Inert gas: electronic structure

On the basis of contemporary electronic theory of atomic structure we con classify the different types or valence. The guiding principle is that the atoms tend to assume an inert gas electronic structure of eight electrons in the outer shell (ill the ease of hydrogen it is two). To do this, the atom either luses to, gains from, or shares with other atoms, electrons. This process leads to molecule formation. The following are Ihe principal types of valences and their electronic interpretation. 

Covalent bonding (shared electron pairs) is common between identical atoms or atoms having similar electrical properties, such as in H2O, F2, CH4, and C (diamond). In covalent bonding the electrons are shared between atoms so that each atom attains the inert gas electronic structure. For example,... 

In the electron configurations of Table 2.9 there is a systematic build-up process to the filled electron configurations of the inert gas core structures, namely ... 

Indicate the electron rearrangement (gain or loss) in each kind of atom assuming it attains inert gas-like electron structure in the following reactions. 

The identification of unknown chemical compounds isolated in inert gas matrices is nowadays facilitated by comparison of the measured IR spectra with those computed at reliable levels of ab initio or density functional theory (DFT). Furthermore, the observed reactivity of matrix isolated species can in some instances be explained with the help of computed reaction energies and barriers for intramolecular rearrangements. Hence, electronic structure methods developed into a useful tool for the matrix isolation community. In this chapter, we will give an overview of the various theoretical methods and their limitations when employed in carbene chemistry. For a more detailed qualitative description of the merits and drawbacks of commonly used electronic structure methods, especially for open-shell systems, the reader is referred to the introductory guide of Bally and Borden.29... 

Sulfur exists in two crystalline forms, rhombic and monoclinic, the latter comprising three axes of unequal length, two of which intersect at right angles. The bonding within each crystal lattice is covalent and with an electronic structure approaching the configuration of an inert gas atom, the element shows purely nonmetallic chemistry. 

The positive S.P. observed when gases are adsorbed on a metal surface has been atrributed to (a) polarization of the adsorbate by the electron field of the metal double layer 73) and (6) charge-transfer effects 103). The importance of charge-transfer forces has been stressed by Mulliken 87) in his general theory of donor-acceptor interaction. If, as suggested, these charge-transfer forces contribute to the van der Waals attraction, then they probably take part in the physical adsorption process. The complex M X resulting from the adsorption of an inert gas on a metal surface M has been described as essentially no-bond with a small contribution from the structure As seen in Table VI, the S.P., and hence... 

The bonding between the metal and the cyclopentadiene rings involves the it electrons of the two rings, all carbons being equally bonded to the central ferrous ion. The latter, in accepting a share of 12 tt electrons from two cyclo-pentadienyl anions, achieves the 18 outer-shell electron configuration1 of the inert gas, krypton. Analysis of the structure of crystalline ferrocene shows... 

Ferrocene is only one of a large number of compounds of transition metals with the cyclopentadienyl anion. Other metals that form sandwich-type structures similar to ferrocene include nickel, titanium, cobalt, ruthenium, zirconium, and osmium. The stability of metallocenes varies greatly with the metal and its oxidation state ferrocene, ruthenocene, and osmocene are particularly stable because in each the metal achieves the electronic configuration of an inert gas. Almost the ultimate in resistance to oxidative attack is reached in (C5H5)2Co , cobalticinium ion, which can be recovered from boiling aqua regia (a mixture of concentrated nitric and hydrochloric acids named for its ability to dissolve platinum and gold). In cobalticinium ion, the metal has the 18 outer-shell electrons characteristic of krypton. 

The structures for small Si clusters were verified in several experiments. Small clusters can be soft-landed on an inert gas matrix, permitting Raman4 or IR5 spectroscopy. This confirmed the Sin geometries for n < 7. Further proof came from vibrationally resolved photoelectron spectroscopy (PES),6 which exposed some normal modes of anions as overtones on the photoelectron spectra. The electronic transitions also contain structural information about anions.7 PES established a major difference between Sig and Si6, revealing the charge-dependence of Si cluster geometries (Fig. 2).7... 

---