Atomic orbitals closed-shell configuration

He, Be and Ne are examples of atoms with complete orbitals closed-shell configurations). For atoms with incomplete orbitals open-shell configurations) more than one Slater determinant is necessary. 

The spin-orbit interaction considered in the study of monoelectronic atoms also plays an important role in polyelectronic atoms, with the exception of closed-shell configurations for which the total orbital angular momentum and the total spin angular momentum vanish. 

Cases in which there are three lone pairs, as in iodine(I) compounds, are better considered as being derived from closed shell configurations by the loss of electron density from one p orbital to the neighbouring atom. The quadrupole coupling constant then reflects the extent of electron transfer, and follows the electronegativity of the neighbour (Table 2.17). 

The coordination about a transition metal and the chemistry of transition metal complexes is often dictated by the electronic needs of the metal center. The stabilization of compounds when the elements present acquire a closed-shell configuration is well known. For a transition metal, with its nine valence orbitals (one s, five d, and three p orbitals), the stabilizing closed-shell configuration is obtained when the electron count about the metal center reaches 18. When a metal center has fewer than 18 electrons in its valence shell it is said to be electronically unsaturated. One step toward alleviating this electronic unsaturation is the formation of metal-metai bonds. Because of their covalent nature, metal-metal single bonds are considered to add one electron to the valence shell of each metal atom. The electron donation from one metal atom to the other mirrors the bond order so a quadruple bond increases the valence count of each metal by four electrons. 

Neon, with Z = 10, has the configuration [He]2s 2p, which completes the L shell. This closed-shell configuration is denoted [Ne] and acts as a core for subsequent elements. The next electron must enter the 3s orbital and begin a new shell, and so an Na atom, with Z = 11, has the configuration [Ne]3s . Like lithium with the configuration [He] 2s, sodium has a single s electron outside a complete core. 

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... 

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