Water is polar because it has polar covalent bonds and an asymmetrical, bent molecular shape. The oxygen atom in a water molecule is more electronegative than the hydrogen atoms, which means it attracts electrons more strongly. This uneven distribution of electron density creates partial negative charges near the oxygen and partial positive charges near the hydrogens. Because water's shape is bent (due to two lone pairs on oxygen), the partial charges do not cancel out, resulting in a molecule with distinct positive and negative ends, or poles. Thus, water is a polar molecule with a positive side and a negative side.
The polarity arises from two main factors:
- The difference in electronegativity between oxygen (3.5) and hydrogen (2.1) causes the O-H bonds to be polar covalent bonds.
- Water’s bent shape (about 106.5° bond angle) due to lone electron pairs on oxygen makes the molecule asymmetrical, so the dipole moments do not cancel each other out.
This polarity is responsible for many important properties of water, including hydrogen bonding and its ability to dissolve many substances.
