Electron Au

A different density surface (0.002 electrons/au ) serves to portray overall molecular size and shape. This is, of course, the same information portrayed by a conventional space-filling (CPK) model. ... 

In the discussions which follow in this chapter and in the remainder of this guide, a 0.1 electrons/au isodensity surface will be referred to as a bond surface and a 0.002 electrons/au isodensity surface either as a size surface or more simply as a density surface. 

Because of the contraction and stabilization of the 6s orbital, the outermost, or valence, shell of Au is formed by both the 5d and 6s orbitals. Indeed, electronically, Au is halogen-like, with one electron missing from the pseudo noble gas (closed subshell) configuration. Hence, similar to the existence of halogen X2 molecule, gold also forms the covalent Au2 molecule. In addition, gold also forms ionic compounds such as RbAu and CsAu, in which the Au- anion has the pseudo noble gas electronic configuration. 

Elements Metal Cations in a sea of electrons Au Metallic bond... 

Remember, there are five d-orbitals that are grouped according to symmetry, and each orbital can hold up to two electrons. AU the orbitals that have the same symmetry are expected to have the same energy level (degenerate), so they are placed alongside each other. The orbitals are represented as boxes that can be filled with arrows, that represent the electron and the spin. The electrons can either be spin up with an arrow pointing up, or spin down with an arrow pointing down, this follows from the Pauli exclusion principle (see Chapter 2). 

The molecular structures of the five homoleptic noble gas compounds that are stable enough to be studied in the gas phase are shown in Fig. 19.1. If the noble gas atoms are assumed to form single electron pair bonds to the fluorine atoms, and if the Xe-O bonds in Xe04 are assumed to be double (four electron bonds), then the K and Xe atoms in the trifluorides are surroimded by 10 electrons in the valence shell, the Xe atom in XeP4 by 12, the Xe atom in XeP6 by 14, and in Xe04 by 16 electrons. AU these compounds may thus be described as containing hypervalent noble gas atoms. 

Notice that the arrangement of atoms is the same in each structiue—only the placement of electrons differs. In writing resonance structures, the same atoms must be bonded to each other in all structures, so that the only differences are in the arrangements of electrons. AU three N03 Lewis structures are equally dominant and taken together adequately describe the ion, in which all three N—O bond lengths are the same. 

The effective unpaired electron densities and total number of effectively unpaired electrons (Au) were computed [39-41]. To avoid overemphasizing the contribution of the natural orbitals (NOs) that are nearly occupied or nearly unoccupied, we chose to use the nonlinear model suggested in [41] where iVu is given by... 

When the energy barrier proves to be much greater than the thermal energy of the electrons (AU kT), the number of electrons that manage to overcome this barrier becomes negligible. 

Other equivalent expressions have been given (Hianenz and Rajagopalan 1997). As with the previously discussed dipole interactions. Equation 4.13 shows a short-range interaction, with also an exponent -6 in the distance. Because the London interactions do not require the presence of charges and depends solely on polarizabilities (i.e., the mobility of electrons) aU ions, atoms, molecules, or particles are affected by them. 

The azimuthal quantum number I determines the orbital angular momentum of the electron. AU the quantum states with the same values of and I make up a subshell. 

Figure 12.2 Graphical illustration of the delocalized spin density distribution (hlack positive spin white negative spin spin isosurface value = 0.0003 electron au ) of the radical cationic state of the nitrogen-hridged [iMjpara-(yclophane derivative 12.7b (Scheme 13.4).

The interaction of bare monovalent (alkah metals and coinage metals) and divalent (alkaline earth and zinc group metals) cations with the N7 site of piuine NA bases was examined in gas phase using MP2/6-31G(d,p)//HF/6-31G(d,p) level of theory (Burda et al. 1996). A graphical illustration of the dependence of the coordination distance on the atomic number of the cations is displayed in O Fig- 36-1. The intermolecular M-N7 distance monotonicaUy increase with the atomic numbers for the alkali metals and metals of alkaline earths (cf. O Fig. 36-1). This increase of the distances is more pronounced for the alkali metals where it exceeds 1 A. The calculated M-N7 distances for both types of metals correlate well with the known ionic radii, e.g.. Tide (1977). The influence of the relativity for the 5s and 5p electrons (Cs, Ba ) is not as pronounced as for the 5d electrons (Au, Hg ) (Pyykko 1988). 

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