Antibonding orbitals are molecular orbitals that are formed when atomic orbitals combine in such a way that the resulting electron density is located outside the region between the two nuclei. Electrons in these orbitals weaken the bond between atoms and raise the overall energy of the molecule.
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Antibonding orbitals are denoted with an asterisk (*), such as $\sigma^*$ or $\pi^*$.
Electrons in antibonding orbitals contribute to destabilizing the molecule.
The energy of antibonding orbitals is higher than that of bonding orbitals formed from the same atomic orbitals.
In Molecular Orbital Theory, if more electrons occupy antibonding than bonding orbitals, the molecule is unstable.
The formation of antibonding orbitals occurs during both sigma ($\sigma$) and pi ($\pi$) bond formations.
Review Questions
What is an antibonding orbital and how does it affect molecular stability?
How are antibonding orbitals represented in molecular orbital diagrams?
Why do electrons in antibonding orbitals increase the energy of a molecule?
Related terms
Bonding Orbitals: Molecular orbitals formed by constructive interference of atomic wave functions, resulting in increased electron density between nuclei and stabilizing the molecule.
$\sigma$ Bond: A type of covalent bond formed by head-on overlap of atomic orbitals, creating a bonding molecular orbital along the axis connecting two nuclei.
$\pi$ Bond: A type of covalent bond formed by sideways overlap of p-orbitals, creating bonding molecular orbitals above and below the plane of nuclei.