What is Octet Rule?
The tendency of atoms to have 8 electrons in their outermost shell is known as the Octet Rule or Rule of Eight. The octet rule describes that an atom’s preference for having eight electrons in its valence shell.
Exceptions to the Octet Rule:
i. An ion, atom, or a molecule containing an unpaired valence electron is called a free radical. These species disobey the octet rule. However, they are very unstable and tend to spontaneously dimerize.
ii. Aromatic compounds involve a de-localization of pi electrons. These electrons obey Huckel’s rule
iii. The first shell can only accommodate two electrons, elements such as lithium, helium, and hydrogen obey the duet rule instead of the octet rule.
iv. Due to the presence of a d-orbital, the transition elements do not obey the octet rule. The valence shells of these atoms can hold 18 electrons.