Question

state octet rule expain incomplete octet with suitable examples​

Answer 1

The octet rule is a chemical rule of thumb that reflects observation that atoms of main-group elements tend to bond in such a way that each atom has eight electrons in its valence shell, giving it the same electron configuration as a noble gas. 

There are certain atoms of certain elements that can exist in stable compounds forming bonds with less than eight valence electrons.  When this occurs, the atom of the element within the molecule is said to contain an incomplete octet. 

The common examples of such elements are hydrogen (stable with only 2 valence electrons), beryllium (stable with only 4 valence electrons) and boron and aluminum (stable with only 6 valence electrons).

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Answer 2

Answer :

Octet rule: Atoms of elements combine with each other in order to complete their respective octets so as to acquire the stable gas configuration.

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Significance: It helps to explain why different atoms combine with each other to form ionic compounds or covalent compounds.

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Limitations of Octet rule:

(1). According to Octet rule, atoms take part in chemical combination to achieve the configuration of nearest noble gas elements. However, some of noble gas elements like Xenon have formed compounds with fluorine and oxygen. For example: XeF2, XeF4 etc.

Therefore, validity of the octet rule has been challenged.

(2). This theory does not account for shape of molecules.