Question

Write the significance and limitations of the octet rule.

Answer 1

This question is simple to answer. Just explain a little bit about what is an octet rule. Then write its significance and at last its limitations. It will be better if you provide some examples to explain the limitations to help understand in a better manner.

Complete answer:
The octet rule refers to the tendency of atoms to prefer to have eight electrons in the valence shell. When atoms have fewer than eight electrons, they tend to react and form more stable compounds. It states that atoms tend to form compounds in ways that give them eight valence electrons and thus the electron configuration of a noble gas. Compounds satisfy the octet rules in two ways, either by sharing several coordination electrons or by the complete transfer of electrons.
Significance of octet rule:
The octet rule can explain chemical bonding in various compounds
It illustrates the various types of bonds like a covalent bond, electrovalent bond and coordinate bond.
It explains the stability of the compounds.
Limitations of octet rule:
Incomplete octet of the central metal atom- in some compounds, the number of electrons surrounding the central atom is less than the eight electrons. Example-Li, Be, and Boron have $1,{\text{ }}2,{\text{ }}and{\text{ }}3$ valence electrons only.
Odd electron molecule- in molecules with odd numbers of electrons like nitric oxide $(NO)$ and nitrogen dioxide$(N{O_2})$ the octet rule is not satisfied for all the atoms.
The expanded octet: In several compounds of elements in ${3^{rd}}$ period of the periodic table, there are more than eight valence electrons around the central atom. This is termed the expanded octet. The octet rule does not apply in such cases. Some of the examples of such compounds are: $P{F_5},{\text{ }}S{F_6},{\text{ }}{H_2}S{O_4}$ and a number of coordination compounds.

Note:
The octet rule was given by German chemist Walther Kossel and the American chemist Gilbert Newton Lewis. It is only applicable to the main group elements. There are many more molecules that do not obey the octet rule. Not every molecule or an atom needs to obey the rule; there can be exceptions and drawbacks.