Sigma and Pi Bonds





Sigma and Pi Bonds

According to orbital theory, covalent bond is formed by the result of coupling of electrons with opposite spins belonging to orbitals of outermost orbits of the two atoms. This invariably leads to lowering of potential energy of the system. Such orbitals are said to overlap with each other and the electron pair belongs to both the orbitals.

This overlapping takes place in tow different ways and accordingly different types of bonds are formed:

1. Sigma (\sigma) Bond: A single bond is formed between two atoms by overlapping of orbitals along the same axis is known as sigma bond e.g. formation of bonding shown below:

Sigma and Pi Bonds

Since in such system maximum overlapping is possible hence \sigma bond is strong bond.

2. Pi (\pi) Bond: The bond formed between two atoms by the sidewise overlapping of the two orbitals is called pi bond e.g.

Since in such system there is a partial overlapping hence the bond is weak and reactive

Sigma and Pi Bonds

Comparison between \sigma \text{and} \pi-Bonds

Sigma-bond

Pi-bond
1.Stronger overlapping makes it stronger (stable) bond.

2.Relativity of compound

\propto \dfrac{1}{\text{No. of} \sigma \text{bond}}

3.  \text{Stability of compound} \propto \\ \text{No. of} \sigma \text{bond}

Min. and Max. No of \sigma bonds between two bonded atoms is one

4.Decides shape of molecule

Weak overlapping makes it less stable bond

 

\text{Relativity} \propto \text{No. of} \pi-\text{bonds}

 

\text{Stability} \propto \dfrac{1}{\text{No. of} \pi \text{bonds}}

Min. of zero

Max. is two.

Shorter bond lengths of molecule

 

To find no of \sigma, \pi bonds:

( - ) \Rightarrow 1 \sigma \\ ( = ) \Rightarrow (1 \sigma, 1 \pi) \\ (\equiv ) \Rightarrow 1 \sigma, 2 \pi

Sigma and Pi Bonds



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