In Chemistry (Class 11, Chemical Bonding), covalent bonds are formed by the overlapping of atomic orbitals. Depending on how these orbitals overlap, bonds are classified into two types: Sigma (ฯ) bonds and Pi (ฯ) bonds.
Every single covalent bond is always a Sigma bond. A double bond contains 1 Sigma and 1 Pi bond. A triple bond contains 1 Sigma and 2 Pi bonds.
A Sigma bond is formed by the head-on (axial/end-to-end) overlap of atomic orbitals along the internuclear axis.
A Pi bond is formed by the lateral (sideways) overlap of atomic orbitals (usually p-orbitals) perpendicular to the internuclear axis.
| Feature | Sigma (ฯ) Bond | Pi (ฯ) Bond |
|---|---|---|
| Type of Overlap | Head-on / Axial overlap | Sideways / Lateral overlap |
| Strength | Very Strong | Relatively Weak |
| Free Rotation | Atoms can freely rotate around a sigma bond. | Free rotation is restricted (not possible). |
| Independent Existence | Can exist independently (e.g., in single bonds). | Can only exist along with a sigma bond (in double/triple bonds). |
| Electron Cloud | Symmetrical around the internuclear axis. | Divided into two clouds (above and below the axis). |
Because the **Pi bond is weaker** and its electron cloud is more exposed, it is broken much more easily and quickly during a chemical reaction than a Sigma bond.
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