What atoms make up water and how many of each are there?

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Borys Shumyatskiy eNotes educator| Certified Educator


One molecule of water is made up of:

one atom of oxygen (`O` )


two atoms of hydrogen (`H` ).

The formula is therefore `H_2 O.`

The mass of one oxygen atom is about 16 times the mass of one hydrogen atom, so oxygen atom takes about `16/18 approx 89%` of water molecule's mass.

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