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The London force is widely considered universal because any molecule or atom that has electrons or an electron cloud will inevitably have moments where one side of the molecule is more negative than the other due to random electron movements in the cloud. This in turn causes the opposite side to be more positive due to a lack of electrons. These moments are incredibly brief, but can result in attraction between certain molecules.
London Dispersion Forces (LDF) are classified as universal because any molecule or atom with any number of electrons will experience some kind of movement. Since electrons are not in a "fixed" position (they are in an electron cloud and move around there), there will be some areas that are more negative than others at certain moments, and those same areas can be more positive in another moment. Because of this, this will result in an uneven distribution of electrons around the molecule/atom, which is basically what LDFs are.
AlyssaYeh_1C wrote:Why is the london interaction considered "universal"?
The reason why the force is considered universal, is because it is always present and attractive for all molecules because all have electrons. The fluctuating electrons distribution causes the fluctuating dipoles.
London dispersion forces or induced dipole-induced dipole interactions are universal because this type of interaction occurs between any two molecules due to the fluctuating electron densities of the individual atoms of a molecule which results in temporarily positively charged and negatively charged regions that will be attracted to each other. So, even though a molecule is nonpolar and doesn't have a dipole moment, the electron fluctuations in one molecule will exert a force on the other due to the repulsion between electrons, which will result in poles between created within the molecule that have different charges. The different poles will be attracted to the poles of the other molecule. This will result in induced dipoles that will result in an interaction between any two molecule.
They are considered universal because every molecule, polar or non-polar, has London Dispersion Forces. However, it is important to know that London Dispersion Forces are the most prominent intermolecular force in non-polar molecules.
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