Intermolecular Forces

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Intermolecular Forces

• Hold molecules to each other
• (Not covalent or ionic)
• Three types

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London Forces

• vander Waals or Induced Dipole
• All molecules
• Short-lived

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London Forces

• Increase with increasing molecular weight

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London Forces

• Increase with more spread out molecules
• 2,2-dimethylpropane, bp 9.5ºC
• pentane, bp 35ºC

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Dipole-Dipole Forces

• Polar molecules permanent dipole
• Positive and negative ends attract
• Butane, MW58.0 g/mol, bp -0.5ºC
• Acetone, MW58.0 g/mol, bp 56.2ºC

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Hydrogen Bonding

• Hydrogen bonded to highly electronegative element
• Fluorine, Oxygen and Nitrogen (FON)
• Structures of Ammonia and Water
• Boiling points

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Density of Water

• 1.00 g/mL at 4C
• Decreases as temperature increases or decreases
• Ice is less dense than water

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Vapor Pressure and Boiling Point

• Vapor Pressure

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• Boiling point is the temperature at which the
  vapor pressure is equal to atmospheric pressure.
• Normal boiling point is the temperature at which
  the vapor pressure is equal to 760 mm Hg

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• Boiling Point
• Intermolecular Forces
• Molecular Shape

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Solids

• Crystalline solids
• Amorphous solids
• See display case behind SB168

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Phase Changes

• Heat of Fusion amount of heat energy (cal)
  required to change a substance from the solid to
  the liquid form
• Heat of Vaporization - amount of heat energy
  (cal) required to change a substance from the
  liquid to the gas form