The major difference between sigma bond and pi bond is that Sigma bonds (σ) are single covalent bonds formed by the direct overlap of atomic orbitals along the bond axis, allowing free rotation while Pi bonds (π) are double or triple covalent bonds formed by the side-to-side overlap of p orbitals, restricting rotation and creating a weaker bond.
What Is Sigma Bond?
A sigma (σ) bond is a type of covalent chemical bond formed between two atoms when their atomic orbitals overlap head-on along the bond axis. Sigma bonds are typically found in single bonds (sigma single bonds) and represent the strongest and most stable type of covalent bond.
They allow for free rotation around the bond axis, making them flexible and less restricted in terms of molecular structure.
Example of Sigma Bond
In a Lewis structure or molecular orbital diagram, the sigma bond in H2 is typically depicted as H-H or σ(H-H).
What Is Pi Bond?
A pi bond (π bond) is a type of covalent bond formed when two atomic orbitals overlap side by side in a double or triple bond. Unlike sigma bonds, which have direct head-on overlap, pi bonds involve the parallel overlap of two p orbitals (or d orbitals in triple bonds) above and below the bond axis.
Pi bonds are weaker than sigma bonds and restrict the rotation of atoms around the bond axis, contributing to the rigidity of double and triple bonds in molecules.
Example of Pi Bond
An example of a pi (π) bond can be found in the ethene (ethylene) molecule, which is composed of two carbon atoms double-bonded to each other and each bonded to two hydrogen atoms. The pi bond exists in the double bond between the two carbon atoms.
Sigma Bond Vs Pi Bond
The primary difference between the sigma bond and the pi bond is given below:
| Characteristic | Sigma (σ) Bond | Pi (π) Bond |
| Type of Overlap | Head-on overlap | Side-to-side overlap |
| Bond Location | Along the bond axis (internuclear axis) | Above and below the bond axis |
| Number of Bonds | Every single bond has one sigma bond | Typically found in double and triple |
| Strength | Generally stronger | Generally weaker |
| Bonding Electrons | Occupy a cylindrical space between atoms along the bond axis | Occupy two parallel regions above and below the bond axis |
| Mobility | Sigma bonds allow the rotation of atoms | Sigma bonds allow the rotation of atoms |