A
three-center two-electron bond is an
electron-deficient chemical bond where three
atoms share two
electrons. The combination of three
atomic orbitals form three
molecular orbitals: one bonding, one
non-bonding, and one
anti-bonding. The two electrons go into the bonding orbital, resulting in a net bonding effect and constituting a chemical bond among all three atoms. In many common bonds of this type, the bonding orbital is shifted towards two of the three atoms instead of being spread equally among all three. The simplest example of a 3c-2e bond is in the
trihydrogen cation, .