MOT Full Form

What is the Full Form of MOT?

The Robert S. Mullikan-created Molecular Orbital Theory uses the electrons' wave-like properties to describe bonding behaviour. According to the Molecular Orbital Theory, the bonding between atoms is modelled as a combination of their atomic orbitals. While Lewis Structures and the Valence Bond Theory can properly represent simple models, the Molecular Orbital Theory offers solutions to more challenging problems. The electrons are delocalized in the Molecular Orbital Theory. When electrons are not associated with a specific element or bond, they are said to be delocalized (as in the case of Lewis Structures). Instead, the molecule is covered in "smeared-out" electrons. The Molecular Orbital Theory makes it possible to anticipate how a molecule's electrons will be distributed, which can help determine molecular characteristics like structure, magnetism, and Bond Order.

Molecular Orbitals

It is a wave function of an electron in a molecule that is used to determine the chemical and physical characteristics of that molecule. The areas of a molecule where an electron can fill an orbital are found using a molecular orbital.

These orbitals may be constructed by combining hybridized or atomic orbitals from each element in the particular molecule.

Linear Combination Of Atomic Orbitals

A linear combination of atomic orbitals typically describes molecular orbitals (abbreviated to LCAO). These LCAOs help to estimate how these orbitals develop during the bonding between the atoms that compose a molecule.

An approach equivalent to that utilised for atomic orbitals can be used to write the Schrodinger equation to describe the behaviour of electrons in molecular orbitals.

It is a way of representing molecular orbitals that is easy to evaluate. It works more like a superimposition technique where the bonding molecular orbital is created by the constructive interference of two atomic wave functions. In contrast, the non-bonding molecular orbital is created by destructive interference.

Requirements for atomic orbital linear combination-

The following prerequisites must be met for an atomic orbital combination to be linear:

Same Energy Of Combining Orbitals

The molecular orbitals created when atomic orbitals combine ought to have similar energies. It indicates that while an atom's 2p orbital can connect with another atom's 2p orbital, 1s and 2p cannot combine because of their significant energy differences.

Same Symmetry About Molecular Axis

For a proper combination, the combining atoms must have the same symmetry around the molecular axis; otherwise, the electron density will be low, for example, All 2p sub-orbitals have the same energy, but because they have different symmetry axes, the 2px and 2py orbitals cannot be combined with the 2pz orbital of another atom. The z-axis is typically regarded as the axis of symmetry for molecules.

Proper Overlap Between Atomic Orbitals

If the overlap is correct, the two atomic orbitals will join to form a molecular orbital. The nuclear density between the two atoms' nuclei will increase in proportion to how much their orbitals overlap.

Two specific prerequisites help to clarify the condition. The right energy and orientation are necessary to form a proper molecular orbital. The two atomic orbitals should have the same significance for proper energy, and for proper orientation, the atomic orbitals should have the same molecular axis of symmetry and proper overlap.

Formation Of MOT

• The number of atomic orbitals the bonding species provides will always equal the total number of molecular orbitals created.

• Several molecular orbitals exist, including bonding, anti-bonding, and non-bonding molecular orbitals. This energy will always be higher for anti-bonding molecular orbitals than for the parent orbitals. In contrast, the energy of bonding molecular orbitals will always be lower than the parent orbitals.

• As the orbital energy increases, the electrons are filled into molecular orbitals (from the orbital with the lowest energy to the orbital with the highest energy).

• Atomic orbital pairings that produce molecular orbitals work best when the atomic orbitals involved have similar energies.

Bonding Molecular Orbitals

• Bonding molecular orbitals are molecule orbitals created by the additive impact of atomic orbitals.

• Bonding molecular orbitals enhance the probability of locating the electrons.

• These are formed when ‘+’ and ‘+’ and ‘-’ with ‘-’ portions of the electron waves combine.

• The bonding molecular orbital in the internuclear region has a significant electron density. Therefore, the atoms are protected from one another, resulting in very little repulsion.

• The orbitals of the bonding molecules are denoted by \sigma, \pi ,\delta

Anti-Bonding Molecular Orbitals

• Antibonding molecule orbitals are atomic orbitals created by the subtractive impact of atomic orbitals.

• In antibonding molecular orbitals, there is a lower probability of locating electrons. Additionally, there is a junction between the antibonding molecular orbitals of two nuclei with no electron density.

• These are created by the portion ‘+’ and ‘-’ portions of the electron waves overlapping.

• The nuclei are immediately exposed to one another because of the extremely low electron density in the antibonding molecular orbital in the internuclear region. Consequently, there is less shielding in between the nuclei.

• The anti-bonding molecular orbitals are denoted by \sigma ^{\ast },\pi ^{\ast },\delta ^{\ast }.

Sigma And Pi Bond

Hydrogen gas, the smallest molecule, exists as dihydrogen (H-H), which consists of two hydrogen atoms bound together by a single covalent link. The link is created by the overlap of these two atomic orbitals because each hydrogen atom only has one 1s atomic orbital for its electron. The two atomic orbitals are shown in the image on the left and right, respectively. The vertical line always represents the orbital energies. An electron is solely occupying each chemical orbital with an up- or down-arrow.

In the CO molecule, the carbon and oxygen atoms are joined by three covalent bonds and each has a lone pair of electrons in the spz hybrid orbital. The oxygen atom is smaller and more electronegative than the carbon atom. As a result, the orbitals of the oxygen atom are less energetic than those of the carbon atom. Both the oxygen and the carbon atoms undergo the spz bonding process.

Valence Bond Theory (VBT)

• Mono-centric orbitals characterise atoms.

• Atoms that participate in the creation of bonds retain their unique characteristics.

• VBT is convenient and clear.

• The resulting molecular orbital is created by combining the two wave functions of two single electrons.

• Some valence electrons in VBT are denoted as unshared and uninvolved in the molecule's creation.

• VBT did not adequately explain the paramagnetic behaviour of oxygen.

Molecular Orbital Theory (MOT)

• Poly-centric molecular orbitals exist.

• Atomic orbitals lose their unique characteristics when they merge to create molecular orbitals.

• MOT is complicated, particularly regarding molecules with more than two atoms.

• The LCAO approximation technique is used to form molecular orbitals. Only Atomic Orbitals with a Valence Shell of 2 are involved in creating Molecular Orbitals.

• According to the MOT technique, a molecule's atoms' valence shell electrons, all participate in bonding.

• MOT effectively describes oxygen's paramagnetic behaviour.