Properties of atoms in molecules

It is the operational essence of the atomic hypothesis that one can assign properties to atoms and groupings of atoms in molecules and on this basis identify them in a given system or use their properties to predict the behaviour of the system in which they are found. The primary purpose of this section is to demonstrate that the quantum atoms transform this atomic hypothesis into an atomic theory of matter by identifying the atoms of chemistry and defining their properties. This section is not a review of applications, but is rather intended to introduce and illustrate the uses of various atomic properties. 

A check on the accuracy of the numerical integrations of the atomic properties is provided by the evaluation of 1,(12). This quantity, defined in eqn (5.50), is proportional to the integral of the Laplacian of the charge density over the basin of the atom or, equivalently, to the flux in the gradient vector field of p through the surface of the atom, 

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We have discussed the properties of atoms in molecules. What can we find out about the bonds in a molecule We have seen that the bond path shows us where bonds are located in a molecule, that is, which atoms are bonded together because of the accumulation of elec-... 

This chapter is based on the VSEPR and LCP models described in Chapters 4 and 5 and on the analysis of electron density distributions by the AIM theory discussed in Chapters 6 and 7. As we have seen, AIM gives us a method for obtaining the properties of atoms in molecules. Throughout the history of chemistry, as we have discussed in earlier chapters, most attention has been focused on the bonds rather than on the atoms in a molecule. In this chapter we will see how we can relate the properties of bonds, such as length and strength, to the quantities we can obtain from AIM. 

Those who applied quantum mechanics to atoms and molecules had a wealth of chemists data at hand well-defined bond properties including dipole moments, index of refractions, and ultraviolet absorption qualities and polarizability as well as well-defined valence properties of atoms in molecules. If one attempted to set up a wave equation for the water molecule, for example, there were 39 independent variables, reducible to 20 by symmetry considerations. But the experimental facts of chemistry implied or required certain properties that made it possible to solve equations by semiempirical methods. "Chemistry could be said to be solving the mathematicians problems and not the other way around," according to Coulson. 148... 

Bader RFW, Carroll MT, Cheeseman JR, Chang C (1987) Properties of atoms in molecules atomic volumes. J. Am. Chem Soc. 109 7968—7979... 

While the excellence of the agreement of the relative energies of the methylene group in the cyclic molecules with the measured strain energies may be to some extent due to the fortuitous cancellation of errors in the contributions not specifically considered, namely the correlation energy, the zero-point energy, and A AHf) between 0 and 298 K, the nature of the results leaves no doubt as to the correctness of the interpretation that has been given, that the atoms of theory recover the experimentally measured properties of atoms in molecules. 

P. Politzer and E, W. Stout, Jr., Chem. Phys. Lett., 8, 519 (1971). Properties of Atoms in Molecules. The Position of the Center of Electronic Charge in an Atom in a Molecule. 

P. Politzer and P. H. Reggio, J. Am. Chem. Soc., 94, 8308 (1972). Properties of Atoms in Molecules IV. Atomic Charges in Some Linear Polyatomic Molecules. 

Some properties such as overall molecular shape or compactness may depend on the entire topological framework or skeleton. The symmetry or topological equivalence properties of atoms in molecules also depend on the whole molecular structure. Some aspects of symmetry and shape will be discussed later. 

T. Slee, A. Larouche, and R. F. W. Bader, /. Phys. Chem., 92, 6219 (1988). Properties of Atoms in Molecules Dipole Moments and Substituent Effects in Ethyl and Carbonyl Compounds. 

Covalent and van der Waals radii are other fundamental properties of atoms in molecules that are influenced by nuclear charge and electron distribution. A glance at a molecular model or graphic suggests that most atoms have several different dimensions. There is the distance between each bound atom and also a dimension in any direction in which the atom in not bonded to another atom. The former distance, divided between the two bonded atoms, is called the covalent radius. The nonbonded dimension of an atom or group in a molecule is called the van der Waals radius. This is the distance at which nonbonded atoms begin to experience mutual repulsion. Just short of this distance, the interatomic forces are weakly attractive and are referred to as dispersion or London forces and are attributed to mutual polarization of atoms. 

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