Valence-electron hybridization

Traditional formula Covalent formula (valence-electron hybridization)... 

The formation of the same iron-oxygen covalent bonds from either (1) oxidized iron plus oxy anions via electron-transfer (redox) reactions or (2) radical-radical coupling reactions is summarized in Table 3-11. The valence-electron hybridization for the iron center is included as well as the spin state and estimated covalent bond-formation free energy (AGbf)- A similar set of reactions and data for iron-porphyrin compounds is presented in Table 3-12. Section a emphasizes that, just as the combination of a proton with a hydroxide ion yields a covalent H-OH bond (Table 3-11), (1) the combination of protons and porphyrin dianion (Por -) yields covalent porphine (H2Por), and (2) the addition of Lewis acids (Zn2+ or Fe2+) to porphine (H Por) oxidatively displaces protons to give covalent-bonded ZnilPor and Fe iPor. 

Table 3-11 Bonding and Valence-Electron Hybridization for Iron-Oxygen Compounds...

Fig. 30. 4f contribution to the photoelectron spectra of a series of Ce-based compounds. All these spectra were taken on the same instrument and the background of scattered electrons subtracted in the same fashion. These spectra are the difference between on-resonance and off-resonance spectra. They are ordered by increasing amount of 4f-valence electron hybridization from the bottom to the top (mote 7-Ce-like to more a-Uke). (After Allen et al 1986.)... 

The rapid rise of the hep-Sm-type phase boundary beyond Tm (fig. 123), and the anomalous high pressures of transformation in Y (hep - Sm-type, Sm-type dhep and dhep - fee) relative to lanthanide elements was cited by Gschneidner (1985b) as evidence for 4f valence electron hybridization having a significant role in determining the lanthanide crystal structure. He noted, however, that d occupation number probably is more important in determining which crystal structure would form, as had been proposed by others (e.g., see Duthie and Pettifor, 1977 Skriver, 1983). 

The term resonance has also been applied in valency. The general idea of resonance in this sense is that if the valency electrons in a molecule are capable of several alternative arrangements which differ by only a small amount in energy and have no geometrical differences, then the actual arrangement will be a hybrid of these various alternatives. See mesomerism. The stabilization of such a system over the non-resonating forms is the resonance energy. 

Trivalent ( classical carbenium ions contain an sp -hybridized electron-deficient carbon atom, which tends to be planar in the absence of constraining skeletal rigidity or steric interference. The carbenium carbon contains six valence electrons thus it is highly electron deficient. The structure of trivalent carbocations can always be adequately described by using only two-electron two-center bonds (Lewis valence bond structures). CH3 is the parent for trivalent ions. 

FIGURE 2 8 sp Hybridization (a) Electron configuration of carbon in its most stable state (b) Mixing the s orbital with the three p orbitals generates four sp hybrid orbitals The four sp hybrid orbitals are of equal energy therefore the four valence electrons are distributed evenly among them The axes of the four sp orbitals are directed toward the corners of a tetrahedron... 

The properties of tert butyl cation can be understood by focusing on its structure which IS shown m Figure 4 9 With only six valence electrons which are distributed among three coplanar ct bonds the positively charged carbon is sp hybridized The unhybridized 2p orbital that remains on the positively charged carbon contains no elec Irons Its axis is perpendicular to the plane of the bonds connecting that carbon to the three methyl groups... 

An estimate of the hybridization state of an atom in a molecule can be obtained from the group of the periodic table that the atom resides in (which describes the number of valence electrons) and the connectivity (coordination of the atom). The HyperChem default scheme uses this estimate to assign a hybridization state to all atoms from the set (null, s, sp, sp, sp -, and sp ). The special... 

If the number of valence electrons is 0 or 8, the hybridization is described as null. This is used for Group 0 (Inert gases). 

A second type of hybridisation of the valence electrons in the carbon atom can occur to form three 2sp hybrid orbitals leaving one unhybridised 2p orbital. 

In the third type of hybridisation of the valence electrons of carbon, two linear 2sp orbitals are formed leaving two unhybridised 2p orbitals. Linear a bonds are formed by overlap of the sp hybrid orbitals with orbitals of neighbouring atoms, as in the molecule ethyne (acetylene) C2H2, Fig. 1, A3. The unhybridised p orbitals of the carbon atoms overlap to form two n bonds the bonds formed between two C atoms in this way are represented as Csp Csp, or simply as C C. 

A great deal of evidence has shown that carbocations are planar. The divalent carbon is 5p2-hybridized, and the three substituents are oriented to the corners of an equilateral triangle, as indicated in Figure 6.9. Because there are only six valence electrons on carbon and all six are used in the three a bonds, the p orbital extending above and below the plane is unoccupied. 

The carbon-oxygen double bond of a carbonyl group is similar in many respects to the carbon-carbon double bond of an alkene. The carbonyl carbon atom is s/ 2-hybridized and forms three valence electron remains in a carbon p orbital and forms a tt bond to oxygen by overlap with an oxygen p orbital. The oxygen atom also has two nonbonding pairs of electrons, w hich occupy its remaining two orbitals. 

In the BeF2 molecule, there are two electron-pair bonds. These electron pairs are located in the two sp hybrid orbitals. In each orbital, one electron is a valence electron contributed by beryllium the other electron comes from the fluorine atom. 

Different Lewis structures do not in general make the same contribution to a resonance structure. It is possible to decide which structures are likely to make the major contribution by comparing the number of valence electrons distributed around each atom in a structure with the number of valence electrons on each of the free atoms. The smaller these differences for a structure, the greater is its contribution to a resonance hybrid. 

Saunders states. Assuming that the valence electrons at the top of the band have the average hybrid character 3d34s4p2, the interaction energy of one of these valence electrons and an atomic electron, assumed to be approximately a 3d electron, is found to be —2707 cm-, or —0.334 ev, with probable error about 10%. 

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