A molecule of water consists of two hydrogen atoms joined to an oxygen atom by covalent bonds. The oxygen atom has six electrons (1s2 2s2 2p4) in its outermost shell. The 's' and 'p' orbital of the valence shell are sp hybridized to form four sp3 hybrid orbital oriented tetrahedrally around the oxygen atom. Two of the hybrids orbitals are singly occupied, while the lone-pairs of electrons occupy the other two. Each singly occupied sp3 orbital overlaps with the half-filled 1s orbital of 'H' atom.
Thus, oxygen is bonded to the two hydrogen atoms by two O-H covalent bonds, and there are two lone-pairs of electrons on the oxygen atom. Due to the presence of two lone-pairs of electrons on the O atom, the H-0-H bond angle is 104.5°, which is slightly less than the tetrahedral angle of 109°28′. Therefore, the structure of water molecule is an angular or bent structure. Oxygen is more electronegative than hydrogen; its high electronegativity causes the oxygen atom to pull the shared pairs of electrons more towards itself. As a result, the O-H bond acquires polarity. The actual dipole moment of water molecule is 1.84 Debye, (denoted as D) is the unit of dipole moments.
