Forces between molecules

Forces between molecules:

• permanent dipole–dipole forces

• induced dipole–dipole (van der Waals, dispersion, London) forces

• hydrogen bonding.

The melting and boiling points of molecular substances are influenced by the strength of these intermolecular forces.

The importance of hydrogen bonding in the low density of ice and the anomalous boiling points of compounds.

Students should be able to:

• explain the existence of these forces between familiar and unfamiliar molecules

• explain how melting and boiling points are influenced by these intermolecular forces.

AT d and k

PS 1.2

Students could try to deflect jets of various liquids from burettes to investigate the presence of different types and relative size of intermolecular forces.