Explain the Octet rule. Mention its limitations.

The Octet Rule states that atoms tend to gain, lose, or share electrons in order to have eight electrons in their valence shell (outermost electron shell), achieving a stable electron configuration similar to that of a noble gas. This stability is associated with a lower energy state.

Limitations:

• Incomplete octets: Some elements, particularly those in the second period (like Be and B), are stable with fewer than eight electrons.
• Expanded octets: Elements in the third period and beyond can have more than eight electrons in their valence shell, forming hypervalent molecules (e.g., PCl₅, SF₆).
• Odd-electron molecules: Molecules with an odd number of electrons (e.g., NO) cannot satisfy the octet rule for all atoms.
• Transition metals: Transition metals often do not follow the octet rule, using d and f orbitals in bonding.