Valence bond theory hybridization of atomic orbitals

We also superimpose paired half-arrows in the filled sulfur i and p orbitals to represent the lone pair electrons in those orbitals. (Since those orbitals are full, they are not involved in bonding.) 

The answer to the question What is a chemical bond depends on the bonding model. Answer these three questions  

7 Valence Bond Theory Hybridization of Atomic Orbitals 

Although the overlap of half-filled standard atomic orbitals adequately explains the bonding in H2S, it cannot adequately explain the bonding in many other molecules. For example, suppose we try to explain the bonding between hydrogen and carbon using the same approach. The valence electron configurations of H and C are as follows  

Carbon has only two half-filled orbitals and should therefore form only two bonds with two hydrogen atoms. We would therefore predict that carbon and hydrogen should form a molecule with the formula CH2 and with a bond angle of 90° (corresponding to the angle between any two p orbitals). 

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Valence bond theory hybridization of atomic orbitals... 

Valence Bond Theory Hybridization of Atomic Orbitals 447 Formation of sp Hybrid Orbitals... 

Valence Shell Electron Pair Repulsion (VSEPR) Theory Hybridization of Atomic Orbitals, sp, sp, sp Single Bonds Conformational Isomers Pi Bonds Pi Barrier to Rotation C/s and Trans, 2p-3p Triple Bonds Cumulenes... 

Table 5.1 also includes the types of hybridization for each of the basic shapes which are used in VSEPR and valence bond theories. Hybridization, or mixing of the indicated atomic orbitals, in each case produces hybrid orbitals that radiate from the central atom to where the ligand atoms are situated. This is done to ensure that there are localized... 

The Fermi hole for the reference electron at a bonded maxima in the VSCC of the carbon atom has the appearance of the density of a directed sp hybrid orbital of valence bond theory or of the density of a localized bonding orbital of molecular orbital theory. Luken (1982, 1984) has also discussed and illustrated the properties of the Fermi hole and noted the similarity in appearance of the density of a Fermi hole to that for a corresponding localized molecular orbital. We emphasize here again that localized orbitals like the Fermi holes shown above for valence electrons are, in general, not sufficiently localized to separate regions of space to correspond to physically localized or distinct electron pairs. The fact that the Fermi hole resembles localized orbitals in systems where physical localization of pairs is not found further illustrates this point. 

There are two quantum mechanical explanations for covalent bond formation valence bond theory and molecular orbital theory. In valence bond theory, hybridized atomic orbitals are formed by the combination and rearrangement of orbitals from the same atom. The hybridized orbitals are aU of equal energy and electron density, and the number of hybridized orbitals is equal to the number of pure atomic orbitals that combine. 

According to valence bond theory, the C atom is described as sp hybridized, and it forms one sigma bond with each of the three O atoms. This leaves one unhybridized 2p atomic orbital on the C atom, say the 2p orbital. This orbital is capable of overlapping and mixing with the 2p orbital of any of the three O atoms. The sharing of two electrons in the resulting localized pi orbital would form a pi bond. Thus, three equivalent resonance structures can be drawn in valence bond terms (Figure 9-10b). We emphasize that there is no evidence for the existence of these separate resonance structures. 

It is useflil to show the valence bond representations of the complexes [CoFe] and [Co(NH3)6], which can then be compared with representations from the crystal field and molecular orbital theories to be discussed later. First, we must know from experiment that [CoF ] contains four unpaired electrons, whereas [Co(NH3)g] has all of its electrons paired. Each of the ligands, as Lewis bases, contributes a pair of electrons to form a coordinate covalent bond. The valence bond theory designations of the electronic structures are shown in Figure 2.7. The bonding is described as being covalent. Appropriate combinations of metal atomic orbitals are blended together to give a new set of orbitals, called hybrid orbitals. 

Dipole Moments 322 Valence Bond Theory 325 Hybridization of Atomic Orbitals 328... 

Using valence bond theory, each of the four bonds in methane is represented by the overlap between an ry> -hybridized atomic orbital from the carbon atom and an s orbital from a hydrogen atom (Figure 1.23). For purposes of clarity the back lobes (blue) have been omitted from the images in Figure 1.23. 

It is important to appreciate clearly the distinction between SC theory and the older or classical valence bond theory. In classical VB theory, the orbitals are taken to be predetermined, either as simple atomic orbitals or hybrids of atomic orbitals. These hybrids, moreover, are fixed, for example, either as sp, sp, or sp, etc., -type orbitals. In SC theory, in contrast, no such preconceptions are imposed. The orbitals are optimized as linear combinations of basis functions (usually approximate AOs) much as in MO-based approaches. However, in common with classical VB theory, the SC orbitals in general overlap with one another (except, of course, in the case of orbitals of different symmetry), or, since the SC orbitals are often localized, by virtue of the physical separation between them. Generally speaking no constraints, apart from normalization, are applied to the SC orbitals and as a result they may be as localized or as delocalized as the situation demands. Bearing in mind that the SC orbitals are always singly occupied, this last means that their shapes are determined by whatever produces the optimum balance between the greatest extent of avoidance of the electrons in different orbitals and quantum interference effects, which arise from the overlap between orbitals. In practice, we have found that this invariably means that the SC orbitals turn out to be localized and indeed often resemble atomic or hybrid atomic orbitals, or semi-localized, meaning that the SC orbitals spread over two or, at most, three centres. 

Strength The hybridization of atomic orbitals is not a separate bonding theory rather, it is an extension of valence bond theory. Using hybrid orbitals, we can understand the bonding and geometry of more molecules, including BeCl2, BF3, and CH4. 

Describe the molecular geometry of H2O suggested by each of the following methods (a) Lewis theory (b) valence bond method using simple atomic orbitals (c) VSEPR theory (d) valence bond method using hybridized atomic orbitals. 

Valence bond theory (Section 2 3) Theory of chemical bond mg based on overlap of half filled atomic orbitals between two atoms Orbital hybridization is an important element of valence bond theory... 

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