Why Are Antibonding Orbitals Higher In Energy?

The molecular orbital theory is a theory that throws light on the chemical bonding of different atoms in a molecule. The layering causes the mixing of any two orbitals which results in the formation of a molecular orbital. These molecular orbitals are further divided into two branches namely bonding molecular orbital and antibonding molecular orbital. In this article, we will study the facts and differences between bonding molecular orbital and antibonding molecular orbital.

Bonding And Antibonding Molecular Orbitals

An antibonding molecular orbital is specified by electrons outside the region between the nuclei. Due to the electron orbital overlap, which creates a molecular bond between atoms. Thus, it is impossible for the electrons present in an orbital to have a similar non-relativistic state. Antibonding orbitals are signified by an asterisk symbol (*). Most of the electron density antibonding molecular orbitals are located away from the bonding area and try to pull a single nucleus out of the other which causes mutual repulsion. 

When we talk about anti-bonding orbitals the word ’star’ is very often written in the last orbital. The term sigma anti-bonding molecular orbitals are very often denoted by σ*. In sigma star antibonding molecular orbitals, the orbitals are mostly empty, but in cases where they must be occupied, the nature of the wave of electron density is entirely out of phase and is nullifying in nature.

On the other hand, bonding molecular orbitals are the ones that are often noticed to be involved in the formation of a certain chemical bond. These orbitals are known to be created in a process where two different atoms are overlapped by two different atomic orbitals. 

The result of these two given atomic orbitals is the inevitable formation of the molecular orbital. To attain results like this both the day atomic orbitals must have very similar symmetry and energy. These types of molecular orbitals (bonding molecular orbital) carry more electron density as compared to that in the antibonding molecular orbital. 

The energy that is stored in bonding molecular orbital is lesser, which makes them more stable than antibonding molecular orbital. Adding further, the bonding molecular orbital provides a huge contribution to molecular geometry. The spatial settlement of these orbitals determines the shape of a certain molecule. These few factors that tell us the difference between bonding molecular orbital and antibonding molecular orbital help us get a better knowledge about them.

Why are antibonding orbitals higher in energy?

Since the orbitals have decreased electron density between their nuclei which leads to stronger repulsion, and thus, the energy in the antibonding orbitals is said to be higher than those of bonding orbitals of the same level. Moreover, it is also said that the antibonding orbitals are out of phase which leads to more energy in them.

Difference between bonding and antibonding orbitals

Now you may have a brief idea about the difference between bonding molecular orbital and antibonding molecular orbital. To learn more about them we need to study them side-by-side:

• The very basic difference is that bonding molecular orbitals are responsible for the creation of a chemical bond, whereas anti-bonding molecular orbital theory electrons are outside the range of two given atomic nuclei. This is the first difference between bonding molecular orbital and antibonding molecular orbital.

• The second difference is that the energy carried by bonding molecular orbitals is comparatively lower than antibonding molecular orbitals. this is why the stability of bonding molecular orbitals is higher in comparison to antibonding molecular orbitals
• Lower energy, better stability, and higher electron density is seen in the bonding molecular orbital whereas higher energy, lower stability, and lower electron density antibonding molecular orbital are seen.
• Bonding molecular orbitals are not represented by an asterisk mark and their geometry is represented by a spatial arrangement whereas anti-bonding molecular orbitals are represented by an asterisk mark and their geometry doesn’t rely upon any type of spatial arrangement.

Now you must have a good idea about the difference between bonding molecular orbital and antibonding molecular orbital. 

Conclusion

Now we know that the molecular orbital theory is a theory that focuses on and explains the creation of various chemical bonds between different atoms due to layering or overlapping or due to mixing of certain atomic orbitals. The mixture that is created when is rice to new orbitals that we know have molecular orbitals. Moreover, we now know why antibonding orbitals have higher energy compared to bonding orbitals.

We see that these molecular orbitals can be divided into two categories that are bonding molecular orbital and antibonding molecular orbital. We learned many differentiating factors between them including the difference in shape, energy, density, and stability. The difference between bonding molecular orbital and antibonding molecular orbital helps us get a better insight into the topic.