Electronic configurations, closed-shell

Elements at the right of the periodic table tend to gam electrons to reach the elec tron configuration of the next higher noble gas Adding an electron to chlorine for exam pie gives the anion Cl which has the same closed shell electron configuration as the noble gas argon... 

The covalent, or shared electron pair, model of chemical bonding was first suggested by G N Lewis of the University of California m 1916 Lewis proposed that a sharing of two electrons by two hydrogen atoms permits each one to have a stable closed shell electron configuration analogous to helium... 

Irons of benzene are distributed in pairs among its three bonding tt MOs giving a closed shell electron configuration All the bonding orbitals are filled and all the electron spins are paired... 

Closed shell electron configuration (Sections 1 1 and 116) Stable electron configuration in which all the lowest energy orbitals of an atom (in the case of the noble gases) an ion (e g Na" ) or a molecule (e g benzene) are filled... 

Figure 11.15 shows the Fliickel MOs of cyclopentadienyl anion. Like benzene and cyclo-heptatrienyl cation, cyclopentadienyl anion has six tt electrons and a closed-shell electron configuration. 

As a consequence of its closed-shell electron configuration, zinc has a negative electron affinity, that is, the removal of an electron from Zn is exothermic. The electronegativity of zinc (1.588 PU) is intermediate between those of the alkaline earth metals and the first row transition metals and remarkably similar to that of beryllium (1.57 PU). 

Each atom in structure 3 has a closed-shell electron configuration and a formal charge of zero. We can complete the octet for the carbon and nitrogen atoms in structure 1 by converting a lone pair of electrons on each nitrogen atom into a covalent bond to the central carbon atom. 

Most stable ground-state molecules contain closed-shell electron configurations with a completely filled valence shell in which all molecular orbitals are doubly occupied or empty. Radicals, on the other hand, have an odd number of electrons and are therefore paramagnetic species. Electron paramagnetic resonance (EPR), sometimes called electron spin resonance (ESR), is a spectroscopic technique used to study species with one or more unpaired electrons, such as those found in free radicals, triplets (in the solid phase) and some inorganic complexes of transition-metal ions. 

While the vast majority of molecules may be described in terms of closed-shell electron configurations, that is, all electrons being paired, there are several important classes of molecules with one or more unpaired electrons. So-called free radicals are certainly the most recognizable. One way to treat open-shell molecules is by strict analogy with the treatment of closed-shell molecules, that is, to insist that electrons are either paired or are unpaired. 

There are five possible constitutional isomers of Cyg whose structures possess closed-shell electronic configurations [15, 62]. The two most abundant of these, C2V-C78 and D3-C78 have been studied extensively by CV and OSWV. In the first study carried out at —15°C in PhMe/MeCN, the C2v isomer displays six one-electron reductions, with the sixth one being irreversible. All waves are... 

Cg4 can be any of 24 stable isomers that satisfy the isolated pentagon rule [4, 6] and possess closed-shell electronic configurations [15]. Before successful HPLC separation and characterization of major and some minor isomers was achieved [53, 55, 56], electrochemical studies of Cg4 involved a mixture of its two major isomers, D2(IV) and D2rf (I I), which at the time could only be isolated as a 2 1 mixture [50, 51, 60]. In solvents such as pyridine, PhCN, and DMF/PhMe, the mixture displayed multiple redox waves, making assignment difficult. In the first OSWV study of the separated isomers, D2-Cg4(IV) displayed four one-electron evenly spaced reductions in pyridine (see Table 8 and Fig. 5) [53]. However, the reduction potentials of the isomer reported as 02 (11) in that same study are now believed to correspond to one of the minor isomers of Cg4, the C2 (IV)... 

Huron and Platz recently smdied the photochemistry of 13 in solution by LFP. The triplet state of 19 absorbs at 400 nm in 1,1,2-trifluorotrichloroethane with a lifetime of 1-2 ps. The triplet is formed within 10 ns of the laser pulse. Relaxation of the singlet to the triplet state of 19 is fast relative to the related process in aryl-nitrenes and is comparable to a carbenic process. As we will see later when we discuss intersystem crossing rates of singlet arylnitrenes, this difference is most likely due to the closed-shell electronic configuration of the singlet state of 19. 

Ionic crystals are formed between highly electropositive and highly electronegative elements when electron transfer from the former to the latter occurs, resulting in oppositely charged ions with closed shell electronic configuration. X-ray diffraction studies of ionic crystals reveal an essentially spherical charge distribution around the... 

All of the transitions that make significant contributions to the absorption spectra of the complexes under consideration here have Eu overall symmetry. Since all of the molecules have a closed-shell electronic configuration, their MCD spectra would be expected to have contributions from A and terms. 

No anodic signal was observed for any of these compounds, which is an indication of a rather large HOMO-LUMO gap. Their redox behavior was interpreted assuming a + 2 formal oxidation state for the Yb or Ca atoms and therefore a closed-shell electronic configuration. The electrochemical gap between the third and second cathodic events is larger than between both the second and first events, and the fourth and third events, which suggests that the LUMO of these compounds is nondegenerate. 

If we have more than one d-electron outside a closed shell electronic configuration, then in general there will be several electronic states for the free ion. These states will have different electronic energies and will be characterized by their term symbols (see Appendix... 

The theoretical treatment of bonding and structure of gold clusters has met with considerable success. For the higher gold dusters, the best predictions are that, for a cluster [AutL, 1]"+ in which the peripheral gold atoms define a closed spherical polyhedron, there will be a closed shell electron configuration when 12x + 6 electrons are present. The structures of complexes... 

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