Define octet rule. Write its significance and limitations



Octet rule: Atoms can combine either by transfer of valence electrons from one atom to another (gaining or loosing) or by sharing of valence electrons in order to have an octet in their valence shells. Significance : Occuring 8 electrons (octet formation) in the valence shells of atoms leads to stable electronic configuration.Define octet rule. Write its significance and limitations.
Noble gases (except He) have 8 electrons in their valence shells and are generally not reactive. Limitations: (i) Formations of compounds involving hydrogen : Hydrogen atom has only one electron in its valence shell, it needs one more electron to acquire the nearest noble gas configuration of Helium. Hence hydrogen needs to complete its duplet (acquiring 2 electrons in its valence shell) rather than octet.
(ii) Formation of compounds like Be$C{{l}{2}}$ B${{F}{3}}$, Al$C{{l}{3}}$ : In each of these examples central atom Be in Be$C{{l}{2}}$, B in B${{F}{3}}$ and Al in Al$C{{l}{3}}$ has less than 8 electrons i.e.,these compounds are electron

(iv) Formation of compounds of noble gases: Noble gases on which octet rule is based have already 8 electrons in their valence shells and should not form compounds.
Odd electron bonds/Odd electron molecules:
There are certain molecules and ions like NO, and ${{O}_{2}}$ in which the bonded atoms contain odd number of electrons between them.