Intermolecular Forces

• Gas


  • Has an indefinite shape and volume
  • Low density
  • Very compressible
  • Very free motion
• Liquid


  • Has an indefinite shape but definite volume
  • High density
  • Only slightly compressible
  • Slide past one another freely
• Solid


  • Has a definite shape and volume
  • High density
  • Virtually incompressible
  • Vibrate about fixed position
• Phase of matter


  Distinct form of matter that has uniform physical and chemical properties throughout
• Intermolecular Forces (IMF)


  Attractive or repulsive forces between molecules
• Chemical Bonding


  • Holds atoms together in a molecule
  • Attractive force within molecules (or atoms)
• Intermolecular Forces


  Attractive force between molecules
• Chemical Bonding vs Intermolecular Forces


  Chemical Bonding is stronger and more likely permanent, Intermolecular Forces are weaker and temporary
• Types of Intermolecular Forces

  • Ion-Ion Forces
  • Ion-dipole Forces
  • Dipole-dipole Forces
  • Hydrogen Bond Forces
  • London Forces
• Ion-Ion Forces


  • Occurs between ionic compounds/solids
  • The strongest IMF because they involve formal charges
  • Electrostatic force between oppositely charged ions
• Ionic compounds with Ion-Ion Forces


  • NaCl (Sodium Chloride)
  • CaO (Calcium Oxide)
  • MgSO4 (Magnesium Sulfate)
• Dipole


  A molecule (covalent) that has a pair of equal and opposite charges (+ and -)
• Ion-dipole Forces


  • Occurs between ionic compounds and polar covalent compounds
  • Involves ions and polar molecules (polar solvents)
• Compounds with Ion-dipole Forces

  • NaCl and H2O (Sodium Chloride and Water)
  • KCl and H2O (Potassium Chloride and Water)
  • NH4Cl and H2O (Ammonium Chloride and Water)
• Dipole-dipole Forces


  • Occurs between polar covalent compounds
  • Involves polar molecules that are usually permanent dipole molecules
• Compounds with Dipole-dipole Forces

  • CO (Carbon Monoxide)
  • HBr (Hydrogen Bromide)
  • SO2 (Sulfur Dioxide)
• Hydrogen Bond Forces


  • Special type of dipole-dipole forces
  • Occurs between polar covalent compounds, particularly between compounds with H and compounds with N, O, or F
• Compounds with Hydrogen Bond Forces

  • H2O (Water)
  • HF (Hydrogen Fluoride)
  • C2H5OH (Ethanol)
  • CH3OH (Methanol)
• London Forces


  • Also known as dispersion forces or Van Der Waals forces
  • Weakest IMF
  • Occurs between any type of substance or compound, but mostly between nonpolar covalent compounds and monoatomic species
• Compounds with London Forces


  • N2 (Nitrogen gas)
  • He (Helium)
  • CO2 (Carbon dioxide)
• Electronegativity Differences


  Determines the type of covalent bond (nonpolar, polar, ionic)
• Net Dipole Moment


  Measure of the overall polarity of a molecule
• Molecular geometry is always more accurate than electronegativity differences in determining the type of covalent bond
• How to differentiate the types of IMF

  • Ion-Ion Forces: formal charges
  • Ion-dipole Forces: formal charge and partial charge
  • Dipole-dipole Forces: partial charges
  • Hydrogen Bond Forces: partial charges
  • London Forces: induced dipoles
• Electronegativity differences


  • Molecular Geometry (presence and absence of net dipole moment) is more accurate than electronegativity differences
• Electronegativity Differences and Bond Type

  • Nonpolar covalent (<0.4)
  • Polar covalent (Between 0.5 and 1.9)
  • Ionic (>2.0)
• Net Dipole Moment


  Measure of the overall polarity of a molecule. It occurs when a molecule has polar bonds and the individual bond polarities don't cancel each other out due to the molecule's shape or symmetry.
• Direction of dipole moments and Net Dipole Moment

  • Opposite, Not present - Nonpolar
  • Not opposite/parallel, Present - Polar
• Types of Intermolecular Forces (IMF)

  • Ion-Ion Forces
  • Ion-dipole Forces
  • Dipole-dipole Forces
  • Hydrogen Bond Forces
  • London Forces
• Ion-Ion Forces


  Formal charges
• Ion-dipole Forces


  Formal charge and partial charge
• Dipole-dipole Forces


  Partial charges
• Hydrogen Bond Forces


  Partial charges
• London Forces


  Induced dipoles
• Ranking of IMF from weakest to strongest

  • London Forces
  • Dipole-dipole Forces
  • Ion-dipole Forces
  • Hydrogen Bond Forces
  • Ion-Ion Forces
• Applications of Intermolecular Forces

  • Solubility Processes
  • Drug Design and Pharmaceuticals
  • Food Science and Cooking
  • Environmental Science
• Solubility Processes


  IMF helps in predicting the solubility of substances in different solvents. Polar solvents like water dissolve polar solutes due to dipole-dipole and hydrogen bonding interactions. Nonpolar solvents dissolve nonpolar substances due to London forces.
• Solubility Examples


  • H2O (water) - Polar solvent, Type of IMF present: dipole-dipole/hydrogen bond forces
  • C11H12O11 (table sugar) - Polar solute
  • C6H6 (Benzene) - Nonpolar solvent, Type of IMF present: London forces
  • CHCl3 (Chloroform) - Nonpolar solute
• Drug Design and Pharmaceuticals

  Pharmaceutical scientists design drugs that can interact with specific receptors through hydrogen bonding, dipole-dipole interactions, or other types of IMF. Solubility and bioavailability of drugs are influenced by their intermolecular interactions with body fluids and tissues.
• Drug Design and Pharmaceuticals Examples

  • C4H5N3O (Cytosine) - Nonpolar solvent, Type of IMF present: Hydrogen bond forces
  • C8H11N5O3 (Acyclovir) - Antiviral drug