Bonding Models in Inorganic Chemistry 2. The Covalent Bond

Bonding Models in Inorganic Chemistry 2. The Covalent Bond 

This chapter and the one following will be devoted to a preliminary analysis of covalent bonding. Most or the ideas presented here may be found elsewhere and with greater rigor, and many will have been encountered in previous courses. However, since they form the basis for subsequent chapters, a brief presentation is in order here. Covalent bonding will also be discussed in Chapters 6 and 11. 

Normally two electrons pair up to form each bond. This is a consequence of the Pauli exclusion principle—two electrons must have paired spins if they are both to occupy the same region of space between the nuclei and thereby attract both nuclei. The definition of a bond as a shared pair of electrons, however, is overly restrictive, and we shall see that the early emphasis on electron pairing in bond formation is unnecessary and even misleading. 

For most atoms there will be a maximum of eight electrons in the valence shell =Lewis octet structure). This is absolutely necessary for atoms of the elements lithium through fluorine since they have only four orbitals (an s and three p orbitals) in Ihe valence shell. It is quite common, as well, for atoms of other elements to utilize only their s and p orbitals. Under these conditions the sum of shared pairs (bonds) and unshared pairs (lone pairs) must equal the number of orbitals—four. This is Ihe maximum, and for elements having fewer than four valence electrons, the octet will usually not be filled. The following compounds illustrate these possibilities  

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