Orbitals Molecular Orbital and Valence Bond Models

Orbitals Molecular Orbital and Valence Bond Models 

The bonding schemes in the rest of this book rarely rely on orbital methods, and orbitals are reviewed in this section only because they are always used in qualitative discussions of bonding in the chemical literature. This being the case, some familiarity with the relevant terminology is convenient for one to be comfortable with the literature and be able to translate arguments based on orbitals to arguments based on localized valence electrons, as are used in the remainder of this book. Orbital models are discussed extensively in most chemistry texts. 

If models are works of fiction, the molecular orbital (MO) model is an epic novel. The MO model is almost the only model for the chemical bond that is generally used in academic physics and chemistry for a good reason it describes certain features of covalent bonding quite well if sufficient computer capability is available and if the structure of the molecule is known. In simple molecules the 

The VB model given by Heitler and London was the first description of covalent bonding that followed the formulation of quantum mechanics. If (1) and (j b(2) are the one-electron wavefunctions or orbitals localized on neighboring atoms labeled a and b (e.g., the Is-orbitals on the two hydrogen atoms labeled a and b in molecular hydrogen) and each is occupied by one electron (the numbers 1 and 2 represent the coordinates of the two electrons and stand for x, z, X2, 2  

The factor normalizes the VB wavefunction in order to get the right total probabilities for finding electrons anywhere in space when they are described by this function. 

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