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TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Chemistry > Van der Waals and permanent dipole forces

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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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