Question

Explain why $AsF_5$ does not octet rule? how/why are there exceptions to the octet rule?

Answer 1

Arsenic has an inert gas arrangement of: $\left[ {Ar} \right]4{s^2}3{d^{10}}4{p^3}$. Since arsenic has $n = 4$, at that point it has rakish energy quantum numbers in this shell of $0$, $1$, $2$, $3$, so you'd never compose the electron arrangement like this, $\left[ {Ar} \right]4{s^2}3{d^{10}}4{p^3}4{d^0}4{f^0}$, yet this shows that since $n = 4$, there is a void orbital $4d$.

Complete step by step answer:
I clarify this in class once in a while like "since your structure has a fourth floor, at that point that implies it has a room called $s$, and $p$, and $d$, and $f$,there is no one in the $d$ or $f$ room, yet they are still there…just void"
Essentially these unfilled $d$ orbitals can engage in the hybridization cycle ($s{p^3}{d^1}$,$s{p^3}{d^2}$) to permit these focal molecules to have an expanded octet.
The octet decides states that particles with a nuclear number under $20$ will in general consolidate so they each have eight electrons in their valence shells, which gives them a similar electronic setup as an inert gas. It clung to five fluorine iotas, giving it $10$ electrons, which is in excess of an octet.
The two components that most ordinarily neglect to finish an octet are boron and aluminium; the two of them promptly structure mixes in which they have six valence electrons, instead of the typical eight anticipated by the octet rule.
While particles exist that contain molecules with less than eight valence electrons, these mixes are regularly responsive and can respond to frame species with eight valence electrons. For instance, $B{F_3}$ will promptly tie a fluoride anion to frame the $B{F_4}$–anion, in which boron observes the octet rule.
The octet states that particles underneath nuclear number $20$ will in general consolidate so they each have eight electrons in their valence shells, which gives them similar electronic arrangement as an honourable gas. The standard is relevant to the principal bunch components, particularly carbon, nitrogen, oxygen, and the incandescent lamp, yet in addition to metals, for example, sodium and magnesium. Valence electrons can be tallied utilizing a Lewis electron dot structure. In carbon dioxide, for instance, every oxygen imparts four electrons to the focal carbon.

Note:
Although the octet rule can even now be of some utility in understanding the science of boron and aluminium the mixes of these components are more enthusiastically anticipated than for different components.