The idea
Oxygen carries a partial negative charge and the hydrogens carry partial positive charges. These are partial charges, not full ionic charges. The attraction between the hydrogen of one water molecule and the oxygen of another forms a hydrogen bond. Hydrogen bonds between molecules help explain water’s cohesion and thermal properties; the O–H bonds inside each molecule are covalent.
Worked example
Explain why a water molecule can form hydrogen bonds with neighbouring water molecules.
- Unequal electron sharing creates partial charges.
- A partially positive hydrogen is attracted to a partially negative oxygen on another molecule.
- This intermolecular attraction is a hydrogen bond.
A mistake to avoid
Do not describe the bond between oxygen and hydrogen within a water molecule as a hydrogen bond. It is a polar covalent bond.
Check your understanding
Why is the shape of a molecule important when deciding whether it is polar?
Show the explanation
Bond dipoles can cancel in some symmetrical arrangements. Water’s bent shape means its bond dipoles give a net dipole.
Explore the lesson
This guide connects to Why water is a polar molecule in the IB Biology course. The first two published lessons per subject are free previews; further interactive lessons require an account.