Anti-Bonding Molecular Orbitals

Combining atomic orbitals to produce new molecular orbitals is the subject of molecular orbital theory. These new orbitals are formed by the linear combination of atomic orbitals, which results in bonding and antibonding orbitals. The main advantages and disadvantages of electron in antibonding molecular are that it invests significant amounts of time outside the nuclei of the two atoms arranged in antibonding orbitals. 

Positioning electrons in antibonding orbitals diminishes the molecule’s resilience. Electrons would occupy the orbitals following their energy levels. They would first occupy the reduced energy orbitals, followed by the greater energy orbitals. These were the significant advantages of electrons in antibonding molecular orbital. Let’s know more.

Understanding Anti-bonding Molecular Bonding

We can comprehend antibonding molecular orbitals by examining how the atomic orbitals might join in various ways. When atomic orbitals interact in processes that result in mostly destructive interference, antibonding molecular orbitals arise. The main advantages of electrons in antibonding molecular orbitals are that they have larger energy than atomic orbitals. As a result, the molecule (atoms divided by a small distance) has more energy than the divided atoms (atoms divided by a big distance). Moreover, the atoms will choose to be in the reduced energy state of an atom.

An additional attribute of antibonding molecular orbitals is the presence of a “node,” or point of zero density of electron, seen between atoms. The greater MO’s energy will have, the more nodes. On average, antibonding molecular orbitals have additional nodes and energy than bonding molecular orbitals.

What role do antibonding molecular orbitals play?

An antibonding molecular orbital is a sort of molecular orbital in chemical bonding theories that boost the energies of the molecules concerning the separated atoms by weakening the chemical connection between two atoms. An orbital of this kind contains a single or additional node in the bonding area among the nuclei. As a result, the orbital electron density is enhanced outside the bonding area and tries to drive one nucleus far from another, causing reciprocal repulsion among the two atoms.

Why would there be “antibonding” orbitals?

There have always been two methods to add the atomic orbitals when grouping atomic orbitals. They can contribute in such a way that constructive interference occurs. This results in bonding orbitals. Or they can build up to cause destructive interference, resulting in antibonding orbitals. When creating molecular orbitals for compounds with many atoms, there are several atomic orbitals. This indicates that there’s only 1 orbital where all atomic orbitals sum up positively. 

The least energy molecular orbitals, on the other hand, will have much more constructive interference, while the higher energy molecular orbitals, which are antibonding, will have possibilities of destructive interference.

Are electrons present in antibonding molecular orbitals? 

An antibonding molecular orbital has an electron located outside the area among the two nuclei. When two atoms get closer, their electron orbitals start to overlap. The overlap results in forming a molecular relationship between two atoms, each with its unique molecular orbital structure. This is among the essential advantages of excitation of electrons to antibonding molecular orbital.  

These orbitals, like atomic orbitals, obey the Pauli exclusion principle. There can be no two electrons in the same orbital having a similar quantum state. If the source atoms have electrons in places where a relationship would be illegal, the electron will inhabit the higher amount of energy antibonding molecular orbital.

An asterisk sign next to the related kind of molecular orbital denotes antibonding orbitals. σ* orbitals are examples of antibonding sigma orbitals, whereas * orbitals are the examples of pi orbitals of antibonding molecular orbitals. When discussing such orbitals, the sign ‘star’ is frequently placed at the end that denotes sigma-star (* = sigma-star).

Best Example of Antibonding Molecular Orbital

H2- is a diatomic molecule with three electrons. One of them occupies an antibonding orbital. The hydrogen atoms only contain one 1s electron. The 1s orbital may hold two electrons, one with spin “up” and one with spin “down.” The 1s orbital is occupied when a hydrogen atom carries an additional electron, generating an H- ion.

When an H atom and an H- ion come into contact with one other, a sigma link forms among the two atoms. Every atom will give an electron to the bonding, which will complete the lesser energy relationship. To avoid contact with another two electrons, the additional electron will occupy a higher energy phase. The antibonding molecular orbital is the increased energy orbital. The orbital a * is the perfect example of antibonding molecular orbital.

Conclusion

This article discusses the antibonding molecular orbital and the advantages and disadvantages of electrons in antibonding molecular orbital. Since the atomic orbitals are already out of phase, this MO (molecular orbital) has larger energy than the original atomic orbitals. These orbitals are the “reverse” of bonding molecular orbitals. They are created when AO (atomic orbitals) interacts in ways that result in primarily destructive interference. The main characteristic is that these MOs have larger energy than atomic orbitals.