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# Explain Valance Bond Theory

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## Valence Bond TheoryIn a molecule, electrons inhabit atomic orbitals rather than molecular orbitals.It is based on the concept of bond overlapping.Covalent bonding is a chemical link generated by the sharing of electrons.Postulates:-When two valence orbitals present in two separate atoms overlap on one other, the covalent bonds are created.Due to this overlapping, the electron density between the two bonding atoms increases, increasing the stability of the resulting molecule.The valence shell of an atom has several unpaired electrons, allowing it to make many bonds with other atoms.According to the VBT, the paired electrons present in the valence shell do not participate in the creation of chemical bonds.Geometry of water molecule:The electronic configuration of the Hydrogen atom is $1{\mathrm{s}}^{1}$ and oxygen is $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{4}$.In water molecules, there are 2 oxygen atoms, and hence two half-filled $\mathrm{p}$-orbitals.Oxygen needs two more electrons to complete the octet and Hydrogen requires one more electron to acquire the configuration of $\mathrm{He}$.Two-half-filled orbitals of the two Hydrogen atoms separately overlap with one of the two half-filled $\mathrm{p}$-orbitals of the Oxygen atom.This gives rise to two single covalent bonds between the central atom and two Hydrogen atoms.The three $\mathrm{p}$-orbitals are along the three perpendicular axes in space.The valence bond theory of the water molecule describes the two $\mathrm{O}-\mathrm{H}$ bonds as resulting from the overlap of $1\mathrm{s}$ orbital of Hydrogen with the two half-filled $2\mathrm{p}$ orbitals of the oxygen atom.Since the two $2\mathrm{p}$ orbitals are at right angles to one another, valence bond theory predicts a bent geometry for the water molecule with a bond angle of $90°$.The $\mathrm{H}-\mathrm{O}-\mathrm{H}$ bond angle in water is $104.45°$and is having a bent tetrahedral geometry or V-shaped.The opening of the angle to a value greater than the predicted one of $90°$can be accounted as due to the repulsion between the two hydrogen nuclei.

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