Need of Hybridization During Formation of Water Molecule:
In oxygen atom there are two half – filled 2p orbitals and valency should be 2 and it is two. These three ‘p’ orbitals are perpendicular to each other and if they form bonds, the angle between them should be 90°. But actual angle between bonding orbitals in water is 104.5°. To explain this variation the concept of hybridization is required.
Atomic number of Oxygen is 8. Its configuration in ground state is 1s2, 2s2, 2p4
In the formation of water molecule one 2s orbital and three 2p orbitals of Oxygen mix up forming four hybrid orbitals of equivalent energy. These four new equivalent orbitals are called sp3 hybrid orbitals.
They are identical in all respect. Two hybrid orbitals have paired electrons and they are non – bonding orbitals. Other two orbitals are half – filled and they are bonding orbitals. The nonbonding pairs of hybridized orbitals are called as lone pairs.
These hybridized orbitals are in the directions of four corners of a regular tetrahedron.
Angle and Geometry of Water Molecule:
Four sp3hybridised orbitals formed, repel each other and they should be directed towards the four corners of a regular tetrahedron and Angle between them should be 109.5°. But due to greater repulsion exerted by lone pair on bonding orbitals, angle is reduced to 104.50. Thus water has distorted the tetrahedral shape.
The two half filled (containing unpaired electron) sp3 hybrid orbitals of oxygen overlap axially with two half filled 1s orbitals of two hydrogen atoms separately to form three O-H bonds.
Thus geometry is angular or V-shaped, in which the oxygen lies at the centre, two hydrogen atoms occupy two corners of the etrahedron and lone pair of electrons occupy remaining two corners of the tetrahedron. H-O-H angle is 104.50.
Bonds in Water Molecule:
The two half filled (containing unpaired electron) sp3 hybrid orbitals of oxygen overlap axially with two half filled 1s orbitals of two hydrogen atoms separately to form two O-H bonds (sigma bond). The remaining two hybrid orbitals containing a lone pair of electron remains nonbonded.