Difference between Sigma and Pi Bond and its Importance

Studying chemical bonds is important as well as interesting in the area of chemistry. Actually a bond is a force that keeps the atoms together during their interaction. Also, chemical bonds are classified into various types such as an ionic bond, covalent bond, polar bond, and hydrogen bond. There are many other different kinds of bonds in such mentioned categories. Here we will discuss the details of sigma bonds and pi bonds, which are considered as the covalent bonds. It is a fact that covalent bonds are playing very important for the chemicals and their existence. Also, the article will help to get a concrete difference between sigma and pi bond.

What is Sigma Bond?

The bond formed by the face to face overlapping between two atomic orbital’s ( between s – s orbital’s, p – p orbital’s or s – p orbital’s ), is called a sigma bond. Sigma bond is formed by the overlapping between two atomic orbitals in face to face. This may be between two ‘s’ orbitals, two ‘p’ orbitals, or even in between one ‘s’ orbital and one ‘p’ orbital.

These bonds are more stable with their lower energy. They show no bond resonance or hyper-conjugation. In these bonds, electron pairs exist between two atoms with the localized bonding. Therefore sigma bond is stronger than other bonds. Compounds with localized sigma bonding can be completely elaborated by a single Lewis structure. Also, their many properties like bond lengths, bond energies, and dipole moments can be predicted easily.

What is a pi bond?

This bond is formed by sidewise or parallel overlapping between two orbitals such as py-py orbitals or Pz-Pz orbitals. Its stability is less due to higher energy. Pi bond participates in the resonance without showing hyper-conjugation. In these bonds, one or more electron pairs can move from one other atom and hence making the delocalized chemical bonding. Pi bonds are loosely bounded and hence these are weak bonds. Pi bond shows the properties of conjugated systems because all such systems have the alternate single and double or triple bonds.

Difference between Sigma and Pi Bond

difference between sigma and pi bond

The important difference between the sigma and pi bond

Sr No.	Parameters	Sigma Bond	Pi Bond
1.	Bond Formation	During its formation, overlapping orbitals can be one hybrid orbital and a single pure orbital. Also, it can be two pure orbitals and two hybrid orbitals.	In its bond formation, overlapping orbitals should be two un-hybridized orbitals.
2.	Rotation	Sigma bonds exist independently and they allow the free rotation.	These bonds exist along with the sigma bond with the restricted rotation.
3.	Order of formation	These bonds are formed at first when atoms interact.	These bonds are formed between two atoms after the formation of sigma bonds already.
4.	Symmetricity	These are having the cylindrical charge symmetry around the bond axis.	In pi bonds, there is no symmetry exist.
5.	Reactive nature	Atoms having sigma bonds are highly reactive.	Atoms having pi bonds are not as reactive in nature as sigma bonds.
6.	Molecular shape	Sigma bond helps to determine the shapes of molecules.	Pi bonds are not useful for the determination of shapes of molecules.

Some important points:

It is obvious that these two bonds are very important with the many differences. Although the difference between sigma and pi bond are complementary with each other. Still, some more important points are significant as follows:

It is a fact that, if there is a single bond between two atoms, then this bond will be sigma bond.
It is a fact that, if there are two bonds, then one must be sigma with the other one as a pi bond.
Also, it is a fact that, if there are three bonds, then one bond will be a sigma bond with the two pi bonds.
These bonds mainly differ in the overlapping of atomic orbitals. Sigma bonds are due to the head-to-head overlapping of atomic orbitals on the other hand pi bonds are formed by the lateral overlap of two atomic orbitals.
Sigma bonds are very strong covalent bonds and the electrons participating in its formation are known as sigma electrons.
The three most common conditions for the overlap for giving sigma bonds are s-s overlap, s-p overlap, and p-p overlap.
Pi bond formation happens by the parallel orientation of the two p orbitals in adjacent atoms with proper sideways overlap.