Intermolecular forces

What are intermolecular forces?

The bonds that exist between neighbouring covalent molecules

What are London (Van der Waals) forces? (2)

The force of attraction between the instantaneous and induced dipoles of two adjacent molecules

Occurs in all molecules

How do London forces occur? (4)

Electrons in a molecule are moving randomly - at one point the electrons can be more on one side

This creates an instantaneous dipole in the molecule

This instantaneous dipole causes an induced dipole in the neighbouring molecule

The force of attraction between the two dipoles is a London force

What are permanent dipole forces? (2)

The electrostatic forces of attraction between the partially positive and partially negative dipoles of neighbouring molecules

Only occurs in polar molecules

What is hydrogen bonding? (3)

Can occur when an oxygen, nitrogen or fluorine atom (highly electronegative) bonds to a hydrogen atom

The bond becomes highly polarised

The slightly positive hydrogen atom is able to form a hydrogen bond with the lone pair of electrons on the delta negative atom

What is the order of the strength of the intermolecular forces from smallest to largest?

London

Dipole-Dipole

Hydrogen