A bond between two atoms that consists of two electrons occupying a bonding molecular orbital with cylindrical symmetry about the internuclear axis. (Note this means that there are no nodes in the wavefunction as you rotate about the internuclear axis.)
A covalent bond in which the electron density is symmetrical about the internuclear axis
a bond formed by the overlap of two hybrid orbitals through areas of maximum electron density
A covalent bond made by the end-on overlapping of two p orbitals. A single covalent bond is a sigma bond.
( bond) Compare with pi bond. In the valence bond theory, a sigma bond is a valence bond that is symmetrical around the imaginary line between the bonded atoms. Most single bonds are sigma bonds.
In chemistry, sigma bonds (σ bonds) are a type of covalent chemical bond. Sigma bonding is most clearly defined for diatomic molecules using the language and tools of symmetry groups. In this formal approach, a σ-bond is symmetrical with respect to rotation about the bond axis.