Sigma bond | Pi bond | |
|---|---|---|
Formation | The sigma bond is formed by the head-to-head (or end-to-end) overlap of the hybrid or atomic orbitals. | A pi bond is an additional bond over the sigma bond formed by the side-to-side (or lateral) overlap of the perpendicular p-atomic orbitals. |
Image |  |  |
Representation | A sigma bond is denoted by the symbol σ and as a dash (-) in a molecular structure. | A pi bond is represented using a symbol π and drawn as an additional dash bond over the existing sigma bond as = (for one pi and one sigma) or ≡ (for two pi and one sigma bond). |
Pictorial Representation | For example, all the seven bonds in H3C-CH3 are sigma (σ) bonds.
| For example, the molecule H2C=CH2 has five sigma and one pi bond. At the same time, H-C≡C-H has three sigma (σ) and two pi (π) bonds.
|
Bond Rotation | Since the sigma bond is formed along the internuclear axis, the bond can undergo symmetric rotation. | The pi bond rotation is restricted due to the lateral orbital overlap. |
Strength | Sigma bonds are formed by head-to-head overlap along the internuclear axis, so the overlapping area is larger. The bond formed is, therefore, stronger. | The pi bond is weaker than the sigma bond since the p-orbital electron densities are diffused and placed on either side of the internuclear axis resulting in a less efficient overlap. So, it’s easier to break a pi bond than a sigma bond. |
