AS 1016 Chemsheets AS 1016 (Forces between molecules).

1) Van der Waals' forces (also called induced dipole
• Even in molecules with no polar bonds, there are
constant movement of electrons.
• This induces a temporary dipole in a neighbouring molecule, producing a temporary induced dipole
• The bigger the molecule (i.e. the more el
C3H8 boiling point -42°C).
2) Permanent dipole-dipole attraction
• Some molecules with polar bonds have an overall dipole (e.g.
dipoles cancel each other out)].
• There are attractions between these permanent dipoles in neighbouring molecules (e.g. between H
3) Hydrogen bonding
• This is a special case of permanent dipole
atom (i.e. F, O, N)
• The polar bond leaves the H nucleus exposed as H only has one electron.
• Therefore there is a strong attraction
another molecule.
• This is simply a strong intermolecular force
e.g. NH3
e.g. H2O
e.g. HF