Water Molecular Formula

Know the Molecular Formula or Chemical Formula for Water

This is the three-dimensional molecular structure of water.
This is the three-dimensional molecular structure of water. Laguna Design / Getty Images

The molecular formula for water is H2O. One molecule of water consists of one oxygen atom which is covalently bonded to two hydrogen atoms.

There are three isotopes of hydrogen. The usual formula for water assumes the hydrogen atoms consist of the isotope protium (one proton, no neutrons). Heavy water is also possible, in which one or more of the atoms of hydrogen consists of deuterium (symbol D) or tritium (symbol T). Other forms of the chemical formula of water include: D2O, DHO, T2O, and THO. It's theoretically possible to form TDO, although such a molecule would be extremely rare.

Although most people assume water is H2, only completely pure water lacks other elements and ions. Drinking water usually contains chlorine, silicates, magnesium, calcium, aluminum, sodium, and trace amounts of other ions and molecules.

Also, water dissolves itself, forming its ions, H+ and OH-. A sample of water contains the intact water molecule along with hydrogen cations and hydroxide anions.