Which of the following best represents the overall molecular dipole moment of a water (H_2O) molecule using a vector arrow?

• A. A single arrow pointing from the oxygen atom toward the midpoint between the two hydrogen atoms.
• B. Two arrows pointing from each hydrogen atom toward the oxygen atom.
• C. No arrow, because water has no net dipole moment.
• D. A single arrow pointing from the midpoint between the hydrogen atoms toward the oxygen atom.

Answer: (A)

Verified step by step guidance

1. Understand that the dipole moment in a molecule arises from differences in electronegativity between atoms, causing partial charges and a separation of charge.
2. Recognize that in a water (H_2O) molecule, oxygen is more electronegative than hydrogen, so the electron density is pulled toward the oxygen atom, creating a dipole moment pointing toward oxygen.
3. Recall that the molecular dipole moment is a vector sum of the individual bond dipoles; since water has a bent shape, the two O-H bond dipoles do not cancel but combine to give a net dipole.
4. Visualize the net dipole moment as a single arrow pointing from the midpoint between the two hydrogen atoms toward the oxygen atom, indicating the overall direction of electron density shift.
5. Conclude that the best representation is a single arrow pointing from the midpoint between the hydrogen atoms toward the oxygen atom, showing the net dipole moment direction.