Intermolecular forces

Intermolecular forces

1. Van der waals-the weakest intermolecular force

   • temporary dipole
   • can occur in all kind of molecules
   • work in addition to other intermolecular forces
   • dipole moments are formed by the changing position of an electron cloud. the larger the molecule, the greater the force.

2. Dipole-dipole_weaker than hydrogen but stronger than van der waals

   • permanent dipole
   • occurs in polar molecules
   • all the polar bonds in a molecule add up to give an uneven charge distribution across the whole molecule. Dipole moments depend on the 3D shape of the molecule.
   • eg. Trichloromethane, HCl, Hydrogen sulfide.

3. Hydrogen- strongest intermolecular force

   • occurs in molecules in which a hydrogen atom is bonded to either flourine, oxygen or nitrogen.
   • molecules are needed to have atleast one lone pair of electrons
   • when any of flourine, oxygen or nitrogen bond to hydrogen a very strong dipole forms were hydrogen has a partially positive charge and the other atom has a strong negative charge.
   • eg. HF, H2O, NH3