What is the Molecular Orbital theory?

What is the Molecular Orbital theory?

The Molecular Orbital Theory most commonly known as MOT is a theory that is based on thechemical bonding developed at the beginning of the twentieth century. The famous scientist F. Hund and R. S. Mullikanhave described the structure and properties of different molecules. The valence-bond theory however has failed to adequately explain as to how certain molecules contains two or more equivalent bonds. This also explains the bond orders that lie between that of a single bond and that of a double bond, in such a way that the bonds in resonance-stabilized the molecules. This is where the molecular orbital theory haveemerged out to be more powerful than the valence-bond theory as the orbitals described by the MOT will reflect the geometries of the molecules to which it is being applied.

Here the key features of the molecular orbital theory are elaborated below:

  • The theory states that the total number of molecular orbitals that is formed will always is equal to the total number of atomic orbitals that are offered by the bonding species.
  • There are different types of molecular orbitals like bonding molecular orbitals, anti-bonding molecular orbitals, and non-bonding molecular orbitals. Out of these, the anti-bonding molecular orbitals will always have higher energy and on the other hand the bonding molecular orbitals will always have lower energy as compared to the parent orbitals.
  • The electrons arealways filled into molecular orbitals in the increasing order of orbital energy. This means the orbital that have the lowest energy to the orbital will be first followed by with the highest energy.
  • The most effective combinations of atomic orbitals will happen when there is a combination of atomic orbitalsthat have similar energies.

In simple words, the molecular orbital theory states that each atom will combine together and form molecular orbitals. Due to the presence of such arrangement,the electrons are found in various atomic orbitals and they are most commonly associated with different nuclei. In brief, an electron in a molecule can be found anywhere in the molecule.

Molecular orbital theory alsoextendsthe valence bond theory. This two are the theories that are compatible for most of the bond formation and are able to explain the process of molecule placement as well. In case of molecular orbital theory the atomic orbitals of multiple atoms are being explained whereas the atomic orbitals are smeared out across the entire molecule.  This helps us to have an explanation of the electrons in an aromatic ring, and, in fact, helps us to predictwhether or notan aromatic ring will be more stable than the equivalent structure with isolated pibonds.

In the present trend, the molecular orbital theory is the basis for a number of quantum mechanical calculations. These calculations are carried out assuming that the electron wave function is a Linear Combination of Atomic Orbitals.

The formulation of the molecular orbital theory has paved a new way to understand the process of bonding.  With the application of this theory, it is being understood that the molecular orbitals are basically considered as linear combinations of atomic orbitals. The approximations are further carried out using the Harte–Fock (HF) or the density functional theory (DFT) models to the Schrödinger equation. These theories will also explain the nature of the molecule bond formation.

What are Molecular Orbitals?

 The molecular orbital function can be defined as the space in a molecule where there is a maximum probability of finding an electron.They are basically mathematical functions that describes the wave nature of electrons in a definite molecule.  The orbitals are constructed with the help of atomic orbitals derived from each atom that will be assigned to a specific molecule.  The molecular orbitals help us study this bonding between the molecules with the help of molecular orbital theory.

Types of Molecular Orbitals

 There are primarily three types of molecular orbitals that are formed from the linear combination of atomic orbitals. The details are explained below:

Anti-Bonding Molecular Orbitals

In this type of structurethe electron density is concentrated behind the nuclei of the two bonding atoms. As a result of this, the nuclei of the two atoms get pulled away from each other. These kinds of orbitals tend to weaken the bond between two atoms.

Non-Bonding Molecular Orbitals

In this type of orbital sequencing, due to a complete lack of symmetry in the compatibility of two bonding atomic orbitals, we will notice that the molecular orbitals that are formed have no positive or negative interactions with each other.These type of orbitals formed will not affect the bond between the two atoms.

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