TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Chemistry > Van der Waals and permanent dipole forces
Van der Waals forces
- Act between all atoms and molecules.
- Van der Waals forces are caused by the formation of temporary dipoles due to constant movement of electrons.
- The size of the force depends on the size of the molecule. In a large molecule, there are more electrons therefore the Van der Waals forces between large molecules are stronger than between smaller molecules.
Permanent dipole forces
- Occur between molecules with permanent dipoles.
- Permanent dipoles are formed when there is a large difference in electronegativity between two atoms bonded together in a covalent bond. This causes the shared pair of electrons to be shared unequally. They are pulled towards the more electronegative atom.
- e.g. H---F has a permanent dipole. The shared pair of electrons are shared unequally and are pulled towards the electronegative F atom.
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