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PART - 1 CH - 4 Chemical Bonding and Molecular Structure — Chemistry STD 11 Science — Question

Rajasthan BoardEnglish MediumSTD 11 ScienceChemistryPART - 1 CH - 4 Chemical Bonding and Molecular Structure5 Marks
Question
Define octet rule. Write its significance and limitations.
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Answer

Octet Law (electronic principle of covalent bonding): While formation of bonds between atoms either electrons are transferred from one atom to another or sharing of electron takes place. In this atom completes its octet (eight electrons) of valence shell. This is known as octet law.
Octet law is mainly applicable on elements of second period and it is very useful to understand the structure of organic compounds. It has following exceptions:
(i) Incomplete octet of central atom (electron less than eight): In this the central atom have less than four valence electrons. Hence in compound total number of electrons around central atom is less than 8.
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(ii) Odd electron molecule: In these molecules odd number of electrons are present.
Example : $NO \left(15 e^{-}\right)$(nitric oxide), $NO _2\left(23 e^{-}\right)$ (nitrogen dioxide). In this all atom do not follow octet rule.
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(iii) Expand of Octet (Compound having more than 8 electrons on central metal atom): In this besides 3s and 3p. 3d orbital is also present to form bond. It occurs in third and next periods.
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(iv) Octet Law is based on chemical inertness of inert gases but some compounds of this can form.
Example : $XeF _2, KrF _2$ and $XeOF _2$, etc.
(v) It does not clear the shape of molecule.
(vi) It does not explain the stability and energy of molecule.

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