Why sigma bonds are stronger than pi bond
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pi bonds are usually weaker than sigma bond . quantum mechanics says this is becoz the orbital path are parallel. so , there is much less over between the p orbitals.
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The reason behind this is the orientation of the overlapped orbitals. Sigma bonds result from head-on(co-axial) overlapping while pi bonds are outcome of lateral(para-axial) overlapping. Here is a pictorial representation of ethene(sp2 hybridized C atoms) :
enter image description here
The greater the extent of overlapping, the higher the probability of finding the valence electrons in between the nuclei and hence the bond will be stronger & shorter.
In MOT, this can be explained using Overlap Integral. This is how Atkins depicts it :
enter image description here
In simple terms, after forming a sigma-bond (a pre-requisite for pi-bonds), the two atoms get locked along the inter-nuclear axis. As a result, the orbitals available for pi-bonding can only partially overlap, thus forming a weaker bond.
enter image description here
The greater the extent of overlapping, the higher the probability of finding the valence electrons in between the nuclei and hence the bond will be stronger & shorter.
In MOT, this can be explained using Overlap Integral. This is how Atkins depicts it :
enter image description here
In simple terms, after forming a sigma-bond (a pre-requisite for pi-bonds), the two atoms get locked along the inter-nuclear axis. As a result, the orbitals available for pi-bonding can only partially overlap, thus forming a weaker bond.
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