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where and are the magnitude of the charges, is their separation, the permittivity of free space and the relative dielectric constant of the medium in which the charges are placed (if you do not remember this consult your high school Physics textbook!). The strictly correct way to use the law would be to consider every nucleus and electron seperately, plug it into the Schrödinger equation and apply quantum chemical methods to solve the equation for the spatial configuration of nuclei we are interested. As already mentioned this is completely impractical for biomolecular systems. So instead we wish to develope a useful model for the interactions between nuclear centres (commonly called "atoms") without having to explicitly deal with the electrons in a system.
The simplest approach is just to place formal charges on each atom which is chemically regarded as charged e.g., a lysine residue would have a charge on +1 electons on its terminal nitrogen atom. Because it is The most common approach is to place a partial charge at each atomic centre. This is a charge which can take a fraction of an electron
Click here if you would like to see an example of a salt bridge.
Induction and Dispersion
Repulsion terms
Hydrogen bonding
On to next course unit The effect of solvent and hydrophobic interactions