Bonds valence bond theory

The Nature of Chemical Bonds Valence Bond Theory... 

How does electron sharing lead to bonding between atoms Two models have been developed to describe covalent bonding valence bond theory and molecular orbital theory. Each model has its strengths and weaknesses, and chemists tend... 

We said in Section 1.5 that chemists use two models for describing covalent bonds valence bond theory and molecular orbital theory. Having now seen the valence bond approach, which uses hybrid atomic orbitals to account for geometry and assumes the overlap of atomic orbitals to account for electron sharing, let s look briefly at the molecular orbital approach to bonding. We ll return to the topic in Chapters 14 and 15 for a more in-depth discussion. 

Lewis s theory of the chemical bond was brilliant, but it was little more than guesswork inspired by insight. Lewis had no way of knowing why an electron pair was so important for the formation of covalent bonds. Valence-bond theory explained the importance of the electron pair in terms of spin-pairing but it could not explain the properties of some molecules. Molecular orbital theory, which is also based on quantum mechanics and was introduced in the late 1920s by Mul-liken and Hund, has proved to be the most successful theory of the chemical bond it overcomes all the deficiencies of Lewis s theory and is easier to use in calculations than valence-bond theory. 

Consider the trigonal planar carbonate ion, C03 , as an example. All the carbon-oxygen bonds in the ion have the same bond length and the same energy, intermediate between those of typical C—O and C=0 bonds. Valence bond theory describes the ion in terms of three contributing resonance structures (Figure 9-10a). No one of the three resonance forms adequately describes the bonding. 

It is in the realm of cupric square planar complexes where the valence bond theory gives not only an inadequate, but an incorrect description of the bonding. Valence bond theory ignores the presence of antibonding orbitals and invokes the use of a linear combination of d -y, Px, Py, and s orbitals to form the a bonds. For d ions, the ninth electron can only... 

Resonance between imaginary structures having localised bond (valence bond theory) or delocalization of it orbitals (molecular orbital theory) have both been found to explain the bonding state of benzene. The benzene molecule may be represented either as a hybrid of Kekule structures (valence bond theory) or as a regular carbon hexagon having an inscribed circle or dotted circle that symbolizes the three delocalized n orbitals. 

In this chapter we discuss how you explain the geometries of molecules in terms of their electronic structures. We also explore two theories of chemical bonding valence bond theory and molecular orbital theory. 

THE NATURE OF CHEMICAL BONDS VALENCE BOND THEORY... 

Atomic Structure The Nucleus Atomic Structure Orbitals 4 Atomic Structure Electron Configurations 6 Development of Chemical Bonding Theory 7 The Nature of Chemical Bonds Valence Bond Theory sp Hybrid Orbitals and the Structure of Methane 12 sp Hybrid Orbitals and the Structure of Ethane 13 sp2 Hybrid Orbitals and the Structure of Ethylene 14 sp Hybrid Orbitals and the Structure of Acetylene 17 Hybridization of Nitrogen, Oxygen, Phosphorus, and Sulfur 18 The Nature of Chemical Bonds Molecular Orbital Theory 20 Drawing Chemical Structures 21 Summary 24... 

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