Important Theories on Chemical Bonding

Important Theories on Chemical Bonding

Understanding the concept of chemical bonds is considered the most basic and crucial knowledge when studying the subject of chemistry. In this article, we shall discuss some important theories on chemical bonding to know how it works.

Valence bond theory

Valence bond theory was proposed to explain chemical bonds/molecules’ formation scientifically. It is based on atomic orbitals and the electronic configuration of atoms. It states that “electrons of any molecule attempt to occupy atomic orbitals instead of molecular orbitals by the process of hybridisation.” The bond strength of the chemical bond formed depends on the overlap; the greater the overlap, the stronger the bond strength of the molecule. 

Here are the two types of overlapping orbitals: 

Sigma

• Overlapping around the internuclear axis is called axial overlapping. Example: C-H bond or C-X bond.
• End-to-end overlap takes place.
• One head to another overlap.

Pi

• This is the sidewise overlapping of two unhybridized orbitals. Example: C=O bond.
• Overlaps perpendicular to the internuclear axis.
• Lateral overlap.

VSEPR theory

Valence Shell Electron Pair Repulsion theory or better known as the VSEPR theory, is one of the molecular structure models that is used to predict the structural geometry of molecules in chemistry. This is done by putting up a central atom and then surrounding them with single electron pairs that help complete the octets for the central and attaching atoms, thus achieving a balanced state.

While strong bonds are created, this results in a phenomenon called electron-electron repulsion, which occurs due to the same charge repulsion in the valence electron of the molecule formed. This typically results in a unique geometric arrangement among the atoms, which decreases the overall energy of the molecule formed. The geometries of molecules vary depending on the number of lone pairs in that molecular structure, as they are ultimately responsible for the repulsion in the valence electrons.

Here are some geometries according to the number of electron groups and lone pairs of electrons in a molecule:

Electronic theory of chemical bonding

This theory, proposed independently by Kossel & Lewis, states that a chemical bond is formed between atoms to get the nearest inert gas configuration. This can be achieved by either losing electrons, gaining electrons, or sharing electrons.

This theory of chemical bonding helps us with a better understanding of the structure and behaviour of atoms and molecules. This theory is an electronic theory, which means that it tries to explain chemical bonding in terms of the motions of the electrons within the atoms and molecules. 

The theory of chemical bonding makes predictions about how the structure of molecules and the properties of materials are related to the way the electrons are arranged within them. The theory of chemical bonding is a widely accepted scientific theory and has allowed for a wide range of predictions to be made about the world around us and to develop technologies such as drugs, plastics, and solar cells.

Molecular orbital theory

As per the Molecular Orbital Theory, the overlay of atomic orbitals forms molecular orbitals. It further states that electronegative atoms clutch electrons more securely and overcast their energies, which coincides with atomic orbital energy. This results in atomic orbitals having similar energies. Molecular Orbital Theory modelling is valid; whenever the energies differentiate substantially, the combining mode should be ionic, and overlapping atomic orbitals should have the same symmetry.

Depending on their phase connection, two atomic orbitals can overlay in two methods. The wave-like formation of electrons determines the phase of an orbital. The orbital phase is portrayed in graphical depictions of orbitals by a minus or plus sign (without relation to electrical charge) or with shading lobe one. The phase sign has no physical significance, except for when a combination of orbitals generates molecular orbitals. A constructive overlap occurs when two same-sign orbitals create a molecular orbital, with the quantity of the electron density positioned connecting the two nuclei. The connecting orbital has lower energy than the initial atomic orbitals.

Conclusion

We learnt about the Important Theories on Chemical Bonding and its essential features in this article. We have seen how valence bond theory helps in covalent bond formation. Also, we have learned about VSEPR Theory with the Molecular Orbital Theory. We also concluded and related the valence bond theory with the complex coordination compounds and their drawbacks.