Formation: Sigma bonds are formed by the head-to-head or axial overlap of atomic orbitals (s-s, s-p, or p-p orbitals).
Location: The electron density is concentrated along the axis connecting the two nuclei of the bonded atoms.
Characteristics:
Example:
In ethane (C₂H₆), the C-C single bond and all C-H bonds are sigma bonds.
Formation: Pi bonds are formed by the side-to-side overlap of p orbitals.
Location: The electron density is concentrated above and below the plane of the nuclei of the bonded atoms.
Characteristics:
Example:
In ethene (C₂H₄), the C=C double bond consists of one sigma bond and one pi bond.
| Feature | Sigma (σ) Bond | Pi (π) Bond |
|---|---|---|
| Formation | Axial overlap of orbitals | Side-to-side overlap of p orbitals |
| Strength | Stronger | Weaker |
| Electron Density | Along the bond axis | Above and below the bond axis |
| Presence | Present in single, double, and triple bonds | Present only in double and triple bonds |
| Rotation | Allows free rotation | Restricts rotation |
Double Bond: One sigma bond + one pi bond.
Triple Bond: One sigma bond + two pi bonds.
Example:
Ethyne (C₂H₂) has a C≡C triple bond, consisting of one sigma bond and two pi bonds.
Understanding these bonds helps explain molecular shapes, bond strengths, and reactivity in chemistry.
