A three-electron bond occurs when two nuclei share two delocalised electrons in a sigma molecular orbital, and a single delocalised electron in a sigma* orbital. Sigma* is an antibonding orbital, meaning that it has more energy than an s atomic orbital. Since electrons tend to lower-energy orbitals when possible, three-electron bonds are weaker than normal sigma bonds (about half the dissociation energy).

Three-electon bonds, as noted above, have approximately the same dissocation energy as single-electron bonds. Let S be the energy of an electron in an S atomic orbital, S-d the energy of an electron in a sigma molecular orbital. Then an electron in a sigma* orbital has energy S+d, so we have that the total energy is (S-d) + (S-d) + (S+d) = 3S-d: d less than if there were no bond. In a single-electron bond, the electron has energy S-d, also d less than if there were no bond. Hence the two have the same strength, approximately half of the 2d dissociation energy of a normal sigma bond.