What is the difference between London dispersion forces and hydrogen bonds?

Both are a type of intermolecular forces which means they act between more than 1 molecules. Do not confuse them with intramolecular forces acting within 1 molecule. London dispersion forces act between all the molecules due to the fluctuations in the electron cloud. Electrons are constantly moving and creating instantaneous dipoles which last only for a very short time. Position of the electrons determines attraction or repulsion between neighbouring molecules. The larger the size of the electron cloud (i.e. the more electrons), the stronger the forces. In hydrogen bond - hydrogen atom of one molecule binds to the nitrogen, oxygen or fluorine atom with a lone pair of electrons of another molecule. It is easy to remember with the abbreviation. - HNOF. Hydrogen bonds are represented with a dotted line. Often there is delta + next to the hydrogen which means slightly positive charge and delta - next to the electronegative atom (N,O,F) representing slightly negative charge. H-bonds are stronger than London dispersion forces, but not as strong as covalent or ionic bonds.