Exceptions to the Octet Rule
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.