CHEM MOD 1

• Intermolecular forces (IMF, collectively known as van der Waals forces)

  Forces that exist between molecules and influence physical properties
• H2O in its three forms (ice, water, steam)

  • Bond angles are the same
  • Dipole moment is the same
  • Molecular shape is the same
  • Hybridization of the oxygen is the same

  
• Ice (solid H2O)


  Possesses a definite shape and volume, incompressible
• Liquid water


  Possesses a definite volume but will assume the shape of its container, slightly compressible
• Steam


  Assumes both the shape and volume of its container, extremely compressible
• Intermolecular forces (IMF)


  Cause real gases to deviate from ideal gas behavior
• Motion of molecules


  1. Gaseous phase: random and constant motion, each molecule moves independently

  2. Liquid: molecules slide past each other freely

  3. Solid: molecules vibrate about fixed positions
• London dispersion force


  Weakest of the intermolecular forces, between two nonpolar molecules, stronger the larger the atom or molecule
• Dipole-dipole interaction


  Occurs between two polar molecules, positively charged portion of one attracted to negatively charged portion of another
• Hydrogen bonding


  Electrostatic interaction between a hydrogen and a lone electronegative pair of atom, usually with fluorine, nitrogen or oxygen
• Ion-dipole interaction


  Occurs when an ion encounters a polar molecule, charge of ion determines attraction and repulsion
• Stronger intermolecular forces result in higher boiling points and melting points
• Stronger intermolecular forces result in lower vapor pressure and lower concentration of molecules in the gaseous state