Water's polarity arises from two key factors: the unequal sharing of electrons between oxygen and hydrogen atoms and the bent molecular shape.
Unequal Electron Sharing
Oxygen is more electronegative than hydrogen. This means oxygen attracts electrons more strongly in the covalent bonds forming the water molecule (H₂O). This unequal sharing creates a slightly negative charge (δ-) near the oxygen atom and slightly positive charges (δ+) near the hydrogen atoms. As stated by multiple sources including this article from manoa.hawaii.edu, "The unequal sharing of electrons between the atoms and the unsymmetrical shape of the molecule means that a water molecule has two poles - a positive charge on the hydrogen pole (side) and a negative charge on the oxygen pole (side)." This charge separation is what makes the molecule polar. The American Chemical Society also highlights the importance of the O-H bonds in creating this polarity: https://www.acs.org/middleschoolchemistry/lessonplans/chapter5/lesson1.html.
Bent Molecular Shape
The water molecule isn't linear; it has a bent shape. This arrangement further enhances the polarity by preventing the positive and negative charges from canceling each other out. The slightly positive hydrogen ends are clustered on one side, and the slightly negative oxygen is on the opposite side. This asymmetrical distribution of charge is crucial for water's polarity. As noted by Study.com, "Water is a polar molecule due to the unequal distribution of its electron density."
Consequences of Water's Polarity
Water's polarity is responsible for many of its unique properties, including:
- High boiling point
- Excellent solvent for polar substances
- High surface tension
- Cohesion and adhesion
In summary, the combination of unequal electron sharing and the bent molecular geometry creates a dipole moment, making water a polar molecule.
