Why Isn't Water on the Periodic Table?

A glass of water

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The periodic table of elements only includes individual chemical elements. Water is not found on the periodic table because it does not consist of a single element.

An element is a form of matter than cannot be broken down into simpler particles using any chemical means. Water consists of hydrogen and oxygen. The smallest particle of water is a water molecule, which is made of two atoms of hydrogen bonded to one atom of oxygen. Its formula is H2O and it can be broken down into its components, so it is not an element.The hydrogen and oxygen atoms of water do not contain the same number of protons as each other -- they are different substances.

Contrast this with a lump of gold. The gold can be finely subdivided, but the smallest particle, the gold atom, has the same chemical identity as all of the other particles. Each gold atom contains the exact same number of protons.

Water as an Element

Water was considered to be an element in some cultures for a very long period of time, but this was before scientists understood atoms and chemical bonding. Now, the definition of an element is more precise. Water is considered a type of molecule or compound.

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Helmenstine, Anne Marie, Ph.D. "Why Isn't Water on the Periodic Table?" ThoughtCo, Aug. 28, 2020, thoughtco.com/water-and-the-periodic-table-609434. Helmenstine, Anne Marie, Ph.D. (2020, August 28). Why Isn't Water on the Periodic Table? Retrieved from https://www.thoughtco.com/water-and-the-periodic-table-609434 Helmenstine, Anne Marie, Ph.D. "Why Isn't Water on the Periodic Table?" ThoughtCo. https://www.thoughtco.com/water-and-the-periodic-table-609434 (accessed June 2, 2023).