Vacant atomic orbital

Electron-donating orbitals are those occupied by electrons, i.e., bonding orbitals of bonds, non-bonding orbitals of lone pairs, HOMOs of molecnles, gronps and others. Electron-accepting orbitals are vacant orbitals, i.e., antibonding orbitals of bonds, vacant atomic orbitals on cationic centers, LUMOs of molecnles, gronps, etc. 

Both saturated and unsaturated organic compounds have been found to be good quenchers. In many cases, H atom abstraction may be a very probable mechanism. In others, some form of association involving donation jo --electrons into vacant atomic orbital of mercury seems likely. There is also the possibility of energy transfer to the triplet level of the quencher. 

The organometallic compounds most likely to undergo hydrolysis are those with ionic bonds, those with relatively polar covalent bonds, and those with vacant atomic orbitals (see Chapter 1) on the metal atom, which can accept more electrons. These provide sites of attack for the water molecules. For example, liquid trimethylaluminum reacts almost explosively with water or water and air ... 

Population of vacant atomic orbitals and electron density distribution... 

It is instructive to study the vacant atomic orbital population in dimers and trimers. As mentioned in the Introduction, in the 80 s Bauschlicher et al. [10,11] came to the conclusion that the promotion of ns-electrons to np-orbitals leading to sp-hybridization is the main mechanism responsible for binding in alkaline-earth clusters. This conclusion was based on a study of the SCF Mulliken population analysis for tetramers, which are stable at the SCF level. At present, we can perform more precise analysis using the Natural Bond Orbital Analysis and calculate it at the electron correlation level. 

It is important to check is the effect of a rather large population of vacant atomic orbitals at the electron correlation level specific for alkaline-earth atoms or it has a general character. In Table VII we present the results of net valence population calculations for noble-gas atoms performed by the Natural Bond Orbital Analysis at the MP4 level. We found non-negligible valence orbital population, especially for the d-orbitals. The results obtained for three different basis sets are quite close. Thus, the population of vacant orbitals in noble-gas atoms is not an artifact of the calculations. From this follows that elements traditionally assumed as closed-shell (noble gases) or closed-subshell (alkaline earths) atoms can to some extent manifest an anisotropic p-or d-symmetry behavior. It would be very interesting to obtain experimental evidence confirming this theoretical prediction. 

The formation of a coordinate complex of a metal ion arises from the tendency of the ion to acquire a stable electronic configuration by filling up its vacant atomic orbitals by electrons which the ligand makes available. The coordination complex obtained may be an uncharged or a charged species. 

Solution Electrophilic reagents are species with a deficiency of electrons, e.g. a vacant atomic orbital. 

Perhaps you will not be surprised, then, you to learn that an even more general model of acids and bases was proposed by American chemist G. N. Lewis (1875-1946). Recall that Lewis developed the electron-pair theory of chemical bonding and introduced Lewis structures to keep track of the electrons in atoms and molecules. He applied his electron-pair theory of chemical bonding to acid-base reactions. Lewis proposed that an acid is an ion or molecule with a vacant atomic orbital that can accept (share) an electron pair. A base is an ion or molecule with a lone electron pair that it can donate (share). According to the Lewis model, a Lewis acid is an electron-pair acceptor and a Lewis base is an electron-pair donor. Note that the Lewis model includes all the substances classified as Bronsted-Lowry acids and bases and many more. 

Before discussing the photoelectrochemical cells, a brief review of the nature of semiconductors is perhaps desirable. The electronic properties of solids can be described in terms of a band model which treats the behavior of electrons moving in the field of the atomic nuclei. When a solid is formed, the isolated atoms, which are characterized by filled and vacant atomic orbitals are assembled into a lattice containing about 5 X 10 atoms cm This leads to the formation of new molecular orbitals which are so closely spaced that they form essentially continuous bands. 

The crystal orbitals were calculated by the DFT method in the plane-wave basis set with the CASTEP code [377] in the GGA density functional. A set of special points k in the Brillouin zone for all the crystals was generated by the snperceU method (see Chap. 3) with a 5 x 5 x 5 diagonal symmetric extension, which corresponds to 125 points. In all cases, the pseudopotentials were represented by the normconserving optimized atomic pseudopotentials [621], which were also used to calculate the atomic potentials of free atoms. In the framework of both techniques (A, B), the population analysis was performed in the minimal atomic basis set i.e. the basis set involved only occupied or partially occupied atomic orbitals of free atoms. It is well known that the inclusion of diffuse vacant atomic orbitals in the basis set can substantially change the results of the population analysis. For example, if the Mg 2p vacant atomic orbitals are included in the basis set, the charge calculated by technique A for the Mg... 

When r = 0, 4r component represents a vacant atomic orbital and if q = 0, (4g+2) component is treated as an atomic orbital occupied by two electrons. A single atomic orbital is represented by Greek letter (D(omega) Vs o-and... 

---