Van der Waals forces are dependent on both atomic size and electron number. These forces arise due to temporary fluctuations in electron distribution within atoms and molecules.
Atomic Size: The magnitude of van der Waals forces is influenced by the size or atomic radius of the atoms or molecules involved. Larger atoms or molecules have more electrons and a greater electron cloud, resulting in a higher polarizability. Polarizability refers to the ease with which the electron distribution can be distorted by an external electric field or the electron distribution of another atom or molecule. As a result, larger atoms or molecules can induce greater temporary dipoles in neighboring atoms or molecules, leading to stronger van der Waals forces.
Electron Number: The number of electrons in an atom or molecule affects its ability to experience and induce temporary dipoles. The greater the number of electrons, the more likely it is for temporary fluctuations in electron distribution to occur. Consequently, atoms or molecules with more electrons tend to have stronger van der Waals forces. This is because the greater number of electrons increases the chances of forming temporary dipoles and enhances the overall attractive interactions between neighboring particles.
In summary, the interplay between atomic size (related to polarizability) and the number of electrons in atoms or molecules determines the strength of van der Waals forces. Larger atoms/molecules with more electrons generally exhibit stronger van der Waals forces due to their increased polarizability and greater likelihood of temporary dipole interactions.