Molecular shapes angular

The VSEPR notation for the Cl2F+ ion is AX2E3. According to Table 11.1, molecules of this type exhibit an angular molecular geometry. Our next task is to select a hybridization scheme that is consistent with the predicted shape. It turns out that the only way we can end up with a tetrahedral array of electron groups is if the central chlorine atom is sp3 hybridized. In this scheme, two of the sp3 hybrid orbitals are filled, while the remaining two are half occupied. 

Some of the chemical concepts with little or no quantum-mechanical meaning outside the Bohmian formulation but, well explained in terms of the new interpretation, include electronegativity, the valence state, chemical potential, metallization, chemical bonding, isomerism, chemical equilibrium, orbital angular momentum, bond strength, molecular shape, phase transformation, chirality and barriers to rotation. In addition, atomic stability is explained in terms of a simple physical model. The central new concepts in Bohmian mechanics are quantum potential and quantum torque. 

All of the information that was used in the argument to derive the >2/1 arrangement of nuclei in ethylene is contained in the molecular wave function and could have been identified directly had it been possible to solve the molecular wave equation. It may therefore be correct to argue [161, 163] that the ab initio methods of quantum chemistry can never produce molecular conformation, but not that the concept of molecular shape lies outside the realm of quantum theory. The crucial structure-generating information carried by orbital angular momentum must however, be taken into account. Any quantitative scheme that incorporates, not only the molecular Hamiltonian, but also the complex phase of the wave function, must produce a framework for the definition of three-dimensional molecular shape. The basis sets of ab initio theory, invariably constructed as products of radial wave functions and real spherical harmonics [194], take account of orbital shape, but not of angular momentum. 

On the basis of the simple rules defined above, the shapes of all molecules can in principle be predicted by logical procedures. It will be argued that any quantitative scheme that takes into account, not only the energy levels of electrons in molecules, but also their angular momenta must yield a comparable result that contains a framework for the definition of three-dimensional molecular shape. A few hydrides and other simple molecules will be discussed to demonstrate the principle. 

The SHAPES force field" has been implemented in CHARMM and used to examine the structures of several square planar rhodium complexes. This force field is based on angular overlap considerations and treats angular distortions for a variety of geometries. Spherical internal coordinates and Fourier potential functions form the basis for the description of these molecular shapes. The parameters for this force field were derived from normal coordinate analysis, ab initio calculations, and structure-based optimizations. The average rms deviation for bond lengths was 0.026 A, and the average rms deviation for bond angles was 3.2°. 

InterScience, New York, 1985 and the related text by T. A. Albright and J. K. Burdett, Problems in Molecular Orbital Theory, Oxford University Press, Oxford, 1992, which offers examples of many problems and their solutions. Discussions of angular overlap and a variety of other aspects of orbital interactions in coordination complexes are provided in J. K. Burdett, Molecular Shapes, John Wiley Sons, New York, 1980, and B. N. Figgis and M. A. Hitchman, Ligand Field Theory and Its Applications, Wiley-VCH, New York, 2000. Discussions of computational method are provided in A. Leach, Molecular Modeling Principles and Applications, 2" ed., Prentice Hall, Upper Saddle River, NJ, 2001, and C. J. Cramer, Essentials of Computational Chemistry Theory and Models, Wiley, Chichester, UK, 2002. 

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