What is the Difference Between Bonding and Antibonding Electrons

The main difference between bonding and antibonding electrons is that bonding electrons occupy molecular orbitals that result from the constructive interference of atomic orbitals, whereas antibonding electrons occupy molecular orbitals formed when atomic orbitals overlap out of phase.

In the molecular orbital theory, atomic orbitals from different atoms overlap, giving rise to molecular orbitals. The two main categories of molecular orbitals are bonding and antibonding orbitals, and the behavior of electrons in these orbitals shapes the very essence of chemical bonding.

Key Areas Covered

1. What are Bonding Electrons
      – Definition, Features 
2. What are Antibonding Electrons
      – Definition, Features 
3. Similarities Between Bonding and Antibonding Electrons
      – Outline of Common Features
4. Difference Between Bonding and Antibonding Electrons
      – Comparison of Key Differences
5. FAQ: Bonding and Antibonding Electrons
      – Frequently Asked Questions

Key Terms

Bonding Electrons, Antibonding Electrons

What are Bonding Electrons

Bonding orbitals are molecular orbitals formed by the constructive overlap of atomic orbitals, leading to a lower energy state and stability. Electrons in bonding orbitals contribute to the formation and stability of a chemical bond. Consider a classic example: the formation of a diatomic molecule, such as hydrogen (H₂). Each hydrogen atom brings its 1s atomic orbital to the molecular playground. As the atoms approach each other, their 1s orbitals overlap in-phase, giving rise to a bonding molecular orbital.

ψ_bonding​ = ψ_1sA​​ + ψ_1sB​​

Here, ψ_1sA​​ and ψ_1sB​​ represent the wave functions of the 1s orbitals of the two hydrogen atoms. The constructive interference of these wave functions results in a bonding orbital, a region of space where bonding electrons reside.

Bonding orbitals have lower energy than the individual atomic orbitals from which they originate. This lower energy state reflects the stability conferred upon the molecule by the presence of bonding electrons. Within bonding orbitals, a region of high electron density is situated between the two nuclei. This concentrated electron density acts as a gravitational force, pulling the positively charged nuclei toward each other.

The stability of a molecule is intricately linked to its number of bonding electrons. According to the fundamental tenets of molecular orbital theory, the more bonding electrons a molecule has, the more stable it becomes. This stability arises from the lowering of the overall energy state of the molecule due to the formation of bonding orbitals.

What are Antibonding Electrons

Antibonding orbitals are molecular orbitals formed by the destructive overlap of atomic orbitals, leading to higher energy and reduced stability. Electrons in antibonding orbitals counteract the stabilizing effects of bonding electrons and can weaken or oppose the formation of a chemical bond. For example, consider the encounter of two hydrogen atoms to form a diatomic molecule (H₂). Each hydrogen atom contributes its 1s atomic orbital to the molecular union. However, if these orbitals overlap out of phase, destructive interference occurs, forming an antibonding molecular orbital.

ψ_antibonding​ = ψ_1sA ​​− ψ_1sB​​

In this expression, ψ_1sA​​ and ψ_1sB​​ represent the wave functions of the 1s orbitals of the two hydrogen atoms. The subtraction of these wave functions results in the destructive interference characteristic of antibonding orbitals.

Antibonding orbitals have higher energy compared to the original atomic orbitals. This higher energy state signifies a less stable configuration for the molecule. Antibonding orbitals are regions of low electron density between the two nuclei. Unlike bonding orbitals, which contribute to the attractive forces holding nuclei together, antibonding orbitals weaken these forces.

Antibonding electrons introduce an element of instability to a molecule. Unlike their bonding counterparts, which contribute to the cohesive forces holding atoms together, antibonding electrons disrupt this harmony. The very nature of their orbital arrangement weakens the attractive forces between atomic nuclei, rendering the molecule more susceptible to disruption.

Similarities Between Bonding and Antibonding Electrons

• The principles of quantum mechanics govern both bonding and antibonding electrons.
• Both types of electrons originate from the overlap of atomic orbitals from different atoms.

Difference Between Bonding and Antibonding Electrons

Definition

Bonding orbitals are molecular orbitals formed by the constructive overlap of atomic orbitals, leading to a lower energy state and stability. On the other hand, antibonding orbitals are molecular orbitals formed by the destructive overlap of atomic orbitals, leading to higher energy and reduced stability.

Formation

Bonding electrons form due to the constructive interference of atomic orbitals, while antibonding electrons form due to the destructive interference of atomic orbitals.

Overlap

In bonding electrons, overlapping atomic orbitals combine in-phase, leading to constructive interference and forming a bonding orbital. Meanwhile, in antibonding electrons, overlapping atomic orbitals combine out of phase, resulting in destructive interference and the formation of an antibonding orbital.

Energy

Bonding electrons reside in molecular orbitals with lower energy than the original atomic orbitals, whereas antibonding electrons reside in molecular orbitals with higher energy than the original atomic orbitals.

FAQ: Bonding and Antibonding Electrons

What is meant by BMO?

BMO refers to bonding molecular orbitals. Bonding molecular orbitals result from the constructive overlap of atomic orbitals, contributing to the formation of chemical bonds.

What is meant by ABMO?

ABMO refers to antibonding molecular orbitals. Antibonding molecular orbitals result from the destructive overlap of atomic orbitals and have higher energy than those from which they originate.

Why is BMO more stable than ABMO?

BMOs exhibit greater stability than ABMOs due to their lower energy levels in contrast to the higher energy levels associated with antibonding molecular orbitals.

Conclusion

Bonding electrons occupy molecular orbitals that result from the constructive interference of atomic orbitals, whereas antibonding electrons occupy molecular orbitals formed when atomic orbitals overlap out of phase. Thus, this is the main difference between bonding and antibonding electrons.

Reference:

1. “Antibonding Molecular Orbital.” Wikipedia. Wikipedia Foundation.
2. “Bonding Electron.” Wikipedia. Wikipedia Foundation.

Image Courtesy:

1. “H2wikibondingmo” By Chemiscool – Own work (CC BY-SA 4.0) via Commons Wikimedia 
2. “Dihydrogen-LUMO-phase-3D-balls” By Benjah-bmm27 – Own work (Public Domain) via Commons Wikimedia