Standard Valence-Bond Theory and

Chapter 2 Pauling 3-Electron Bonds , 4-Electron 3-Centre Bonding, and the Need. .. 

Two different bonding indiees will be used in this book, namely bond-number and bond-order. The bond number refers to the number of pairs of electrons that form a covalent bond. It may be calculated from the weights of the valence-bond structures that are used to describe the electronic structure of the molecule, as is demonstrated above for N2O. The bond-order is a molecular orbital index of bonding. For the purpose of qualitative discussion of diatomic bonding, we shall define the bond-order to be /4 (No. of bonding electrons) - (No. of antibonding electrons). Another definition of bond-order will be introduced in Chapter 14. 

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