Britannica Sources used in this answer

How does a sigma bond differ from a pi bond?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Diagram showing the formation of a polar covalent bond in a water molecule, with two hydrogen atoms bonding to one oxygen atom to form H2O, illustrating shared electrons and chemical reaction. — covalent bond In polar covalent bonds, such as that between hydrogen and oxygen atoms, the electrons are not transferred from one atom to the other as they are in an ionic bond. Instead, some outer electrons merely spend more time in the vicinity of the other atom. The effect of this orbital distortion is to induce regional net charges that hold the atoms together, such as in water molecules.

In chemistry, the primary difference between a sigma bond and a pi bond lies in the spatial distribution of the shared electron pair and the nature of the orbital overlap.123

Sigma ( $σ$ ) Bond: These bonds are characterized by cylindrical symmetry about the internuclear axis—the line connecting the two bonded nuclei. The electron pair occupies an orbital located primarily between the two atoms. This head-to-head overlap creates a strong, stable connection. A single bond in a Lewis structure is always a sigma bond.31
Pi ( $π$ ) Bond: These bonds form when orbitals overlap side-to-side rather than head-to-head. The resulting electron density is located in two regions roughly parallel to the internuclear axis, rather than directly on it. Because the maximum electron density is off the axis, pi bonds are generally not as strong as sigma bonds.32

A pi bond cannot exist independently; it only forms in conjunction with a sigma bond. For instance, a double bond consists of one sigma and one pi bond, while a triple bond comprises one sigma and two pi bonds.234