Question

Why does the octet rule have exceptions?

Answer 1

The octet rule is a chemical rule of thumb that represents the hypothesis that main-group elements tend to bind in such a way that each atom has eight electrons in its valence shell, resulting in an electronic configuration similar to that of a noble gas.

Complete answer:
A molecule or an ion having at least one atom with more than an octet of electrons is the most prevalent exception to the octet rule. Period 3 and beyond elements have such complexes. $S{{F}_{6}}$, a material used in the electric power sector to insulate high-voltage lines, and the $S{{O}_{4}}^{2-}~$ and $P{{O}_{4}}^{3-}$ ions are examples of p-block elements.
Consider the Lewis structure of sulphur hexafluoride ($S{{F}_{6}}$), which must accept a total of 48 valence electrons [$\text{6 + }\left( \text{6 x 7} \right)\text{ = 48}$]. When the atoms and electrons are arranged symmetrically, we get a structure with six bonds to sulphur, or a six-coordinate structure. Although each fluorine atom has an octet, the sulphur atom has 12 rather than 8 electrons around it. When an atom is linked to more than four other atoms, the third stage in our method for creating Lewis electron structures, in which we insert an electron pair between each pair of bonded atoms, must have more than eight electrons.
The octet rule is based on the fact that each valence orbital can only hold two electrons (usually one ns and three np orbitals). Sulfur must use not just the ns and np valence orbitals, but also extra orbitals to accommodate more than eight electrons. Because sulphur has an electron configuration of $\left[ Ne \right]3{{s}^{2}}3{{p}^{4}}3{{d}^{0}}$ , it could theoretically accept more than eight valence electrons by utilising one or more d orbitals. As a result, species like $S{{F}_{6}}$ are frequently referred to as expanded-valence molecules. Although it is debatable whether such compounds employ d orbitals in bonding, this hypothesis explains why compounds with more than an octet of electrons surrounding an atom occur.

Note:
There is no link between a molecule's or ion's stability and whether or not it has an enlarged valence shell. Some species with enlarged valences are extremely reactive, whereas others, such as $S{{F}_{6}}$ , are not. In fact, $S{{F}_{6}}$ is so inert that it has a wide range of economic uses. It is employed as a coolant in some nuclear power reactors and as the pressurising gas in “unpressurized” tennis balls, in addition to being an electrical insulator.