Intermolecular forces

• What are permanent dipole-dipole forces?

  The electrostatic attractions between the partial positive end of one polar molecule and the partial negative end of another.
• What are hydrogen bonds?

  The force of attraction between the slightly positive hydrogen atom in one molecule and the lone electron pair on the N,O/F atom in another molecule.
• Rank the strengths of the intermolecular forces

  1. Hydrogen bonds
  2. Permanent dipole-dipole
  3. Van Der Waals
• How do hydrogen bonds arise?

  A molecule must contain a H atom and the neighbouring molecule must have a N/F/O atom
• What are the impacts of hydrogen bonding on properties?

  greater solubility in water

  higher mp/bp compared to similar sized molecules
• What are induced dipole-dipole forces?

  Temporary fluctuations in the electron distributions around atoms.
• How do induced dipole-dipole forces arise?

  Electons in atoms are constantly moving. At any instance, there may be more e- on one side of the atom than the other, creating a temporary dipole which can induce an opposite dipole in a neighbouring atom, causing weak electrostatic attractions between the atoms.
• What factors affect the strength of induced dipole-dipole forces?

  the strength increases with size of molecules and surface area of the atoms/ molecules
• How does size affect the strength of induced dipole-dipole forces?

  Larger atoms/molecules have more e- and a greater volume of electron density that can become polarised, creating a stronger temporary dipole.
• How does surface area affect the strength of induced dipole-dipole forces?

  Molecules with larger surface area also have stronger induces dipole-dipole forces as more of the e- cloud is exposed for interactions.