What characteristic of water allows it to form hydrogen bonds?

Water's ability to form hydrogen bonds is primarily due to its polarity. In a water molecule, the oxygen atom is more electronegative than the hydrogen atoms, which leads to an uneven distribution of electron density. This causes the oxygen atom to acquire a partial negative charge while the hydrogen atoms have partial positive charges.

The polar nature of water results in the formation of hydrogen bonds, which are weak attractions between the positively charged hydrogen atoms of one water molecule and the negatively charged oxygen atoms of adjacent water molecules. This significant characteristic of water is crucial for various biological processes, including its role as a solvent, its high specific heat, and its ability to stabilize temperatures in living organisms.

This fundamental property of water contrasts with other characteristics such as viscosity, molecular size, and density, which do not directly influence the formation of hydrogen bonds or the unique properties that arise from them.