Antibonding molecular orbital

Definition

An antibonding molecular orbital is a type of molecular orbital that is formed when atomic orbitals combine in such a way that there is a region of higher energy between the nuclei of the bonded atoms, effectively destabilizing the molecule. These orbitals typically have a nodal plane between the two nuclei and result in an overall reduction in bond strength when occupied by electrons, often leading to weaker interactions between the atoms involved.

5 Must Know Facts For Your Next Test

1. Antibonding molecular orbitals are designated with an asterisk (*) symbol, such as $$ ext{σ}^*$$ or $$ ext{π}^*$$, to indicate their nature as antibonding.
2. Electrons in antibonding molecular orbitals contribute to the weakening of the bond between atoms, making them less stable than those in bonding orbitals.
3. The presence of electrons in antibonding molecular orbitals can even lead to bond dissociation if they outnumber those in bonding orbitals.
4. In diatomic molecules, the filling order of molecular orbitals follows the Aufbau principle, where bonding orbitals are filled before antibonding ones.
5. Antibonding molecular orbitals arise from the combination of atomic orbitals with opposite phases, leading to destructive interference and an increase in energy.

Review Questions

• How do antibonding molecular orbitals differ from bonding molecular orbitals in terms of stability and energy?
  • Antibonding molecular orbitals are characterized by having higher energy levels compared to bonding molecular orbitals. While bonding orbitals promote stability by lowering energy through constructive interference, antibonding orbitals destabilize the molecule by creating a region of higher energy between the nuclei. When occupied by electrons, antibonding orbitals weaken the bond between atoms and can lead to increased instability within the molecule.
• Discuss how the occupation of antibonding molecular orbitals influences the overall properties of a molecule.
  • The occupation of antibonding molecular orbitals significantly affects a molecule's stability and reactivity. When these orbitals are filled with electrons, they counteract the stabilizing effects of bonding molecular orbitals, resulting in weakened bonds and higher reactivity. This can lead to lower bond dissociation energies and make the molecule more susceptible to chemical reactions or breaking apart under certain conditions.
• Evaluate the implications of antibonding molecular orbitals on predicting molecular behavior in different environments.
  • Understanding antibonding molecular orbitals is crucial for predicting how molecules will behave under various conditions. For example, if a molecule has several electrons occupying antibonding orbitals, it may be more reactive and less stable, influencing its interactions with other molecules. In environments such as high temperatures or pressures, these effects can be amplified, leading to different chemical pathways or states of matter. Therefore, evaluating the filling of antibonding versus bonding orbitals helps chemists anticipate changes in molecular behavior and design reactions accordingly.

Related terms

bonding molecular orbital: A bonding molecular orbital is formed when atomic orbitals combine constructively, resulting in a region of lower energy between the nuclei and promoting stability in the molecule.

molecular orbital theory: Molecular orbital theory is a method for describing the electronic structure of molecules where atomic orbitals are combined to form molecular orbitals that can be occupied by electrons.

nodal plane: A nodal plane is a region in a molecular orbital where the probability of finding an electron is zero, indicating areas of destructive interference between wave functions.