Chemistry ExpertPh.D., Biomedical Sciences, university of Tennessee at KnoxvilleB.A., Physics and also Mathematics, Hastings College
Dr. Helmenstine stop a Ph.D. In biomedical sciences and is a scientific research writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels.

You are watching: How many hydrogen atoms are in a molecule of water

Have you ever wondered how plenty of atoms are in a autumn of water or how many molecules room in a single droplet? The answer counts on your an interpretation of thevolume that a droplet that water. Water autumn vary considerably in size, so this beginning number defines the calculation. The remainder of the is a an easy chemistry calculation.

Let's usage the volume of a water drop that is used by the medical and scientific community. The welcomed average volume that a drop of water is exactly 0.05 mL (20 drops every milliliter). It transforms out there are over 1.5 sextillion molecule in a drop of water and much more than 5 sextillion atoms per droplet.

chemistry Formula of Water

To calculation the number of molecules and also atoms in a water drop, you require to recognize the chemistry formula that water. There space two atoms of hydrogen and also one atom the oxygen in each water molecule, do the formula H2O. So, each molecule of water has 3 atoms.

Molar massive of Water

Determine the molar massive of water. Carry out this by including up the mass of hydrogen atoms and oxygen atoms in a mole that water through looking up the atomic mass the hydrogen and also oxygen on theperiodic table. The fixed of hydrogen is 1.008 g/mol and also the fixed of oxygen is 16.00 g/mol, for this reason the massive of a mole of water have the right to be calculated as follows:

density of Water

Use the density of water to recognize the massive of water per unit volume. Thedensity of wateractually different depending on conditions (cold water is denser; warmth water is much less dense), but the value typically used in calculations is 1.00 gram per milliliter (1 g/mL). In other words, 1 milliliter of water has a fixed of 1 gram. A drop of water is 0.05 mL the water, therefore its mass would be 0.05 grams.

moles of water in one autumn = 0.05 grams x (1 mole/18.016 grams)moles of water in one fall = 0.002775 moles

making use of Avogrado's Number

Finally, useAvogadro"s number to recognize the variety of molecules in a fall of water. Avogadro"s number tells us there are6.022 x 1023molecules the water per mole of water. So, next we calculation how countless molecules there are in a fall of water, which we determined consists of 0.002775 moles:

molecules in a fall of water = (6.022 x 1023 molecules/mole) x 0.002275 molesmolecules in a autumn of water = 1.67 x 1021 water molecules
atoms in a autumn of water = 3 atoms/molecule x 1.67 x 1021 moleculesatoms in a drop of water = 5.01 x 1021 atoms

atom in a autumn of Water vs. Drops in the ocean

One exciting question is whether over there are much more atoms in a fall of water than there space drops of water in the ocean. To recognize the answer, we need the volume the water in the oceans. Sources estimate this come be in between 1.3 exchange rate km3 and 1.5 km3. I'll use the USGS (United claims Geologic Survey) worth of 1.338 billion km3 for the sample calculation, yet you have the right to use whichever number you would certainly like.

Now, her answer depends on the dimension of your drop, for this reason you division this volume by your drop volume (0.05 ml or 0.00005 together or 5.0 x 10-5 l is the average) to gain the number of drops of water in the ocean.

number of drops of water in the s = 1.338 x 1021 liters full volume / 5.0 x 10-5 liters per drop

So, over there are an ext drops that water in the s than there are atoms in a drop of water. How many much more drops depends greatly on the dimension of her drops, but there space between 1,000 and also 100,000 an ext drops that water in the s than atom in a drop of water.


Gleick, P.H. "Where is Earth"s Water." Earth"s Water Distribution. U.S. Geological Survey, 28August2006.

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Helmenstine, anne Marie, Ph.D. "Calculating the number of Atoms and also Molecules in a fall of Water.", Aug. 25, 2020,, ann Marie, Ph.D. (2020, august 25). Calculating the number of Atoms and Molecules in a autumn of Water. Retrieved indigenous, anne Marie, Ph.D. "Calculating the variety of Atoms and also Molecules in a fall of Water." Https:// (accessed December 22, 2021).