Question

State octet rule.

Answer 1

The octet rule explains the chemical bonding in various chemical compounds. It illustrates different bonds like covalent bond, electrovalent bond, and coordinate bond.

Complete step by step answer:
The octet rule states that every atom binds to another atom by donating or accepting electrons to have eight electrons in its valence shell.
According to the octet rule, an atom having eight electrons in its valence shell is said to be a complete atom.
Atoms that have incomplete orbitals accept electrons and complete the valence shell and thus, fulfil octet rule.
The significance of octet rule is that it explains the formation and stability of various compounds.
The limitations of octet rule are that the octet rule is not universal because it applies to most organic compounds and to the elements of the second period of the periodic table.

Additional Information: The exceptions of octet rule are as follows:
Incomplete octet of the central atom:
In some compounds, the electrons surrounding the central atom are less than eight. This is for the elements that have less than four valence electrons.
Examples: ${\text{LiCl}}$, ${\text{Be}}{{\text{H}}_{\text{2}}}$ and ${\text{BC}}{{\text{l}}_{\text{3}}}$. This is because the boron, lithium, beryllium and boron have 1, 2 and 3 valence electrons respectively.
Odd-electron molecules:
Some atoms in molecules have an odd number of electrons.
Examples: ${\text{NO}}$, ${\text{N}}{{\text{O}}_2}$.
Expanded octet:
The elements in and beyond the third period of periodic table have 3d orbitals available for bonding. They have more than eight electrons around the central atom. This is known as expanded octet.

Note:
Other drawbacks of octet rule are as follows:
The octet rule is based on the chemically inert nature of the noble gases.
The octet rule does not take into account the shape of the molecule.