Characteristics of Anti-bonding Molecular Orbitals

The valence bond hypothesis is an extended part of Lewis Structures that considers orbital overlaps to form bonds. However, the valence bond hypothesis has a restricted application since it does not adequately describe molecular geometry. It is where the MOT (molecular orbital theory) comes into play. According to this theory, the atomic orbitals unite and generate molecular orbitals. The molecular orbitals are segregated into non-bonding, bonding and antibonding molecular orbitals. The below article will discuss the antibonding molecular orbitals definition along with the characteristics of bonding and antibonding orbitals in detail. 

Molecular Orbitals

Molecular orbitals (MOs) are acquired by the merging of atomic orbitals on the atoms in a molecule.  In chemistry, a molecular orbital is a mathematical function that specifies the location of an electron in a molecule. A molecular orbital can calculate physical and chemical factors like the probability of finding an electron in a specific location. It also depicts the wave-like behaviour of electrons. A molecular orbital is filled when it has two electrons with opposing spins, similar to atomic orbitals.

The region of space where a molecule’s valence electron is most usually present is known as a molecular orbital. They can be classified into three types, namely non-bonding, bonding and antibonding molecular orbitals. First, let’s look into the antibonding molecular orbitals definition. 

Antibonding molecular orbitals definition

The molecular orbitals in which the density of electrons is spread exterior to the bonding region are called antibonding molecular orbitals (ABMOs). The antibonding molecular orbitals definition also states that these orbitals are created by the subtractive action of the electrons of the merging atomic orbitals. 

The energy of antibonding molecular orbitals is usually higher than that of bonding molecular orbitals. When atoms join to create molecules, bonding and antibonding orbitals are formed. When 2 atoms of hydrogen are separated by a large distance, their atomic orbitals are identical. The electron wave functions start overlapping as the distance between these two atoms decreases. Any 2 electrons in a molecule cannot have the same set of quantum numbers, according to Pauli’s exclusion principle. As a result, each isolated atom’s initial atomic orbital splits into 2 molecular orbitals, one with energy lesser than the parent atomic level and the other with higher energy.

The bonding orbital possesses lower energy than the parent atomic orbitals, making it more stable and promoting the combining of the 2 Hydrogen atoms into H₂. According to the antibonding molecular orbitals definition, the ABMO is the higher-energy orbital that is less stable and resists bonding when occupied. The two electrons in a molecule like H₂ take up the low-energy bonding orbital, making the molecule more stable than the individual H atoms.

Antibonding molecular orbitals: characteristics

The antibonding molecular orbitals’ properties are as follows:

• The antibonding molecular orbitals’ electrons lead to the repulsion between the two atoms. 
• Antibonding molecular orbitals possess greater energy and less stability due to repulsive forces.
• The likelihood of locating electrons in the internuclear region reduces in antibonding molecular orbitals.
• They are created by the subtractive impact of atomic orbitals.
• When the density of electrons in the internuclear region is less, a molecular orbital is said to be antibonding. 
• The spatial configuration of ABMOs doesn’t represent molecular shape or geometry. 
• When a molecular orbital alters the sign from +ve to -ve in the nodal plane between the 2 parent atoms, that orbital is referred to as antibonding with respect to the 2 atoms.
• On molecular orbital diagrams, antibonding orbitals are frequently marked with an asterisk (*).

Bonding molecular orbitals: what are they?

The Bonding molecular orbitals or BMO are created when 2 atomic orbitals from 2 separate atoms overlap. This overlapping causes both the atomic orbitals to mix and produce these molecular orbitals. The BMOs have a higher density of electrons than ABMOs. 

Bonding molecular orbitals: characteristics

The bonding molecular orbital has certain properties, which are as follows:

• The two participating atoms are attracted to one another because of the bonding molecular orbital electrons.
• They play a vital role in forming chemical bonds. 
• The BMOs form due to the atomic orbitals’ additive influence.
• The likelihood of locating the electron in the internuclear area of the bonding molecular orbital or BMO is higher than that of merging atomic orbitals.
• The BMOs have lesser energy and better stability than the merging atomic orbitals.
•  The BMOs aid in the determination of molecular geometry.  

Conclusion

The merging of the atomic orbitals to produce new molecular orbitals is the subject of the molecular orbital hypothesis. These new orbitals are formed by combining atomic orbitals in a linear fashion to generate bonding and antibonding orbitals. Since bonding orbitals have lower energy than antibonding orbitals, they fill up first. It is simple to work out bond order by determining the molecular orbitals. The above article briefly discusses the antibonding molecular orbitals definition and the characteristics of bonding and antibonding molecular orbitals.