Sigma Bond
A covalent bond formed by the head-on overlap of atomic orbitals, with electron density concentrated along the internuclear axis.
Unit
kJ/mol
In depth
Sigma overlap is the most effective kind, making these the strongest covalent bonds. Because the electron distribution is cylindrically symmetric about the axis, free rotation is possible around a single bond. Every covalent linkage contains exactly one sigma bond, whatever its order.
Examples in the real world
The s–s bond in H₂, the sp³–s bonds in methane, and the single C–C bond in ethane, about which the groups rotate freely.