Question

what are the limitations of octet rule?

Answer 1

Answer:

Octet rule fails to explain the following:

(1) The stability of incomplete octet molecules, i.e., the molecules with the central atom containing less than eight electrons.

For example, $\sf{BeCl_2}, {BF_3}$.

(2) The stability of expanded octet molecules, i.e., the molecules with the central atom containing more than eight electrons.

For example, $\sf{PC_5}, {SF_6}$.

(3) Observed shape and geometry of the molecules.

(4) Difference in energies and reactivities of different molecules.

Answer 2

There are mainly three limitations of the octet rule

• According to the octet rule 'If the outermost shell of an atom has 8 electrons then it will be stable.
• Stable atoms will be inert.
• It was successful in explaining bonding in the compounds.
• But there were some limitations as well
• 1) Incomplete octet of the central atom
• Consider compounds like BeH₂, LiCl, BF₃, etc.
• The central atom is lacking eight electrons.
• But still, these compounds are stable and they do exist.
• 2) Odd electron molecules
• NO and NO₂ have 15 and 23 electrons respectively.
• They do not obey the octet rule but do exist
• 3) Expanded atoms
• Consider compounds like PF₅, SF₆
• The central atom has more than 8 electrons and is stable
• Octet rule fails in the above three cases
• #SPJ3