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Valence bond treatment of

Historically, molecular orbital theory was preceded by an alternative and successful description of the bonding in H2. In 1927, W. Heitler and F. London proposed the valence bond theory, in which each electron resides in an atomic orbital. In other words, in this model, the identity of the atomic orbital is preserved. There are two ways in which the two electrons in H2 can be accommodated in the pair of Is atomic orbitals  [Pg.86]

The valence bond wavefunction for H2 is simply a linear combination of in [Pg.86]

Upon solving for E, we substitute E into the following secular equations to obtain coefficient c and cn  [Pg.86]

A diagram illustrating the various distances in H2 is shown in Fig. 3.2.1. The Hamiltonian operator for this system, in a.u., is [Pg.87]

When we plot E+ and E- against rab, we get the energy curves shown in Fig. 3.2.2. So, once again, the valence bond treatment yields a stable H2 molecule, even though the quantitative results do not match exactly the experimental data. [Pg.88]


What happens when we have a many-electron wavefunction, such as the one below which relates to the simple valence-bond treatment of dihydrogen ... [Pg.100]

Herzberg (Nobel prize for Chemistry, 1971) commented on the two distinct photoionizations from methane that this observation illustrates the rather drastic nature of the approximation made in the valence bond treatment of CH4, in which the 2s and 2p electrons of the carbon atom are considered as degenerate and where this degeneracy is used to form tetrahedral orbitals representing mixtures of 2s and 2p atomic orbitals. The molecular orbital treatment does not have this difficulty". [Pg.125]

Pauling150 has provided an alternative, valence bond treatment of the quadruple bond involving spd hybrid orbitals and four equivalent bent bonds. His model also explains the experimental facts described above and provides a good estimate of the bond length. [Pg.941]

The results of a valence bond treatment of the rotational barrier in ethane lie between the extremes of the NBO and EDA analyses and seem to reconcile this dispute by suggesting that both Pauli repulsion and hyperconjugation are important. This is probably closest to the truth (remember that Pauli repulsion dominates in the higher alkanes) but the VB approach is still imperfect and also is mostly a very powerful expert method [43]. VB methods construct the total wave function from linear combinations of covalent resonance and an array of ionic structures as the covalent structure is typically much lower in energy, the ionic contributions are included by using highly delocalised (and polarisable) so-called Coulson-Fischer orbitals. Needless to say, this is not error free and the brief description of this rather old but valuable approach indicates the expert nature of this type of analysis. [Pg.187]

After a simple valence bond treatment of H2, we now proceed to study the excited states of H2. Through this discussion, we will recognize that the molecular orbital and valence bond treatments, after modification, can bring about the same quantitative results. [Pg.88]

I used these tables of Preul for the first part of my doctoral work. The computation of integrals for a valence bond treatment of the H-F molecule on a mechanical desk calculator was greatly simplified by the fact that I could look up values for the required auxiliary functions in these tables. Toward the end of this work (1962-1963), I got access to the electronic computer Z23, which of course could perform the calculations in a much shorter time with much higher accuracy. [Pg.266]

Figure 4.3 Valence bond treatment of singlet and triplet states... Figure 4.3 Valence bond treatment of singlet and triplet states...
As an alternative to attempting to approximate all the terms arising in the simple valence-bond treatment of H3, we can make the rather drastic, but traditional, approximation of assuming orthogonal orbitals. This leads to an energy expression for the lowest electronic state of H3 of the form ... [Pg.166]

The application of the (8—n) rule to elements preceding group 4 implies the availability of (8—n) electrons per atom for covalent bond formation and is to this extent artificial unless a mechanism for the provision of these electrons can be proposed. A possible mechanism in the case of zinc, based on the valence-bond treatment of metal theory, has already been outlined in 5.28, but it is difficult to feel satisfied that this is more than an ad hoc explanation designed to explain the observed crystal structure of the element if the structure of zinc were unknown there would be few grounds for treating it as other than a simple divalent element. [Pg.133]

Worked example 4.2 Valence bond treatment of the bonding in [NO3]... [Pg.106]

Let us compare the molecular-orbital and valence-bond treatments of the H2 ground state. [Pg.414]

The valence-bond treatment of polyatomic molecules is closely tied to chemical ideas of structure. One begins with the atoms that form the molecule and pairs up the unpaired electrons to form chemical bonds. There are usually several ways of pairing up (coupling) the electrons. Each pairing scheme gives a VB structure. A Heitler-London-type function (called a bond eigenfunction) is written for each structure i, and the molecular wave function is taken as a linear combination 2, c,4>, of the bond eigenfunctions. The variation principle is then applied to determine the coefficients c,. The VB wave function is said to be a resonance hybrid of the various structures. [Pg.604]

Section 15.24 Valence-Bond Treatment of Polyatomic Molecules 605... [Pg.605]


See other pages where Valence bond treatment of is mentioned: [Pg.94]    [Pg.3]    [Pg.94]    [Pg.93]    [Pg.121]    [Pg.101]    [Pg.86]    [Pg.537]    [Pg.288]    [Pg.190]    [Pg.190]    [Pg.704]    [Pg.130]    [Pg.43]    [Pg.169]    [Pg.34]    [Pg.43]    [Pg.121]    [Pg.193]    [Pg.410]    [Pg.411]    [Pg.413]    [Pg.604]   


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Valence-bond treatment

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