Chapter 12 - CHE 1301 Petrucci Harwood Herring Madura...

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Click to edit Master subtitle style 11 CHE 1301 Petrucci, Harwood, Herring, Madura Chapter 12: Liquids, Solids, and Intermolecular Forces Dr. Bruce E. Hodson
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22 12.0 Introduction: Inter- and Intra- molecular forces
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33 Inter molecular forces are of little significance; why? Inter molecular forces must be considered Inter molecular forces are very important 12.0 Inter molecular forces and States It’s essentially all about FREEDOM of motion
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44 Molecules and atoms are in constant random motion, which increases with increasing temperature ( THERMAL ENERGY ) 12.0 Inter molecular forces and States
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55 12.0 Introduction ….. when thermal energy is high relative to intermolecular forces, matter tends to be gaseous When thermal energy is low relative to intermolecular forces, matter tends to be liquid or solid ……..
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66 12.0 Introduction: Pressure and States Note that we can also change states by changing pressure
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77 Intermolecular forces are generally much weaker than bonding forces 12.0 Intermolecular Forces: Origins and Strength Intermolecular forces originate from the interactions between charges , partial charges and temporary charges on atoms or ions larger the charge = stronger attraction longer the distance = weaker attraction Boil: 100°C Decompose: 1000s of °C
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88 Intermolecular Forces : The Forces that hold Condensed States Together Four General Types
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99 12.5 Van der Waals (a.k.a. London, or Dispersion ) Forces Fluctuations in the electron distribution in atoms and molecules result in a temporary dipole ( happens in ALL compounds ) He
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1010 12.5 Van der Waals (a.k.a. London, or Dispersion ) Forces An temporary (instantaneous) dipole on any one He atom induces temporary dipoles on neighboring atoms, which then attract one another He V. d. W. forces are weak ( 298 K He(g) ), but significant at lower T ( 4 K He(l) ) Dipole – Induced Dipole Interaction
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1111 12.5 Van der Waals (a.k.a. London, or Dispersion) Forces Magnitude of dispersion force depends on ability to polarize (property: polarizability ) in response to an instantaneous dipole More electrons (higher molar mass) = higher polarizability = stronger dispersion forces
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1212 12.5 Van der Waals (a.k.a. London, or Dispersion) Forces Molar mass is not the only factor: Weaker dispersion forces
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1313 12.5 Van der Waals (a.k.a. London, or Dispersion) Forces Shape is important, but molar mass gives a general guide
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1414 12.5 Dipole-Dipole Interactions
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1515 12.5 Dipole-Dipole Interactions Polar substances have higher Mp and Bp than non-polar substances of similar molar mass (note: dispersion forces still present !!) Dipole-dipole forces exist in all polar molecules (they have permanent dipoles)
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