3 phases - dependent on the intermolecular forces

• gas
  • takes on volume/shape of container
  • compressible
  • flows easily
  • diffusion occurs rapidly
• liquid
  • takes on shape of container
  • doesn’t expand to fill container
  • incompressible
  • flows readily
  • diffusion occurs slowly
• solid
  • keeps its own shape/volume
  • incompressible
  • doesn’t flow
  • diffusion occurs very slowly

intermolecular forces - much weaker than ionic/covalent bonds

• molecules remain intact when intermolecular forces broken
• stronger intermolecular forces >> higher melting/boiling points
• van der Waals forces - intermolecular attractive forces between neutral molecules
  • dipole-dipole, London dispersion, hydrogen bonding
• ion-dipole force - between ion and partial charge on an end of polar molecular
  • ion charge increase or dipole moment magnitude increase >> increase in magnitude of attraction
  • important for solutions of ionic substances in polar liquids
• dipole-dipole force - attraction between positive/negative ends of neutral polar molecules
  • only effective when polar molecules very close together
  • increasing polarity >> increasing intermolecular attractions
  • smaller molecules >> increasing attraction
• London dispersion force - instantaneous dipole moment
  • found between nonpolar and polar molecules
  • due to temporary dipole moments at particular moments
• polarizability - how easily an electric field can change the molecule’s charge distribution
  • increasing molecular weight >> increasing strength of dispersion forces
  • most massive/polar molecules have largest attraction forces
• hydrogen bonding force - intermolecular attraction between hydrogen atom in polar bond and unshared electron pair on another molecule
  • generally stronger than dipole-dipole/dispersion forces
  • hydrogen’s small size lets it get close to electronegative atom
  • equal amounts of water take up more volume as solid than as liquid (usually reversed for other substances)