Phosphorus, octet rule exceptions

The octet rule accounts for the valences of many of the elements and the structures of many compounds. Carbon, nitrogen, oxygen, and fluorine obey the octet rule rigorously, provided there are enough electrons to go around. However, some compounds have an odd number of electrons. In addition, an atom of phosphorus, sulfur, chlorine, or another nonmetal in Period 3 and subsequent periods can accommodate more than eight electrons in its valence shell. The following two sections show how to recognize exceptions to the octet rule. 

Most of the common elements in organic compounds—C, N, O, and the halogens— follow the octet rule. Hydrogen is a notable exception, because it accommodates only two electrons in bonding. Additional exceptions include boron and beryllium (second-row elements in groups 3A and 2A, respectively), and elements in the third row (particularly phosphorus and sulfur). 

A second exception to the octet rule occurs with some elements located in the third row and later in the periodic table. These elements have empty d orbitals available to accept electrons, and thus they may have more than eight electrons around them. For organic chemists, the two most common elements in this category are phosphorus and sulfur, which can have 10 or even 12 electrons around them. Examples of these phosphorus and sulfur compounds include the following ... 

The species PF5, PFg, SFg are exceptions to the octet rule. In PF5 there are ten electrons in the valency group around the phosphorus atom in PF and SFg there are twelve electrons in the valency groups. The elements in the first row, on the other hand, are bound rigidly to the rule of eight. ... 

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