The unequal sharing of electrons within a water molecule makes the water molecule _____.
Polar. Oxygen is far more electronegative than hydrogen, so it pulls the shared bonding electrons closer to itself. This gives oxygen a partial negative charge and each hydrogen a partial positive charge, making the bent water molecule an electric dipole, that is, polar.
The answer
The unequal sharing of electrons makes a water molecule polar. In each O–H bond, oxygen and hydrogen share a pair of electrons, but they do not share equally. Oxygen has a much stronger pull on electrons, its electronegativity is about 3.44 versus about 2.20 for hydrogen. Because oxygen tugs the shared electrons toward itself, the electron density piles up around the oxygen end and thins out around the hydrogens.
This uneven distribution creates partial charges: a partial negative charge (written delta-minus) on the oxygen and a partial positive charge (delta-plus) on each hydrogen. A molecule with separated regions of positive and negative charge is called a dipole, and having a net dipole is exactly what "polar" means.
Why the shape matters too
Unequal sharing alone creates polar bonds, but the molecule's bent shape is what makes the whole molecule polar. Water is not linear; its two O–H bonds sit at roughly a 104.5-degree angle because oxygen also carries two lone pairs of electrons that push the bonds down. Because the molecule is bent, the two bond dipoles do not cancel, they add up to point toward the oxygen. (In a symmetric linear molecule like CO2, equal and opposite bond dipoles cancel, leaving it nonpolar even though its bonds are polar. Water's bent geometry avoids this.)
Why not the other options
Common distractors on this question include:
- Nonpolar is wrong, that would require electrons to be shared equally (as in O2 or N2) or a symmetric shape that cancels the dipoles. Neither is true for water.
- Ionic / an ion is wrong. Ionic bonds involve the complete transfer of electrons, creating full +1 or -1 charges. Water only has partial charges from unequal sharing, so its bonds are polar covalent, not ionic. Water is a neutral molecule overall.
- A hydrogen bond is wrong as a description of the molecule itself. Hydrogen bonding is a consequence of water's polarity, an attraction between separate water molecules, not what a single molecule "is."
The bigger picture
Water's polarity is responsible for nearly all of its famous properties. The delta-plus hydrogens of one molecule are attracted to the delta-minus oxygens of neighboring molecules, forming hydrogen bonds. These bonds give water its high boiling point, high surface tension, and its ability to dissolve salts and other polar substances (making it the "universal solvent"). Polarity also explains why ice floats, why water climbs up plant stems (capillary action), and why oil and water do not mix. So a single concept, unequal electron sharing, cascades into the chemistry that makes life possible.
The unequal sharing of electrons within a water molecule makes the water molecule _____.
Frequently asked
Why is water a polar molecule?
Because oxygen is much more electronegative than hydrogen, it pulls the shared electrons in each O–H bond toward itself, creating a partial negative charge on oxygen and partial positive charges on the hydrogens. Water's bent shape prevents these bond dipoles from cancelling, so the whole molecule is polar.
What is electronegativity and how does it cause polarity?
Electronegativity is an atom's ability to attract shared bonding electrons. When two bonded atoms differ in electronegativity, the more electronegative atom pulls the electrons closer, creating partial charges. Oxygen's electronegativity (about 3.44) far exceeds hydrogen's (about 2.20), which is why the O–H bonds and the water molecule are polar.
How does water's polarity lead to hydrogen bonding?
The partial positive hydrogens of one water molecule are electrostatically attracted to the partial negative oxygen of a neighboring molecule. This attraction is a hydrogen bond. These bonds link water molecules together and produce water's high boiling point, surface tension, and cohesion.
Is water a polar or nonpolar molecule?
Water is polar. It has polar O–H bonds from unequal electron sharing, and its bent 104.5-degree shape means the bond dipoles add together instead of cancelling, giving the molecule a net dipole with a negative oxygen end and a positive hydrogen end.
What properties of water result from its polarity?
Polarity gives water its ability to dissolve salts and polar molecules (the universal solvent), high surface tension, cohesion and adhesion (capillary action), a high boiling point, and the fact that ice is less dense than liquid water. All of these stem from hydrogen bonding between polar water molecules.