Intermolecular Forces of Attraction

• Intermolecular forces


  Attractive forces between molecules that are weaker than bonds
• Intermolecular forces


  • They influence the physical properties of molecular liquids and solids
  • They are generally weaker than ionic or covalent bonds
• London dispersion force


  Weak temporary intermolecular force that occurs between atoms or molecules (polar or nonpolar)
• London dispersion force


  • It results from momentary uneven electron distributions in molecules
  • The strength depends on the polarizability of the molecule
• Factors affecting dispersion force


  • Size of atom or molecule
  • Shape of molecules with similar masses
• Dipole-dipole interaction


  Intermolecular force that occurs between polar molecules
• Hydrogen bonding


  Special type of dipole-dipole interaction between hydrogen in a polar bond and a nearby electronegative atom
• Hydrogen bonding


  • It has a powerful effect on the structures and properties of many compounds
  • It is not a chemical bond
• Ion-dipole force


  Force between an ion and the partial charge on the end of a polar molecule
• Types of intermolecular forces

  • Dispersion forces
  • Dipole-dipole forces
  • Hydrogen bonds
  • Ion-dipole forces
• The effects of all intermolecular attractions are additive
• Viscosity


  Measure of a fluid's resistance to flow
• Viscosity of liquids

  Decreases with increasing temperature
• Surface tension


  Energy required to increase the surface area of a liquid by a unit amount
• Surface tension


  • It is caused by an imbalance of intermolecular forces at the surface of the liquid
  • It is higher for liquids with stronger intermolecular forces like hydrogen bonding
• Capillary action


  Rise of liquids up a very narrow tube due to cohesion and adhesion
• Capillary action helps water and dissolved nutrients move upward through plants