The electronic charges and the positions of the centers of these charges have been calculated for the atoms of a number of second- and third-row heteronuclear diatomic molecules. For both the oxygen and the fluorine atoms, the charge associated with one of these atoms can be correlated, within a series of molecules containing that atom, with both the orbital energy of the atom's ls electrons and also with the difference in electronegativities of the atoms that comprise the molecule. The centers of electronic charge are outside of the internuclear regions, except for the positive atoms in the more ionic molecules and in HF. The first two papers in this series have dealt with two different properties of atoms in molecules. In Part I, a method was presented for determining the quantity of electronic charge associated with an atom in a molecule [,1], while Part II was concerned with the calculation of the position of the center of this charge [-2]. The basis of the proposed procedure is the partitioning of the space of the molecule into regions "belonging" to the individual atoms [-1]. The electronic charge associated with a given atom A is then given by QA= ~ ~(r)dr A