How can the octet rule be violated?

1 Answer
Feb 14, 2014

The octet rule is violated whenever a bonded atom has either fewer or more than eight valence electrons in its valence shell.

INCOMPLETE OCTET

BH₃ has only six valence electrons around B. The B atom has an incomplete octet.

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ODD-ELECTRON MOLECULES

Nitrogen monoxide, NO, has 11 valence electrons. There is no way that both atoms can get an octet. One atom is always stuck with only 7 electrons in its valence shell.

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FREE RADICALS

Free radicals are reactive intermediates that are formed during reactions, for example, by removing an H atom with its shared electron from a molecule such as CH₄. They have incomplete octets and unpaired electrons.

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EXPANDED OCTETS

The nonmetals after silicon in the Periodic Table can “expand their octet” and have more than eight valence electrons around the central atom. An example is PF₅, with 10 electrons in its valence shell.

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