Answer:
1.84 D, pointing to the O atom from the midpoint of the line joining the two H nuclei.
Step-by-step explanation:
(1) Direction
O is more electronegative than H, so an O_H bond dipole points from H to O along the bond axis.
There are two O-H bonds, so the net dipole points to the O atom from the midpoint of the line joining the two H nuclei (see diagram).
(2) Magnitude
The net dipole moment of water is the vector sum of the two O-H bond dipoles (1.50 D).
Consider the contribution from one O-H bond dipole.
The H-O-H bond angle of water is 104.5°.
Half that value is 52.25 °.
µ = 1.50(cos52.25°) = 1.50 × 0.6122 = 0.918
There are two bond dipoles, so the net molecular dipole is
µ = 2 × 0.918 D = 1.84 D
