What NEET Asks
- Identify the number of sigma and pi bonds in various organic and inorganic molecules.
- Compare the properties (strength, rotation) of sigma and pi bonds.
- Questions often integrate hybridization concepts with bond types.
Key Points
- Sigma (σ) bond: Formed by the axial (head-on) overlap of atomic orbitals (s-s, s-p, p-p). Electron density is maximum along the internuclear axis.
- Pi (π) bond: Formed by the sideways (lateral) overlap of unhybridized p-orbitals. Electron density is above and below the internuclear axis.
- A single bond always contains one sigma bond.
- A double bond consists of one sigma and one pi bond.
- A triple bond consists of one sigma and two pi bonds.
- Sigma bonds are stronger than pi bonds due to greater extent of overlap.
- Sigma bonds allow free rotation around the bond axis; pi bonds restrict rotation.
Must-Know Formula / Reaction
- Bond Counting Rules:
- Single covalent bond = 1σ bond
- Double covalent bond = 1σ bond + 1π bond
- Triple covalent bond = 1σ bond + 2π bonds
- Explanation: These rules allow systematic calculation of bond types in any molecule.
Common Mistakes
- Students often confuse the relative strengths; remember sigma is stronger due to head-on overlap.
- Don't forget to count C-H bonds as sigma bonds in organic compounds.
- Incorrectly assuming all bonds in a multiple bond contribute equally to strength or rotation. Pi bonds are weaker and prevent free rotation.
Rapid Revision
Sigma bonds are formed by head-on overlap, are strong, and allow free rotation. Pi bonds are formed by sideways overlap, are weaker, and restrict rotation. Single bonds are 1σ; double bonds are 1σ, 1π; triple bonds are 1σ, 2π. Count carefully, especially in complex structures.