The above diagram shows the distortion of the electron cloud due to the weak \(E\) field. Notice that the electron spins around the proton instead of being captured by the weak field. A dipole forms due to the distorted electron cloud that depart further as two aligned particles approach each other. The attraction increases. Repulsion from the electron clouds balances this attractive force. This force is prominent when the particles are restricted from rotation (eg. part of a bond). Free rotation breaks the bond.
In another situation where the electron is held by the weak field,
The electron cloud does not distort. As the particles approach each other the cloud departs and exposed the underlying weak field. Without an initial fixed approach direction (due to a dipole, as the case above), the exposed weak field can be opposing or aligned, resulting in a repulsive force and an attractive force respectively. The dipole on each particle due to the distorted electron clouds always pushes the particles apart.
The forces due to the underlying \(E\) fields are temperature dependent. The forces due to the distortion on the electron cloud are less sensitive to temperature in the first diagram, and the forces are not dependent on temperature at all in the lower diagram.
These two behaviors are exclusive, their nature is the result of the electron in the orbit associating either with the proton or with the \(E\) field. When the electron changes position the corresponding behavior manifests itself.
Van der Waals Forces in part and in parts.
