Answer:
In Valence Bond Theory (VBT), the water molecule is formed by overlapping of two hydrogen 1s orbitals with two hybridized oxygen orbitals. The oxygen atom in the water molecule has two unpaired electrons in two 2p orbitals and two paired electrons in two 2s orbitals. It hybridizes the 2s and 2p orbitals to form four hybridized sp3 orbitals. These four sp3 hybridized orbitals point towards the corners of a tetrahedron.
The two hybridized orbitals of oxygen containing unpaired electrons overlap with the 1s orbitals of two hydrogen atoms. This overlapping results in the formation of two O-H sigma (σ) bonds. The two remaining hybridized orbitals containing the paired electrons do not participate in bond formation.
The bond angle in the water molecule is 104.5°, which is less than the tetrahedral angle (109.5°) because the two lone pairs of electrons on the oxygen atom exert greater repulsion than the two bonding pairs. This causes the bonding pairs to be pushed closer together, resulting in a smaller bond angle.