Corey-Pauling-Koltun space-filling molecular models

If we model each atom in a molecule as a sphere of radius equal to the van der Waals radius of the atom (for bonded atoms, these spheres overlap, and the spheres of bonded atoms are truncated), the van der Waals surface of a molecule is defined by the outwardfacing surfaces of these atomic spheres. The van der Waals surface is what one sees in the familiar space-filling CPK (R. B. Corey-Pauling-Koltun) molecular models. In discussing intermolecular interactions, the MEPs in the regions on and outside the van der Waals surface are most significant. 

Figure IIB. A space-filling representation of the framework drawing of psilocin depicted in Figure llA. The molecular structures depicted in the figures in this chapter are two-dimensional, line-drawing representations of the molecules that show how the atoms are connected and allow for ready comparison of similarity between molecules. Molecules actually have three-dimensional shapes in which each of the constituent atoms occupies a volume defined by its cloud of electrons. Linus Pauling and two of his colleagues, Robert Corey and Walter Koltun, first developed a form of molecular models to depict the 3-dimensional space-filling aspect of molecules in the way shown in this figure.

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