Lecture on Liquids and Solids

Intermolecular Forces

• Intermolecular vs Intramolecular Forces
  • Intermolecular: Forces between separate molecules.
  • Intramolecular: Forces within a molecule, e.g., covalent bonds.
• Types of Intermolecular Forces
  • Dipole-Dipole Forces: Occur between polar molecules (e.g., HCl).
  • Hydrogen Bonding: Strong dipole-dipole force; involves hydrogen bonded to F, O, or N.
  • London Dispersion Forces: Present in all molecules, especially significant in nonpolar molecules; depend on size and surface area.
  • Ion-Dipole Forces: Present in mixtures, involve ions and polar molecules; generally stronger than hydrogen bonding.

Impact on Bulk Properties

• Boiling and Melting Points: Higher intermolecular forces lead to higher boiling/melting points.
• Surface Tension: Greater with higher intermolecular forces; e.g., water bugs walking on water.
• Viscosity: Higher with stronger intermolecular forces; relates to how thick a liquid pours.
• Vapor Pressure: Inversely related to intermolecular forces; lower with stronger forces.

Phase Diagrams

• Understanding Phase Diagrams
  • Plot of pressure vs. temperature.
  • Indicates regions of solid, liquid, and gas.
  • Lines of Equilibrium: Where two phases are in equilibrium.
  • Triple Point: All three phases in equilibrium.
  • Critical Point: Beyond this, no liquid-gas phase transition.

Unique Phase Diagrams

• Water
  • Solid-liquid line has a negative slope due to hydrogen bonding.
  • Ice is less dense than liquid water.
• Carbon Dioxide
  • At 1 atm, sublimates directly from solid to gas.
  • No normal melting/boiling point at 1 atm.