Molecular orbital theory.
Molecular orbital theory


In this article, we will discuss about the molecular orbital theory (MOT). This theory is a powerful tool use to understand and predict the properties of molecules. It also help in analyzing the behavior of electrons within them. This theory provides a deeper insight into the nature of chemical bonds, allowing scientists to explain and predict various molecular properties. We will explore the basics of molecular orbital theory, examine the structures of molecules, and provide references.


Molecular Orbital Theory (MOT) is a fundamental concept in chemistry that provides a deeper understanding of chemical bonding and the behavior of molecules. Developed in the early 20th century, MOT revolutionized our comprehension of molecular structure and properties. This article aims to explore the key principles of molecular orbital theory, its applications, and its significance in modern chemistry.


Molecular Orbital Theory is based on the concept that atomic orbitals combine to form molecular orbitals, which are regions of space where electrons are most likely to be found. These molecular orbitals can be bonding or antibonding, depending on the constructive or destructive interference of atomic orbitals.


In MOT, the combination of atomic orbitals leads to the formation of bonding and antibonding molecular orbitals. Bonding orbitals result from constructive interference, where the electron density between the nuclei increases, stabilizing the molecule. Conversely, antibonding orbitals arise from destructive interference, leading to a node between the nuclei and destabilizing the molecule. Bonding orbitals are of low energy and highly stable, while anti-bonding are of high energy and less stable.


Molecular orbitals can be classified into sigma (σ) and pi (π) bonds. Sigma bonds are formed by the head-on overlap of atomic orbitals, allowing for free rotation around the bond axis. Pi bonds, on the other hand, result from the sideways overlap of atomic orbitals, restricting rotation due to the presence of nodal planes.


Molecular Orbital Theory has numerous applications in understanding chemical phenomena. It provides insights into the stability and reactivity of molecules, explaining properties such as bond length, bond energy, and molecular shape. MOT also helps elucidate the behavior of complex molecules, such as aromatic compounds and transition metal complexes.


Molecular orbital diagrams are graphical representations that illustrate the distribution of electrons in molecular orbitals. In these diagrams, molecular orbitals are represented by horizontal lines, and electrons are depicted as arrows. The lower energy molecular orbitals are filled first, following the Pauli exclusion principle and Hund’s rule.


Let’s consider the example of the diatomic molecule, hydrogen (H2). The molecular orbital diagram for H2 shows that the two 1s atomic orbitals combine to form two molecular orbitals: a bonding σ1s orbital and an antibonding σ*1s orbital. The two electrons in the H2 molecule occupy the bonding σ1s orbital, resulting in a stable molecule.

Molecular orbital diagram of H2.
Molecular orbital diagram of H2

2. OXYGEN (O2):

Another example is the diatomic molecule, oxygen (O2). The molecular orbital diagram for O2 shows that the combination of two 2p atomic orbitals from each oxygen atom results in the formation of two molecular orbitals: a bonding σ2p orbital and an antibonding σ*2p orbital. The electrons in the O2 molecule occupy the bonding σ2p orbitals, leading to a stable molecule.

Molecular orbital diagram of oxygen.
Molecular orbital diagram of oxygen


Molecular Orbital Theory has played a crucial role in advancing our understanding of chemical bonding and reactivity. It has paved the way for the development of new materials, drugs, and catalysts. Additionally, MOT has been instrumental in explaining the electronic structure of organic compounds, facilitating the design of novel drugs and materials with tailored properties.


Molecular Orbital Theory is a powerful tool that allows chemists to unravel the intricacies of chemical bonding and molecular behavior. By providing a detailed understanding of molecular structure and properties, MOT has revolutionized the field of chemistry. Its applications in various areas, from drug design to materials science, highlight its significance in modern research. As our knowledge of molecular orbital theory continues to expand, so too does our ability to manipulate and engineer molecules for a wide range of applications.


Atkins, P., & Friedman, R. (2005). Molecular Quantum Mechanics. Oxford University Press.

Szabo, A., & Ostlund, N. S. (1996). Modern Quantum Chemistry: Introduction to Advanced Electronic Structure Theory. Dover Publications.

Huheey, J. E., Keiter, E. A., & Keiter, R. L. (1997). Inorganic Chemistry: Principles of Structure and Reactivity. HarperCollins College Publishers.

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