forces * Dipole-Dipole * Ion Dipole * London Dispersion Forces * H-bonding. Inter- vs. Intra-.

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Intermolecular Force

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  1. Intermolecular Force Chapter 11

  2. Topics • I. Intermolecular Forces • II. Properties of liquids • III. Vapor Pressure • IV. Phase change & phase diagrams

  3. I. Intermolecular forces* Dipole-Dipole* Ion Dipole* London Dispersion Forces * H-bonding

  4. Inter- vs. Intra- Intramural sports vs. Intercollegiate sports

  5. Generally, intermolecular forces are much weaker than intramolecular forces. Intermolecular Forces Intermolecular forces are attractive forces between molecules. NOT REAL BONDS! 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) • More Intermolecular forces in a solid than a liquid or gas “Measure” of intermolecular force boiling point melting point 11.2

  6. Orientation of Polar Molecules in a Solid Types of Intermolecular Forces 1. Dipole-Dipole Forces Attractive forces between polar molecules 11.2

  7. Ion-Dipole Interaction Types of Intermolecular Forces 2. Ion-Dipole Forces Attractive forces between an ion and a polar molecule 11.2

  8. 11.2

  9. Types of Intermolecular Forces 3. London Dispersion Forces – van der Walls forces (weakest) 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

  10. Dispersion forces usually increase with molar mass. Intermolecular Forces 3. Dispersion Forces Continued Polarizability is the ease with which the electron distribution in the atom or molecule can be distorted. • Polarizability increases with: • greater number of electrons • more diffuse electron cloud 11.2

  11. or … … H H B A A A Types of Intermolecular Forces 4. Hydrogen Bond (strongest) The hydrogen bond is a special dipole-dipole interaction between the hydrogen atom in a polar N-H, O-H, or F-H bond and an electronegative O, N, or F atom. A & B are N, O, or F 11.2

  12. Hydrogen Bond 11.2

  13. Why is the hydrogen bond considered a “special” dipole-dipole interaction? 11.2

  14. O O S 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. SO2 SO2 is a polar molecule: dipole-dipole forces. There are also dispersion forces between SO2 molecules. 11.2

  15. II. Properties of liquids

  16. Properties of Liquids Surface tension is the amount of energy required to stretch or increase the surface of a liquid by a unit area. There is an imbalance of Intermolecular forces High surface tension = lots of Intermolecular forces 11.3

  17. Demos • Paper clip • Wax paper

  18. Adhesion Properties of Liquids Cohesion is the intermolecular attraction between like molecules Adhesion is an attraction between unlike molecules (usually alludes to a molecule and a SURFACE) attracted to glass Cohesion attracted to each other 11.3

  19. Demos • Wet rope • Overnight buckets • Candle w/ dimes

  20. Properties of Liquids Viscosity is a measure of a fluid’s resistance to flow. Strong intermolecular forces High viscosity 11.3

  21. Properties of Liquids Capillary action is the rise of liquids up narrow tubes. (due to increased adhesive forces) • Demos • Towel in bucket • Capillary tube • Filter paper 11.3

  22. Maximum Density 40C Ice is less dense than water Water is a Unique Substance Density of Water 11.3

  23. III. Vapor Pressure

  24. Chemistry In Action: High-Temperature Superconductors

  25. Least Order Greatest Order T2 > T1 Condensation Evaporation 11.8

  26. H2O (l) H2O (g) Dynamic Equilibrium Rate of evaporation Rate of condensation = The equilibrium vapor pressure is the vapor pressure measured when a dynamic equilibrium exists between condensation and evaporation 11.8

  27. Clausius-Clapeyron Equation ln P = - DHvap + C RT Molar heat of vaporization (DHvap) is the energy required to vaporize 1 mole of a liquid. C = constant (depends on P & T) P = (equilibrium) vapor pressure T = temperature (K) R = gas constant (8.314 J/K•mol) 11.8

  28. The boiling point is the temperature at which the (equilibrium) vapor pressure of a liquid is equal to the external pressure. The normal boiling point is the temperature at which a liquid boils when the external pressure is 1 atm. 11.8

  29. The critical temperature (Tc) is the temperature above which the gas cannot be made to liquefy, no matter how great the applied pressure. The critical pressure (Pc) is the minimum pressure that must be applied to bring about liquefaction at the critical temperature. 11.8

  30. H2O (s) H2O (l) The melting point of a solid or the freezing point of a liquid is the temperature at which the solid and liquid phases coexist in equilibrium Freezing Melting 11.8

  31. Molar heat of fusion (DHfus) is the energy required to melt 1 mole of a solid substance. 11.8

  32. 11.8

  33. H2O (s) H2O (g) Molar heat of sublimation (DHsub) is the energy required to sublime 1 mole of a solid. Sublimation Deposition DHsub = DHfus + DHvap ( Hess’s Law) 11.8

  34. A phase diagram summarizes the conditions at which a substance exists as a solid, liquid, or gas. The triple point is where all 3 phases meet. Phase Diagram of Water 11.9

  35. 11.9

  36. Can you find… The Triple Point? Critical pressure? Critical temperature? Where fusion occurs? Where vaporization occurs? Melting point (at 1 atm)? Boiling point(at 6 atm)? Where’s Waldo? Carbon Dioxide

  37. 11.9

  38. Chemistry In Action: Liquid Crystals

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