In molecular polarity, the dipole moment of a water (H2O) molecule has its negative end located in which direction within the molecule?

Introduction / Context:
Water is one of the most important examples used to illustrate molecular polarity. The bent shape and the electronegativity difference between oxygen and hydrogen give water a permanent dipole moment. This polarity affects many properties of water, including its high boiling point, surface tension and ability to dissolve ionic and polar substances. The question asks you to identify where the negative end of the dipole moment is located in a water molecule.

Given Data / Assumptions:

• Molecule: H2O, with one oxygen atom and two hydrogen atoms.
• The H–O–H bond angle is about 104.5 degrees, giving a bent geometry.
• Oxygen is more electronegative than hydrogen.
• Dipole moment has a direction from positive to negative charge centre.

Concept / Approach:
The concept is that electronegativity differences in a covalent bond create partial charges. In H2O, each O–H bond is polar, with electrons more attracted toward the oxygen atom. The molecular geometry is bent, not linear, so the individual bond dipoles do not cancel. As a result, the overall dipole moment vector points toward the region of higher electron density, near the oxygen atom. The negative end of the dipole is associated with the atom that carries a partial negative charge due to attracting bonding electrons more strongly.

Step-by-Step Solution:
Step 1: Recognise that oxygen has a higher electronegativity than hydrogen, so in each O–H bond, electrons are drawn closer to the oxygen. Step 2: As a result, oxygen carries a partial negative charge, while each hydrogen carries a partial positive charge. Step 3: The H2O molecule is bent, not linear, so the dipoles of the two O–H bonds add rather than cancel. Step 4: The combined dipole moment points toward the more negative region near the oxygen atom. Step 5: Therefore, the negative end of the dipole moment is directed toward the oxygen atom, with the positive region near the hydrogens.

Verification / Alternative check:
This conclusion can be verified by looking at electrostatic potential maps of water, which show a region of more negative potential around the oxygen atom. Experimental measurements of dipole moments confirm that water has a relatively high dipole moment among small molecules. Textbook diagrams usually draw the dipole arrow pointing toward the oxygen with a plus sign near the hydrogen side, consistent with this explanation. Water behaviour as a polar solvent, able to dissolve salts by interacting with cations and anions, further supports the idea that oxygen is the negative end.

Why Other Options Are Wrong:
Option B is wrong because the negative charge is not localised on just one hydrogen; hydrogens are partially positive, not negative. Option C incorrectly places the negative region between hydrogens, whereas that region is comparatively positive. Option D claims that there is no dipole, which would only be true if the molecule were linear or symmetrical with cancelling bond dipoles, which is not the case for water. Option E suggests the negative end is away from oxygen, which contradicts electronegativity considerations. Only option A correctly states that the negative end of the water dipole is toward the oxygen atom.

Common Pitfalls:
One common mistake is to assume that because water has two hydrogens, the negative region must be between them, but geometry and electronegativity must both be considered. Another pitfall is confusing the direction of dipole arrows; some conventions draw arrows from positive to negative, while others do the reverse. To avoid confusion, focus on which atom is more electronegative and therefore carries the partial negative charge. For water, remember that oxygen is the more electronegative atom and thus is associated with the negative end of the dipole.

Final Answer:
The negative end of the dipole moment in water is Toward the oxygen atom, which carries a partial negative charge due to its higher electronegativity.