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Difference Between Sigma and Pi Bond

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Last updated date: 01st Mar 2024
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Introduction to Sigma and Pi Bonds

Chemical bonds are forces that keep atoms joined together. Chemical bonds are classified into covalent bonds, coordinate bonds, ionic bonds, and hydrogen bonds. Covalent bonds are those bonds that are formed by sharing of electrons between two atoms. It is also known as a molecular bond. Here in this article, we are going to discuss sigma and pi bonds which are covalent bonds only. And also will discuss what is sigma and pi bond, the difference between the pi bond and sigma bond.


What is Sigma Bond?

The strongest covalent bond which is formed by the head-on overlapping atomic orbitals is called the sigma bond. It is denoted by σ. We find sigma bonds in Alkanes, Alkenes, Alkynes. Formation of sigma bond is given below between the orbitals:


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Properties

  • Sigma molecular orbitals form it up.

  • It is made up of atomic orbitals that overlap head-to-head.

  • Around the bond axis, it is cylindrically symmetrical.

  • Because of the maximal overlap, it is a significantly stronger bond.

  • It is created by the linear overlap of the s-s, s-p, and p-p orbitals.


What is Pi Bond?

The covalent bond which is formed by lateral overlapping of the half-filled atomic orbitals of atoms is called pi bond. It is denoted by π. We find pi bonds in alkenes and alkynes. Formation of pi bond is given below between the two orbitals:


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Properties

  • Pi molecular orbitals make it up.

  • It is generated by the atomic orbitals overlapping side by side.

  • Above and below the two nuclei, there are two sections of the electronic cloud.

  • Because there is less overlap, it is a weaker tie.

  • It's made up of parallel p-p orbital overlap that's coplanar.


Why is Sigma Bond Stronger than the Pi Bond?

The sigma bond is stronger than the Pi bond, according to quantum mechanics, since the orbital paths of Pi bonds are parallel, resulting in less overlap between the p-orbitals. Two atomic orbitals come into contact with each other through two areas of overlap, forming Pi bonds.


Difference Between Pi and Sigma Bonds


S. No

Sigma Bond

Pi Bond

1

Covalent bond which is formed by the head on overlapping atomic orbitals is called sigma bond.

Covalent bond which is formed by lateral overlapping of the half-filled atomic orbitals of atoms is called pi bond.

2

It is the strongest covalent bond.

It is weaker than a sigma bond.

3

It is denoted by σ .

It is denoted by π .

4

In sigma bonds, overlapping orbitals can be pure orbitals, hybrid orbitals and one hybrid and one pure orbital.

In pi bond, overlapping orbitals are always pure orbitals only. Pure orbitals are unhybridized orbitals.

5

It can exist independently. Example -alkane.

It can exist with a sigma bond only. Example- alkene and alkyne.

6

It allows free rotation of orbitals.

It restricts free rotation of orbitals.

7

Atoms with sigma bonds are highly reactive.

Atoms with pi bonds are less reactive than atoms having sigma bonds only.

8

It has cylindrical charge symmetry around the bond axis.

There is no symmetry in pi bonds.

9

It determines the shape of the molecule.

It doesn’t determine the shape of the molecule.

10

Example – CH4



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Example – C2H4



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Key Points

With so many differences, it's clear that these two bonds are crucial. Although the sigma and pi bond differences are complimentary, they are not convertible. Still, there are a few more key points to consider:

  • It is a proven truth that if two atoms form a single bond, the bond will be a sigma bond.

  • It is a truth that if two bonds are present, one must be sigma and the other a pi bond.

  • Also, if there are three bonds, one of them will be a sigma bond, while the other two will be pi bonds.

  • The overlapping of atomic orbitals is the main difference between these bonds. Pi bonds are created by the lateral overlap of two atomic orbitals, whereas sigma bonds are formed by the head-to-head overlapping of atomic orbitals.

  • Sigma bonds are extremely strong covalent bonds, and sigma electrons are the electrons that participate in their creation.

  • S-s overlap, s-p overlap, and p-p overlap are the three most prevalent overlap conditions for forming sigma bonds.

  • The parallel orientation of the two p orbitals in adjacent atoms with proper sideways overlap results in the creation of a pi bond.