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 Limitations of the lewis structures??..! :) :D

Lewis formulas are misleading in the sense that atoms and electrons are shown as being static. By being essentially two-dimensional representations they also fail to give an accurate idea of the three-dimensional features of the molecule, such as actual bond angles and topography of the molecular frame.

For example a given compound can have several valid Lewis formulas. For example CH3CNO can be represented by at least three different but valid Lewis structures called resonance forms, or resonance structures, shown below.

 

 

 

However, a stable compound such as the above does not exist in multiple states represented by structures I, or II, or III. The compound exists in a single state called a hybrid of all three structures. That is, it contains contributions of all three resonance forms, much like a person might have physical features inherited from each parent to varying degrees.

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Limitation 1: each bond represents two electrons, there can only be so many bonds based on the number of valence electrons present.

Limitation 2: each atom has only a certain number of valence orbitals which it can use while making bonds.  Hydrogen only has a 1s orbital available so it's total electron count is limited to 2 ( a single bond).  The second period elements (with only 2s + 2p available) are limited to total electron counts of 8.

Limitation 3: Geometric constraints arise because the atomic orbitals on atoms have certain directional character (with the exception of "s" orbitals which are spherical).  This allows them to bond effectively in only certain ways.  This limitation will be expounded upon later, but suffice it to say that two carbon atoms bonded in the gas phase (C2) cannot exhibit a bond order of 4 because all three 2p orbitals cannot localize electron density between the nuclei simultaneously.

limitation 4 :Exceptions to the "Octet Rule"

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it cannot explain stability of compound

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cannot explain geometry of molecules,cannot explain expanded octet,odd no. of electrons,formation of compounds by inert gases inspite of their octets being complete etc.

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k thnx

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