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Sunday, 21 April 2013

VALENCE BOND THEORY

According to valence bond theory, four unpaired electrons are required to form four covalent bonds. But there are only 2 unpaired electrons in the valence shell of carbon in the ground state.
However it is possible to get 4 unpaired electrons by transferring one of the electrons from 2s orbital into the empty 2p orbital. This process is called excitation and carbon is said to be in the excited state. Now the electronic configuration of carbon in the excited state becomes 2s12p3.
A small amount of energy, which is available during the chemical bond formation, is sufficient for a carbon atom to undergo excitation.
excitation of carbon atom
It is now possible for carbon atom to form 4 bonds in the excited state.
However, carbon undergoes hybridization before forming actual chemical bonds with other atoms.
Hybridization is the process of intermixing of two or more pure atomic orbitals of almost same energy to form same number of identical and degenerate new orbitals known as hybrid orbitals.
The carbon atom can undergo three types of hybridizations i.e., sp3 or sp2 or sp

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