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Molecular Orbital Theory – Study Of Structure & Properties Of Molecules

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A molecular orbital is formed when the atomic orbitals overlap to form new orbitals. The molecular orbital theory is a technique explained in the twentieth century by R. S. Mulliken and F. Hund to describe the structure and properties of different molecules. The molecular orbital theory gives a method of understanding the composition of a molecule by using molecular orbitals of the individual atoms.

In the process of forming the molecule, the respective atoms combine with each other. The number of orbitals seen in the molecule is equal to the number of orbitals in the combining atoms. When 2 atoms combine with each other having one atomic orbital, 2 molecular orbitals are produced.

Molecular orbital theory can be demonstrated by analyzing diatomic molecules of compounds like H and He. The energy level representation is as shown below in the figure. Here each atom of hydrogen features one 1s electron. In the H 2 molecule, the 2 hydrogen electrons occupy the lowest energy level in the molecular orbital, the sigma orbital.

Molecular bond order is determined using the formula given below:

bond order = ½ (bonding electrons − antibonding electrons)

For hydrogen atoms

For the H 2 molecule, the bond order is given by

½ (2 − 0) = 1.

We can say that a single bond connects the 2 Hydrogen atoms in the Hydrogen molecule.

Let us know more about one of the chemical compounds which is thecarboxylic acid.

Carboxylic acid is an organic compound that occurs widely and features a carboxyl group (C(=O)OH). They are the unique compound that is identified by the suffix – oic acid in the chemical name.

They are identified by the presence of carbonyl carbon that is double bonded to one oxygen and singly bonded to a hydroxyl group. This means that the sp3 hybridization is seen for one oxygen atom and sp2 hybridization is seen in another oxygen atom. The hydrogen atom is attracted towards these oxygen atoms.

Saturated Carboxylic acid like formic acid is identified in insect sting, lauric acid is seen in coconut oil, carbonic acid is detected in the bicarbonate system of blood and tissues, acetic acid is found in Vinegar, butyric acid is present in butter,  palmitic acid is observed in palm oil, stearic acid is present in chocolate, waxes, soaps, and oils. Arachidic acid is witnessed in peanut oil. Hence we can say that Carboxylic acid compounds are naturally occurring.

The structural formula for Carboxylic acid is as shown below.

The carboxyl group ionizes and frees H atom present in the hydroxyl group part as a proton or a free H+ ion. Hence the remaining oxygen atom carries a negative charge. The charge moves in between the two oxygen molecules randomly making the state of ionization relatively steady.

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The relative vitality dimensions of nuclear and sub-atomic orbitals are regularly appeared in a sub-atomic orbital outline (Figure 8). For a diatomic particle, the nuclear orbitals of one iota are appeared on the left, and those of the other molecule are appeared on the right. Every level line speaks to one orbital that can hold two electrons.

Molecular Orbital Energy Diagrams

The sub-atomic orbitals shaped by the mix of the nuclear orbitals are appeared in the middle. Dashed lines show which of the nuclear orbitals join to frame the atomic orbitals. For each pair of nuclear orbitals that join, one lower-vitality (holding) sub-atomic orbital and one higher-vitality (antibonding) orbital outcome. Therefore we can see that joining the six 2p nuclear orbitals results in three holding orbitals (one σ and two π) and three antibonding orbitals (one σ* and two π*).

We foresee the circulation of electrons in these sub-atomic orbitals by filling the orbitals similarly that we fill nuclear orbitals, by the Aufbau guideline. Lower-vitality orbitals fill first, electrons spread out among ruffian orbitals before matching, and each orbital can hold a limit of two electrons with inverse twists.

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