Sigma bond

strongest type of covalent chemical bond; formed by head-on overlapping between atomic orbitals.

A sigma bond (σ bond) is a type of chemical bond. It is the strongest one of the covalent type.[1] In a sigma bond, the atomic orbitals from two atoms which are nearby go one on top of each other. This is different from a pi bond where they touch sideways. This is why a sigma bond is stronger. Sigma bonds can involve s, p, d or f orbitals. They must however be of the right symmetry to be able to form the bond.

A sigma bond between two atoms

Since the σ bond is strong, the bonding orbital is low in energy. This also means that the antibonding orbital σ* is high in energy.


  1. Moore, John; Stanitski, Conrad L.; Jurs, Peter C. (2009). Principles of Chemistry: The Molecular Science. Cengage Learning. ISBN 978-0-495-39079-4.