KINETIC MOLECULAR MODEL AND INTERMOLECULAR FORCES

• Kinetic Molecular Model


  • Matter in the gas state has indefinite shape and volume
  • Matter in the liquid state has indefinite shape and definite volume
  • Matter in the solid state has definite shape and volume
• Solid


  • Arrangement of particles: closely and orderly packed
  • Kinetic energy of particles: vibrate and rotate about a fixed position
  • Particle motion: very low
  • Attractive forces: very strong
• Liquid


  • Arrangement of particles: less closely packed
  • Kinetic energy of particles: particles slide over each other
  • Particle motion: low
  • Attractive forces: strong
• Gas


  • Arrangement of particles: very far apart
  • Kinetic energy of particles: particles move at great speed
  • Particle motion: high
  • Attractive forces: low
• Polar attraction as a universal law

  • Molecules are held together by electrostatic attraction: Intramolecular attraction within molecules (ionic, covalent, metallic)
  • Molecules are held together by electrostatic attraction: Intermolecular forces between molecules (van der Waals forces)
• Van der Waals forces are named after Dutch scientist Johannes van der Waals (1837 – 1932)
• Types of Bonding


  • Pure/nonpolar covalent <0.5
  • Polar covalent bet. 0.5 and 1.7
  • Ionic >1.8
• Types of van der Waals forces

  • Ion – dipole
  • Dipole – dipole
  • Hydrogen Bonds
  • London Dispersion Forces
• Ion – dipole forces

  Results when an ion and the partial charge found at the end of the polar molecule attract each other
• Dipole – dipole forces


  Exists between neutral polar molecules where positive and negative ends attract each other
• Hydrogen Bonds


  Attractive interaction between a hydrogen atom bonded to an electronegative atom and an unshared electron pair of another nearby electronegative atom
• London Dispersion Forces


  Force of attraction between nonpolar molecules or atoms, originated from Fritz London (1900-1954)
• London Dispersion Forces


  Instantaneous dipole can induce dipoles in neighboring atoms, affecting melting and boiling points