Chemical Bonding - Exceptions of Octet Rule-advanced

The Octet Rule, based on the electronic theory of chemical bonding, states that atoms tend to combine in such a way that they each have eight electrons in their valence shells, giving them the same electronic configuration as a noble gas ($ns^2 np^6$).

Incomplete Octet: In some compounds, the number of electrons surrounding the central atom is less than eight. This is common in elements with fewer than four valence electrons, such as $Li$, $Be$, and $B$. Examples include $LiCl$, $BeH_2$, and $BCl_3$.

Odd-Electron Molecules: In molecules with an odd number of electrons, like nitric oxide ($NO$) and nitrogen dioxide ($NO_2$), the octet rule cannot be satisfied for all atoms.

The Expanded Octet: Elements in and beyond the third period of the periodic table have $3d$ orbitals available for bonding. In compounds like $PCl_5$, $SF_6$, and $H_2SO_4$, the central atom has more than eight valence electrons.

Noble Gas Compounds: Although the octet rule is based on the chemical inertness of noble gases, some noble gases like Xenon ($Xe$) and Krypton ($Kr$) react with oxygen and fluorine to form compounds like $XeF_2$, $KrF_2$, and $XeOF_2$.

Formal Charge: It is the difference between the number of valence electrons in an isolated atom and the number of electrons assigned to that atom in a Lewis structure. It helps in determining the most stable structure when multiple Lewis structures are possible.