Explain the structure of water

Structure of Water Molecule

In water molecule, the oxygen is sp³ hybridized and hence has 4 sp³ hybridized orbitals. Two of these sp³ orbitals are half filled and hence overlap with 1s orbital of hydrogen to form two sp³ -s , O-H , σ bond while the other two contain a lone pair of electrons each.

The geometry of water molecule should be tetrahedral and the bond angle ∠HOH should be 109.5° but experimentally it has been determined that the actual bond angle is 104.5°.

Reason:

In water, the oxygen atom is surrounded by two shared pair ,and two lone pair of electrons. According to valence shell electron pair repulsion theory, lone pair- lone pair repulsion are stronger than Bond pair – Bond pair repulsion. As a result the bond angle in water is slightly smaller than the regular tetrahedral angle of 109.5°.The actual bond angle is 104.5° and each O-H  bond has a bond length of 95.7pm.

In the gaseous state, water exist as discrete molecules. It is a bent molecule with bond angle of 104.5° and bond length of 95.7 pm.

The electronegativity of oxygen is much higher than that of hydrogen and hence the shared pair of electrons in O-H bonds are attracted slightly more towards the oxygen atom. As a result oxygen carries a partial negative charge and hydrogen atoms carrier a partial positive charge. Since these two dipoles are inclined to each other at an angle of 104.5° therefore water is a highly polar molecule its actual dipole moment is 1.84 D.