difference between sigma and pi bonds

Sigma (σ) and pi (π) bonds are two types of covalent bonds that form between atoms when they share electrons. They differ in their molecular orbital overlap and bonding characteristics:

Sigma (σ) Bonds

1. Head-On Overlap: Sigma bonds result from the head-on overlap of atomic orbitals (usually s or p orbitals) along the bond axis. The electron density is concentrated along the internuclear axis, creating a strong bond.
2. Stronger and More Stable: Sigma bonds are generally stronger and more stable than pi bonds because of the direct and effective overlap of orbitals.
3. Single Bonds: In most cases, single covalent bonds are sigma bonds. For example, in a molecule like H2, the bond formed between two hydrogen atoms is a sigma bond.
4. Rotational Freedom: Sigma bonds allow free rotation around the bond axis because the electron density is symmetrical along the axis. This rotation is not restricted as long as the sigma bond itself is not broken.

Pi (π) Bonds

1. Side-to-Side Overlap: Pi bonds result from the side-to-side overlap of atomic orbitals (usually p orbitals) that are parallel to each other. The electron density is concentrated above and below the internuclear axis.
2. Weaker and Less Stable: Pi bonds are generally weaker and less stable than sigma bonds due to the less effective overlap of orbitals.
3. Double and Triple Bonds: In molecules with double or triple bonds, one or more of the bonds typically involve pi bonds. For example, in H2C=CH2 (ethylene), the bond between the two carbon atoms is a sigma bond, while the two bonds between the carbon and hydrogen atoms are pi bonds.
4. Restricted Rotation: Pi bonds restrict the rotation of atoms around the bond axis because breaking the pi bond requires the electrons to be reconfigured. As a result, double and triple bonds with pi bonds exhibit geometric (cis-trans) isomerism.