Orbital size effect

Two JC Component System. Vahdation of Orbital Size Effect... 

S Two K Component System. Validation of Orbital Size Effect on the Magnitude of Facial Selectivity... 

Luo, Y. R. (2003). Bond Dissociation Energies of Organic Compounds, CRC Press. Caveat one has to be careful not to attribute the BDE trends solely to the orbital size effects. Other factors (e.g. polarization, hybridization, conjugation, hyperconjugation, non-bonding electron repulsion) are in play as well as will be discussed in more detail in the subsequent parts of this hook. 

The methide ion is the strongest base because the single negative charge is concentrated in a much smaller molecular orbital than any of the others. This orbital size effect even overcomes the trend in electronegativities (H, 2.1 C, 2.5 N, 3.0 O, 3.5 and F, 4.0). 

As an example, Figure 7-21 shows that the — 3 orbitals of the copper atom have their maximum electron densities at similar distances from the nucleus. The same regularity holds for all other atoms. The quantum numbers other than tt affect orbital size only slightly. We describe these small effects in the context of orbital energies in Chapter 8. 

The prototype FeCr sigma phase is of particular interest because the free atoms have very nearly the same size (ratio = 1.01), but they condense into a rather intricate structure. In the pure metals, the diameter of Cr is 2.50 A, while that of Fe is 2.48 A. (a difference of less than one percent), and both are bcc. Therefore, the existence of the sigma phase is determined by spd-hybridization of the electron orbitals. It is sometimes called a size-effect phase, but this is not really descriptive. 

Before investigating the qualitative concepts of the VSEPR model it is worth noting that the details of the interactions between the electron pairs have been ascribed to a size-Pauli exclusion principle result . But objects do not repel each other simply because of their sizes (i.e. interpenetrations) only if the constituents of the objects interact is any interaction possible10). If we are to use the idea of orbital size at all we must avoid the danger of contrasting a phenomenon (electron repulsion) with one of its manifestations (steric effects). The only quantitative tests which we can apply to the VSEPR model are ones based on the terms in the molecular Hamiltonian specifically, electron repulsion. 

Similarly, one may ask how AF110111 would be expected to change in the series C—F, C—Cl, C—Br, and C—I or the series HF, HC1, HBr, and HI. The situation is simpler for these series, since both the electronegativity and orbital size vary but have the same effect on the bond dissociation energy. Variation in orbital size is approximately pro-... 

The last requirement to be met is that the metal d orbitals are close enough in energy to the C—H and H—H orbitals for effective interaction to take place. This requirement is readily met across most of the first and second transition row series. The energies of the d orbitals sweep a broad range as the atomic number and formal oxidation state are changed, and the size, shape, and energy may be finely tuned by the appropriate choice of ligands. 

The observations that there is an "optimum" orbit size and that peaks split for orbits not too much larger than the optimum orbit suggest that the optimum orbit occurs because of special circumstances. One possible circumstance is a coincidence of frequencies for ions with low and high z-mode amplitudes so that if there are mass discriminating differences in the way the ions populate the trap or in the way ions are excited, then systematic mass measurement errors can be expected. Excitation of the cyclotron mode does produce a spread in cyclotron radii, and mass discriminating z-mode excitation is discussed elsewhere in this chapter. Thus, frequency variations that cause systematic mass errors are due in part to trap field inhomogeneities. These effects are evident at low ion populations and may be due in part to excitation induced ion cloud deformation which increases with ion number. 

Keywords nanoparticles, magnetic anisotropy, orbital moment, size effects, superparamagnetism, magnetic dynamics. 

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