Intermolecular Forces

• Intramolecular forces


  Forces that hold molecules together, forces within a molecule
• Intermolecular forces


  Forces that form between molecules, atoms, or ions
• Intramolecular forces are many times stronger than intermolecular forces of attraction
• Four main types of intermolecular forces

  • Ion-ion interaction
  • Dipole-dipole interaction
  • Hydrogen bonding
  • Dispersion forces (London forces)
• Ion-ion interaction


  • Exists between oppositely charged ions, occurs in ionic compounds, most ion-ion interaction is strong, strength is inversely proportional to square of distance between ions
• Dipole-dipole interaction


  • Occurs between polar molecules, average dipole-dipole interaction is relatively weak, strength is inversely proportional to distance raised to the fourth power
• Hydrogen bonding


  • Very strong dipole-dipole interaction, occurs in polar molecules containing H and highly electronegative elements like F, O, N, responsible for high boiling and melting point of water
• Dispersion forces (London forces)


  • Very weak, acts in very small distances, formed due to attraction between positively charged nucleus and negatively charged electron cloud, strength is inversely proportional to distance raised to the 7th power
• Substance


  Intermolecular force
• Surface tension


  Phenomenon caused by cohesive forces (intermolecular forces) between molecules allowing liquids to create a thin film on its surface, stronger intermolecular bonds equates to stronger surface tension
• Surface tension


  • Basilisk lizard or the Jesus lizard being able to walk on water
• Concave meniscus


  Occurs when there is stronger adhesive force between the container and the liquid than the liquid's molecules, causes the liquid to climb up the sides of the container
• Convex meniscus


  Occurs when there is stronger cohesive force between the liquid's molecules than the adhesive force between the liquid and the container, causes the liquid to create a dome shape on its surface
• Adhesion


  Interaction between different materials touching each other
• Cohesion


  Interaction between same materials
• Viscosity


  Resistance of a liquid to flow, higher viscosity means thicker consistency, stronger intermolecular forces leads to higher viscosity
• Capillary action


  Phenomenon wherein a liquid is able to rise up on a narrow tube, adhesive forces between the tube and the liquid allow the liquid to exceed its weight
• Evaporation/vaporization


  Process of turning liquid into gaseous form, weaker intermolecular forces equates to greater volatility
• Boiling point


  Solutions with stronger intermolecular forces have higher boiling points than solutions with weaker intermolecular forces