Which compound has the molecular formula H₂O?

The compound with the molecular formula H₂O is water.

Each water molecule contains two hydrogen atoms covalently bonded to one oxygen atom. The bonds and the molecule’s bent shape make water polar: the oxygen side carries a partial negative charge, while the hydrogen side carries a partial positive charge.

Polarity gives water several unusual properties. Water molecules form hydrogen bonds, producing relatively high surface tension, a high boiling point for such a small molecule, and the expansion of liquid water as it freezes. Ice is less dense than liquid water, so it floats.

Water is often called the universal solvent, but that phrase is not literal: it cannot dissolve every substance. It dissolves many ionic and polar compounds and is central to Earth’s climate, geology, biology, and chemistry. Pure water at standard pressure freezes at 0°C and boils at 100°C.