Filled shell configuration

Active Figure 15.11 Energy levels of the five cyclopentadienyl molecular orbitals. Only the six-7r-electron cyclopentadienyl anion has a filled-shell configuration leading to aromaticity. Sign in at www.thomsonedu.com to see a simulation based on this figure and to take a short quiz. 

The noble gases are the only elements that exist naturally as individual atoms. Electron configurations make it clear why noble gas atoms prefer to remain as single atoms. Each noble gas has a filled shell configuration 1 for He and for the others. All electrons are paired, and there are no vacant... 

The filled shell configuration for the ground state transforms as... 

Similarly, 6-electron main group species show chemical similarities with 16-electron organometallic species. As for the halogens and 17-electron organometallic complexes, many of these similarities can be accounted for on the basis of ways in which the species can acquire or share electrons to achieve filled shell configurations. Some similarities between sulfur and the electronically equivalent Fe(CO)4 are listed in Table 15-2. 

Energy levels of the five cyclopentadienyl molecular orbitals. Only the ix-ir-electron cyclopentadienyl anion has a filled-shell configuration leading to aromaticity. 

Hence the diradical states are exceptional in that the epikernel principle cannot be based on the usual first order JT section rule of Eq. (1) The reason is that the E state is essentially based on a half-filled shell configuration, with two electrons in a doubly degenerate e" orbital. As we have shown elsewhere such half-filled shell states are subject to a hole electron exchange symmetry, which counteracts the first order JT distorting forces [42], Moreover, in these highly reactive molecules the absence of a strong first order activity coincides with a pronounced second order effect, due to suitable low lying excited states. This limits the applicability of the epikernel principle in the case of diradicals. 

EA s of metal clusters are measured through photoelectron spectroscopy of anionic clusters. Clusters that are just short of a filled shell configuration should have large EA s. This is indeed borne out in experiments. EA s of Cu, clusters measured by Pettiette et al. [21] show sharp drops after N=l, 17, 19, 33, aud 39 (Figure 8.5). These clusters are one electron short of filled shell configurations at Af = 8,18,20,34,... 

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