[Terminology] Van Der Waals force
Van Der Waals force is the force that attracts between molecules and promotes the aggregation of molecules. Van Der Waals force is a kind of intermolecular force, which exists widely.
Intermolecular interactions are mainly composed of the following three types:
(1), Permanent dipole - Permanent dipole interaction
Exist between polar molecules. Depending on the permanent dipole of polar molecules, generate interaction force. The force is called orientation force.
At the same time, the orientation force makes the polar molecules closer and the positive and negative centers of the polar molecules more separated. Therefore, there is still the induced force between the polar molecules.
(2), Permanent dipole - Induced dipole interaction
Exist between polar and nonpolar molecules. Depending on the permanent dipole of polar molecules and the induced dipole of nonpolar molecules, generate interaction force. The force is called induced force.
Under the influence of polar molecules, nonpolar molecules will produce induced dipoles.
(3), Instantaneous dipole - Instantaneous dipole interaction
Exist between any molecules. Depending on the instantaneous dipole of molecules, generate interaction force. The force is called dispersion force.
Due to the instantaneous displacement between nuclei and electrons in molecules, the positive and negative centers are separated, thus generate instantaneous dipole.
Among the three forces of orientation force, induced force and dispersion force, dispersion force is the most basic. For most molecules, except for some highly polar molecules (such as water), the dispersion force is also the most important.
Van Der Waals force is a weak force, and its action energy is about 1-2 order of magnitude lower than that of chemical bond. Unlike covalent bond, Van Der Waals force has no directionality and saturation.
Van Der Waals force mainly affects the physical properties such as melting point, boiling point and solubility of substances, and will not affect the chemical properties of substances.
In the colloidal system, the flocculation of particles is also the embodiment of Van Der Waals force.