LONDON FORCES

aka van der Waals forces
cause all atoms and molecules to be attracted to each other
electron charge clouds are always moving, at a specific moment electrons in one atom are more likely to be to one side than the other. This creates a temporary dipole.
this dipole can cause another temporary dipole in the opposite direction on neighbouring atom(s), this results in them being attracted to each other. (instantaneous dipole-induced dipole interactions).
electrons are constantly moving, so dipoles are being created and destroyed all the time
larger molecules have larger electron clouds, meaning stronger London forces.
molecules w/ greater S.A. have stronger London forces, as more of their electron cloud is exposed.

HYDROCARBONS:

LONGER CHAINS HAVE MORE MOLECULAR S.A., MORE ELECTRONS INTERACT SO STRONGER LONDON FORCES.
BRANCHED-CHAIN ALKANES HAVE SMALLER MOLECULAR S.A. AND CANNOT AS CLOSELY TOGETHER, SO LONDON FORCES ARE LOWER.
THUS LONG-CHAIN AND STRAIGHT-CHAIN ALKANES HAVE HIGHER BOILING POINTS.

	Created by Annabelle Kennedy over 10 years ago

university CHEMISTRY Note on intermolecular forces, created by Annabelle Kennedy on 23/05/2014.