Britannica Sources used in this answer

Why does oxygen have a partial negative charge in a water molecule?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

water rapids, Niagara Falls, Canada — water Water is the most plentiful compound on Earth and is essential to life. Although water molecules are simple in structure (H₂O), the physical and chemical properties of water are extraordinarily complicated.

In a water molecule, the oxygen atom acquires a partial negative charge due to its higher electronegativity compared to the hydrogen atoms.12

Electronegativity is defined as the ability of an atom to attract shared electrons toward itself when participating in a chemical bond. Although the oxygen and hydrogen atoms share electron pairs to form covalent bonds, the oxygen atom exerts a stronger pull on these shared electrons. By drawing the shared electron density closer to its own nucleus, the oxygen atom effectively gains a greater share of the negative charge, resulting in a partial negative charge ( $δ -$ ), while the hydrogen atoms are left with a partial positive charge ( $δ +$ ).132

This unequal distribution of charge creates a polar bond, and because the water molecule is bent rather than linear, these bond dipoles do not cancel out, giving the entire molecule a nonzero dipole moment.12