IMF

• Solid


  • Little free space between particles
  • Strong intermolecular force between molecules
  • Particles fixed in place but vibrate around a fixed position
  • Regular arrangement of particles
• Liquid


  • Some free space between particles
  • Intermolecular forces strong enough to hold molecules close together
  • Particles move past one another
  • Short range order arrangement of particles only repeats itself for a small number of particles
• Gas


  • Particles are widely separated
  • Lack significant attractive force between molecules
  • Particles move through space
  • No orderly arrangement
• Intermolecular Forces (IMF)

  • London dispersion force
  • Dipole-dipole force
  • Hydrogen-bonding force
• London dispersion force


  • Occurs between ALL atoms and molecules
  • The only IMF at work in nonpolar substances
  • The only type of IMF operating between nonpolar molecules
• Dipole-dipole force


  • The partially positively charged part of a POLAR molecule gets electrostatically attracted with the partially negatively charged part of a neighboring POLAR molecule, causing the molecules to align
  • Stronger than London dispersion forces
  • Occur between molecules that have permanent net dipoles (POLAR molecules)
• Hydrogen-bonding force


  • Occurs between molecules that have a permanent net dipole resulting from hydrogen being covalently bonded to either fluorine, oxygen or nitrogen
  • The STRONGEST IMF because the hydrogen nucleus (extremely small and positively charged) and F, N, O and are very electronegative, that the hydrogen atom gets strongly attracted to the F, N, O atoms
• As the intermolecular attraction increases

  The vapor pressure (the pressure of the vapor that is in equilibrium with its liquid) decreases
• As the intermolecular forces increase

  The viscosity increases
• As temperature increases

  The viscosity decreases
• Surface Tension

  • Measure of the elastic force in the surface of a liquid
  • Amount of energy required to stretch or increase the surface of a liquid by unit area
  • Somewhat decreases as temperature increases
• Adhesion

  Two different substances
• Cohesion


  Same substances
• Capillary action happens by means of surface tension
• Concave meniscus indicates high viscosity, convex meniscus indicates low viscosity
• Surfactant


  Materials used to decrease surface tension
• Density


  • Related to the distance between particles
  • Generally, liquids are denser than gases, and nearly as dense as solids
• Viscosity


  • Measure of a fluid's resistance to flow
  • The greater the viscosity, the more slowly the liquid flows
  • Higher IMF, greater viscosity
  • Viscosity decreases as temperature increases
• Vapor pressure


  • Partial pressure exerted by gas molecules above a liquid when the two states are in equilibrium
  • Dependent upon the IMF of a liquid and the temperature of the system
  • Vapor pressure decreases when IMF increase