Important Study Notes on Covalent Bonding

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Today we are sharing an article on Covalent bond and hybridisation. It is an important topic from the JEE Main examination point of view. The chapter 'Chemical Bonding' carries a good weightage in engineering entrance examinations. We are hoping that this article will help you to clear your doubts. 

Covalent Bond

Valence Bond Theory

Consider two atoms A and B approaching each other. As they approach towards each other, attractive forces arise between them:

• Nucleus of one atom and its own electron
• Nucleus of one atom and electron of other Atom.

Similarly, repulsive forces arise between

• electrons of two atoms
• nuclei of two atoms NA–NB.

Magnitude of new attractive force is more than the new repulsive forces. As a result, two atoms approach each other and potential energy decreases. Ultimately a stage is reached where the net force of attraction balances the force of repulsion and system acquires minimum energy.

Since the energy gets released when the bond is formed, the energy so released is called as bond enthalpy. Conversely, same energy is required to dissociate one mole of respective molecule.

Orbital Overlap Concept

The partial merging of atomic orbital’s at a minimum energy state is called overlapping of atomic orbital’s which results in the pairing of electrons. In general, greater the overlap the stronger is the bond formed between two atoms. Therefore, formation of a covalent bond between two atoms results by pairing of electrons present in the valence shell having opposite spins.

The valence bond theory explains the formation and directional properties of bonds in polyatomic molecules like CH4, NH3 and H2O, etc. in terms of overlap and hybridization of atomic orbital’s.

Types of Overlapping and Nature of Covalent Bonds

The covalent bond may be classified into two types depending upon the types of overlapping:

(i) Sigma Bond

This type of covalent bond is formed by the end to end (hand-on) overlap of bonding orbital’s along the internuclear axis.

(a) s-s overlapping

(b) s-p overlapping

(c) p–p overlapping

(ii) Pi(π) bond

In the formation of π bond the atomic orbital’s overlap in such a way that their axes remain parallel to each other and perpendicular to the internuclear axis.

In case of sigma bond, the overlapping of orbital’s takes place to a larger extent. Hence, it is stronger as compared to the pi bond.

Hybridisation

Pauling introduced the concept of hybridisation. According to him the atomic orbital’s combine to form new set of equivalent orbital known as hybrid orbitals. Unlike pure orbitals, the hybrid orbitals are used in bond formation. The phenomenon is known as hybridisation which can be defined as the process of intermixing of the orbital’s of slightly different energies so as to redistribute their energies, resulting in the formation of new set of orbitals of equivalent energies and shape.