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The development of a covalent bond between two atoms is caused by the pairing of electrons in the valence shell with opposing spins, according to the orbital overlap principle. Bond formation might be caused by orbital overlap. When two atoms reach close enough to one another during the orbital process, they pierce each other’s orbital, establishing a new hybridised orbital wherein the electron’s bonding pair resides.
As it has lower energy as compared to the atomic orbital, a hybridised orbital is stable. It’s in its lowest energy condition. Orbital overlap is the partial penetration of one orbital to generate a new hybridised orbital.
What Is The Extent Of Overlap?
The number of interacting atoms, their mass, and their valence electrons determines the degree of overlap. In addition, the stronger the link created between the two atoms is, the higher the overlap. As a result, the orbital overlap hypothesis describes how atoms interact by overlapping their orbitals, resulting in a lower energy state where their valence electrons link up to form covalent bonds.
Types of Orbital Overlap Covalent Bond
There exist two types of orbital overlapping of covalent bonds, based on the structure of the overlap:
Sigma (σ) Bond
The end-to-end overlap of bonding orbitals throughout the internuclear axis forms the sigma bond. A head-on overlap, also known as axial overlap, is also the name of this overlap. There are three forms of axial overlap between these orbitals:
- s-s overlapping: Two half-filled s-orbitals overlap on the internuclear axis in this situation.
- s-p overlapping: This form of overlapping happens when one atom half-filled partially filled (50%) s-orbitals overlap with another atom’s partially filled (50%) p-orbitals.
- p-p overlapping: This sort of overlapping occurs when the two converging atoms’ p-orbitals are half-filled.
Pi (π) Bond
When atoms overlap in a manner that their axes stay parallel to one another and transverse to the internuclear axis, a pi (π) bond is produced. A sideway overlap is also the term for this form of overlap.
Difference Between Sigma And Pi Bond
Sigma Bond | Pi Bond |
Head-on-head overlapping of hybrid orbitals forms the sigma bond. | The overlapping of hybrid orbitals below and above the bonding axis forms the pi bond. |
The sigma connection is extremely strong and long-lasting. | The pi connection is brittle and unstable. |
Whenever two molecules or atoms engage with each other, the initial step is the development of a sigma bond. | Following the development of the sigma bond, the pi bond is formed. |
Typically, the sigma bond is represented by the sign σ. | Typically, the pi bond is represented by the sign π. |
Sigma bonds occur in alkanes, alkenes, and alkynes. | Pi bond formation does not occur in alkanes (saturated molecules). Pi bonds arise in unsaturated chemicals such as alkenes and alkynes. |
Comparing VB and MO
The Valency Bond (VB) theory states that electron pairs are confined between two particular atoms in a molecule that complements the molecular orbital (MO) hypothesis. However, the MO concept does not follow the VB principles entirely. According to the MO theory, electrons are scattered in molecular orbitals and can encompass the whole molecule. In a straightforward approach, the MO theory can determine magnetic and ionisation characteristics. The VB theory provides comparable findings, but it is more difficult to understand.
Overlapping of Atomic Orbital
Interaction of atoms creates different types of bonds. In nature, the charge in these bonds may be positive, neutral or negative. It depends on the signature and orientation of the respective two interacting orbitals.
- Positive Atomic Orbital Overlapping
When the phases of two engaging atomic orbitals are the same, the overlap is positive, and covalent bonding occurs. The phase of two interacting orbitals (+ or -) is determined by the signature of the orbital wave function and has no bearing on energy.
- Atomic Orbital Negative Overlapping
While two connected orbitals are in a phase opposite each other, the overlap produced is negative, and no connection is created.
- Atomic Orbital Overlap Is Null
A condition of zero overlapping of an atomic orbital occurs if two interacting orbitals in an orbital do not overlap one another.
Hybridisation
When atoms in a molecule are bonded together, the wave functions work together to create suitable mathematical representations with varied forms. Hybridisation is the process of merging the wave functions concerning atomic orbitals. Hybridisation is the process of combining orbitals with somewhat varying energies to redistribute its energy and create a new set of orbitals with comparable shapes and energies. Hybridisation can have three forms:
- sp hybridisation: The valence s orbital is mixed into a single valence p orbitals to produce two similar sp hybrid orbitals in the sp hybridisation process.
- sp2 Hybridisation: A group of three sp2 hybrid orbitals and a single unhybridised p orbital make up the valence orbitals of a core atom encircled by three zones of electron density.
- sp3 Hybridisation: The hybrids are created by combining one s orbital with all three p orbitals. An atom’s valence orbitals are made up of four sp3 hybrid orbitals that are enclosed in a tetrahedral configuration of bond pairings and lone pairs.
Conclusion
Chemical bonds are made up of forces that hold up atoms. Covalent bonds, ionic bonds, coordinate bonds, and hydrogen bonds are the four types of chemical bonding. The connections created by the transfer of electrons over two atoms are known as covalent bonds. A molecular bond is another name for it. In order to achieve stability, atoms unite to lessen the total energy. Simply said, the rule states that the less energy one needs, the simpler it is to survive. In this orbital overlap study material, we have talked about covalent bonds, sigma and pi bonds.
