What Is Molecular Orbital Theory?

A molecular orbital is the most productive and general model of chemical bonding made by exchanging more than one electron. The molecular orbital theory consists of various quantitative calculations and complex mathematical illustrations. Regarding quantum mechanics, the theory of molecular orbital is quite similar to the exchange of electrons with its distribution in the atomic orbital theory. In any molecule, the electron around an atom contains discrete energies, and there are many more similarities in atomic and molecular orbitals. The molecular orbital is packed with the presence of two electrons and an opposite spin in its orbit.

Molecular Orbital Theory:

A chemical bonding between the atoms takes place only when the total attractive forces among the single electron and double nuclei receive extended electrostatic repulsion among both nuclei. For such chemical bonding, the electron must lie under the binding region, and if it is present in the anti-binding region, it adds the repulsion force to push between the two nuclei.

The molecular orbital theory explains that mentions the paramagnetism force in any molecule. According to this theory, the atomic orbitals combine and form molecular orbitals. The theory also determines the quantity of chemical bonding with specific molecules; complex bonding of molecules is difficult to determine with Lewis’s structure and any violations of the octet rule for chemical bonding.  

According to molecular orbital theory, it is easily visualized by the two distinct isolated atoms and atomic orbitals behaving separately. As a result, the intermolecular distance between two atoms corresponding to the molecules is gradually closer; such formed structure is known as molecular orbitals.

Example: To understand it briefly, let us consider the simplest example of a molecule orbital, H2+. It is a hydrogen molecule ion consisting of nuclei that charge +1 and share only one electron among them. Here is the chemical structure:

(+) 2 protons + (+) 1 electrons = (+ +) dihydrogen ion

Here the two H nuclei are in motion toward each other in a specific atomic orbital; the isolated atoms here gradually form a molecular orbital. As per the molecular orbital theory, the electron with the greatest charge lies under two nuclei.

Getting a brief idea about what is molecular orbital theory, in this example, the electrons are ready to exert force on both the nuclei simultaneously to arrange the molecular orbital in a specific manner.

Molecular orbital representation:

The molecular orbital theory scheme is represented by bonding and antibonding molecular orbitals. The atomic valence electrons are filled with low energy molecules before the higher energy molecules. In the dihydrogen ions, all the included molecules move to the bonding orbital, and thus the antibonding orbital is left empty.

According to molecular orbital theory, a single orbital can attain only two electrons. But in the case of H2+ the orbital is half-filled. As the structure of the H2+ is stable in terms of energy, a single electron in the dihydrogen ion is potent enough to deplete the energy of two nuclei of hydrogen.

Dihydrogen ion: bond order=0.5, bond energy = 270 KJ

Adding one electron, H2+ = -270 KJ

Adding second electron, H2 = – 452 KJ (total -540 KJ)

Here the single electron lowers the potency of two nuclei by -270 KJ and two electrons collectively reduce it to – 540 KJ.

Hence to consider what is molecular orbital theory, here in dihydrogen ion, the two electrons in the molecular orbit lower the energy and break the hydrogen ions by 452 KJ collectively. However, the potential energy here is not completely depleted as electrons present in the same molecular orbital receive a repulsion force against stabilized forces.

Diatomic Molecules Representing Molecular Orbitals:

In the molecular orbital theory, specific diatomic molecules are involved with two 1s atomic orbitals. The valence shell orbitals are considerably important in such molecular orbitals, and atomic orbitals present in the diatomic molecules are of higher order. In these molecules, the 1s atomic orbitals comprise the nucleus’s electric charge present according to the atomic character and bond formation. Below is the listing and description of diatomic molecules:

Dilithium:

• Representation formula = Li2 
• Bond order = 1
• Bond energy = 110 Kj

Lithium Hydride:

• Representation formula = LiH
• Type of bond = covalent bond
• Bond order = 1
• Bond energy = 243 Kj

Conclusion:

The molecular orbital theory represents the nature and behaviour of the chemical bonds as per the behaviour of electrons. All the bonds in the molecular orbitals are generally covalent. The bonds formed in the molecular orbitals paramagnetism between the nuclei result in lower energy. Most of its processes are according to the atomic orbitals, and the calculation of molecular orbital comprises several quantitative complex calculations. Molecules like dihydrogen from their chemical bonds in the molecular orbitals with the exchange of a single electron within its orbit.