Conclusive evidence is presented whlch shows that the concept
of modified atoms in molecule (MAM) is a viable model for a good
description of numerous molecular properties. Atomic modification .
can be decomposed to isotropic and anisotropic components. The
isotropic change caused by molecular formation is given by the
electric monopoles of atoms. It is a consequence of the charge drift
accompanying chemical bonding. Atomic monopoles reproduce diamagneticshielding of the nuclei rJAd, diamagnetic susceptibility xd
and ESCA shifts with an intriguing success. The atomic monopole
model is easily extended to include higher local multipoles
(i. e. anisotropic contribution), thus yielding satisfactory total molecular
multipoles and extramolecular electrostatic potentials. Salient
directional properties of covalent bonds are well described by the
use of polarized atomic orbitals. It was shown that hybridization
is the underlying concept which explains interrelations between
steric features and local bond properties. Hybridization rationalizes
in a natural and simple way the electron pair (Lewis) bond which
is one of the corner stones of chemistry being particularly important
for the first row atoms. It was concluded that the high
information content of hybrid AOs can be ascribed to the fact
that they conform to the local symmetry of the immediate
molecular environment. Thus the HAOs are local wavefunctions
of the zeroth order which describe atomic angular distortions.
Although atoms can not be uniquely defined within molecules,
the MAM model has high interpretative power yielding reasonable
results. Special attention deserves a picture of charged atoms
immersed in the »sea« of mixed electron density, because it is free
of any arbitrariness in the slicing of molecular volume of partitioning
of overlap charge. Finally, the definition of pseudo-observables
is given. It was concluded that atomic monopoles and hybridization
indices are pseudo-observables par exceHence.
A.pparently there is colour, apparently
sweetness, apparently bitterness; actuaUy
there are only atoms and the void.
Democritus, 420 B. C
