Fast-moving dipoles

ELECTROMAGNETIC FIELD INTERACTION WITH FAST-MOVING DIPOLES... 

Let us first deal with the dispersion (London) interaction. This interaction is of a non-polar nature, in a non-polar liquid such as carbon tetrachloride, London s dispersion interaction is the only force present between two molecules. These non-polar molecules do not possess any permanent dipole moment. The interaction is a resultant of Instantaneous dipoles formed between the nuclei and electrons at zero-point motion of the molecule. Dispersion forces are weak. When two non-polar molecules of the same type approach each other closely enou for their electronic orbitals to overlap, the weak attraction changes to repulsion. Thus, non-polar molecules exist in a state of random distribution to give a disordered array. Another non-polar molecule (whether a solute or a solvent) will mix in all proportions since neither kind of the molecule has any attraction between them. From the foregoing, it is easy to understand that a non-pK)lar solute molecule will interact more with the phase which is non-polar this solute molecule will move fast if the non-polar phase is the mobile phase or will be retarded more and move slowly if the non-p>olar phase is the stationary phase. 

Let us now deal with the polar interactions. The first kind to be discussed is the dipole-dipole interaction. The solvent whose molecules have permanent dipoles exhibits much more intermolecular attraction as compared to the non-polar molecules. Thus only those solute molecules, which exert either a higher or at least equal attraction with the solvent molecules as compared to the attraction of solvent molecules for each other, will be able to mix with the solvent molecules. Therefore, a polar sample component will interact more with the phase which is itself polar and move fast or be retarded more depending on whether the polar phase is the mobile phase or the stationary phase respectively. 

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