Topics - Dispersion-Interaction
Dispersive interactions are one of the three basic interactive mechanisms that allow molecules to exert forces on one another (i.e., dispersive, polar and ionic). Dispersive forces (or London.s dispersive forces
as they were once known) are not due to permanent dipole or induced permanent dipole interactions, or due to interactions between permanent charges on the molecules as in ionic interactions, but are due to transient, random charges, spontaneously generated continuously all over the molecule. Glasstone gave a good definition of dispersion forces, “-although the physical significance probably can not be clearly defined, it may be imagined that an instantaneous picture of a molecule would show various arrangements of nuclei and electrons having dipole moments. These rapidly varying dipoles when averaged over a large number of configurations would give a resultant of zero. However, at any instant they would offer electrical interactions with another molecule resulting in interactive forces.”
Dispersive forces are the only type of molecular force that can exist to the exclusion of all others (e.g., interaction between one hydrocarbon and another).Polar interactions are always accompanied by dispersive interactions and ionic interactions usualy accompanied by polar interactions and always accompanied by dispersive interactions.