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

You are watching: How many hydrogen atoms are in water

Have you ever before wondered how countless atoms room in a fall of water or how plenty of molecules space in a solitary droplet? The answer counts on your definition of thevolume the a droplet of water. Water fall vary substantially in size, so this starting number specifies the calculation. The rest of the is a basic chemistry calculation.

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

chemical Formula the Water

To calculate the variety of molecules and also atoms in a water drop, you require to know the chemical formula of water. There room two atoms of hydrogen and also one atom the oxygen in each water molecule, making the formula H2O. So, each molecule the water has 3 atoms.

Molar mass of Water

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

density of Water

Use the density of water to identify the fixed of water per unit volume. Thedensity the wateractually varies depending on conditions (cold water is denser; heat water is less dense), but the value commonly used in calculations is 1.00 gram every milliliter (1 g/mL). In various other words, 1 milliliter the water has actually a fixed of 1 gram. A fall of water is 0.05 mL of water, so its mass would certainly be 0.05 grams.

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

using Avogrado's Number

Finally, useAvogadro"s number to identify the variety of molecules in a autumn of water. Avogadro"s number tells united state there are6.022 x 1023molecules the water per mole that water. So, next we calculate how plenty of molecules there room in a drop of water, which we determined consists of 0.002775 moles:

molecules in a drop 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 fall of water = 3 atoms/molecule x 1.67 x 1021 moleculesatoms in a autumn of water = 5.01 x 1021 atoms

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

One amazing question is whether there are an ext atoms in a autumn of water than there space drops of water in the ocean. To determine the answer, we need the volume the water in the oceans. Resources estimate this come be in between 1.3 billion km3 and also 1.5 km3. I'll usage the USGS (United says Geologic Survey) value of 1.338 exchange rate km3 for the sample calculation, however you have the right to use whichever number you would like.

Now, her answer relies on the size of your drop, for this reason you divide this volume by your drop volume (0.05 ml or 0.00005 together or 5.0 x 10-5 l is the average) to acquire the number of drops that 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 every drop

So, there are much more drops the water in the ocean than there are atoms in a autumn of water. Just how many more drops depends greatly on the size of your drops, yet there are between 1,000 and 100,000 more drops the water in the ocean than atom in a drop of water.


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

See more: What Lies Before Us And What Lies Behind Meaning, Lies Behind Us

Helmenstine, anne Marie, Ph.D. "Calculating the number of Atoms and also Molecules in a autumn of Water.", Aug. 25, 2020,, ann Marie, Ph.D. (2020, respectable 25). Calculating the number of Atoms and Molecules in a drop of Water. Retrieved native, anne Marie, Ph.D. "Calculating the number of Atoms and Molecules in a drop of Water." Https:// (accessed February 15, 2022).