WEEK2- Intermolecular Forces

• Dipole-dipole force


  Exists between the partially positive end of one molecule and the partially negative end of another
• Ion-ion interactions

  • table salt, sodium and chloride ions
• Four main types of intermolecular forces

  • London dispersion forces
  • Dipole-dipole forces
  • Hydrogen bonding forces
• Many unusual properties of water are attributed to hydrogen bonding
• Ion-ion interactions are ionic bonds, not part of intermolecular forces
• Dipole-dipole force exists between polar molecules described as dipoles
• Hydrogen bonding is a special type of Dipole-dipole force depending on partial charges
• In water

  The hydrogen of one molecule is attracted to the unshared electron pair of an oxygen atom in another molecule
• Intermolecular forces are attractive forces present in between molecules
• Dipoles


  High difference in electronegativity, creating partial charges within a molecule
• Ion-ion interactions are also known as ionic bonds
• London dispersion forces are the weakest type of intermolecular forces and are present between all non-polar molecules
• Hydrogen bonding


  • between formaldehyde and water
• Induced dipoles occur when a nonpolar atom becomes polar due to the presence of an ion or a dipole
• All electrically neutral molecules exhibit London dispersion forces (LDF)
• London dispersion forces (LDFs)


  Are present in between all electrically neutral molecules—polar and nonpolar molecules
• Hydrogen bonding and Dipole-Dipole Forces depend on Partial Charges
• Formation of instantaneous dipole

  • Observed in nonpolar molecules such as O2
• Polarizability is the measure of how easy it is to distort the electron distribution of a molecule
• Intermolecular forces of attraction are attractive forces present in between molecules
• London Dispersion Forces


  Temporary dipoles between nonpolar molecules
• The strength of LDFs depends on the polarizability of the molecule
• London Dispersion Forces are the weakest type of IMFA
• Some molecules have polar bonds but are nonpolar as a whole due to the cancellation of the dipole moment
• Hydrogen bonding is a special type of Dipole-Dipole Force
• Hydrogen bonding


  Exists when hydrogen is bonded to the most electronegative atoms, namely F, O, or N
• Dipole-dipole interactions


  Are attractive forces present in between polar molecules
• How are temporary/Induced dipoles created?

  A nonpolar molecule has an equal distribution of charges. At any instant, an instantaneous dipole may form. The instantaneous dipole may induce the formation of another dipole (induced dipole)
• Nonpolar covalent compounds have zero dipole moment and exhibit London dispersion forces