Chemisattempt ExpertPh.D., Bioclinical Sciences, University of Tennesview at KnoxvilleB.A., Physics and also Mathematics, Hastings College
Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a scientific research writer, educator, and consultant. She has actually taught science courses at the high institution, college, and also graduate levels.

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


Have you ever before wondered exactly how many kind of atoms are in a drop of water or how many kind of molecules are in a solitary droplet? The answer relies on your definition of thevolume of a droplet of water. Water drops differ dramatically in size, so this starting number specifies the calculation. The rest of it is an easy chemisattempt calculation.


Let's usage the volume of a water drop that is supplied by the clinical and also scientific area. The accepted average volume of a drop of water is exactly 0.05 mL (20 drops per milliliter). It transforms out tright here are over 1.5 sextillion molecules in a drop of water and more than 5 sextillion atoms per droplet.


Chemical Formula of Water

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


Molar Mass of Water

Determine the molar mass of water. Do this by adding up the mass of hydrogen atoms and oxygen atoms in a mole of water by looking up the atomic mass of hydrogen and also oxygen on theroutine table. The mass of hydrogen is 1.008 g/mol and the mass of oxygen is 16.00 g/mol, so the mass of a mole of water have the right to be calculated as follows:


Density of Water

Use the density of water to identify the mass of water per unit volume. Thethickness of wateractually varies depending upon conditions (cold water is denser; heat water is less dense), however the worth frequently provided in calculations is 1.00 gram per milliliter (1 g/mL). In various other words, 1 milliliter of water has actually a mass of 1 gram. A drop of water is 0.05 mL of water, so its mass would be 0.05 grams.


moles of water in one drop = 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 recognize the number of molecules in a drop of water. Avogadro"s number tells us there are6.022 x 1023molecules of water per mole of water. So, next we calculate exactly how many molecules tbelow are in a drop of water, which we established includes 0.002775 moles:


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

Atoms in a Drop of Water vs. Drops in the Ocean

One amazing question is whether tbelow are more atoms in a drop of water than there are drops of water in the sea. To recognize the answer, we need the volume of water in the seas. Sources estimate this to be in between 1.3 billion km3 and 1.5 km3. I'll use the USGS (United States Geologic Survey) worth of 1.338 billion km3 for the sample calculation, yet you can usage whichever number you would certainly prefer.


Now, your answer relies on the dimension of your drop, so you divide this volume by your drop volume (0.05 ml or 0.00005 L or 5.0 x 10-5 L is the average) to acquire the number of drops of water in the ocean.


variety of drops of water in the sea = 1.338 x 1021 liters total volume / 5.0 x 10-5 liters per drop


So, there are more drops of water in the sea than there are atoms in a drop of water. How many kind of even more drops relies largely on the size of your drops, however tbelow are between 1,000 and also 100,000 more drops of water in the sea than atoms in a drop of water.


Source

Gleick, P.H. "Wbelow is Earth"s Water." Earth"s Water Distribution. UNITED STATE Geological Survey, 28August2006.

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Helmenstine, Anne Marie, Ph.D. "Calculating the Number of Atoms and also Molecules in a Drop of Water." nlinux.org, Aug. 25, 2020, nlinux.org/atoms-in-a-drop-of-water-609425.Helmenstine, Anne Marie, Ph.D. (2020, August 25). Calculating the Number of Atoms and Molecules in a Drop of Water. Retrieved from https://www.nlinux.org/atoms-in-a-drop-of-water-609425Helmenstine, Anne Marie, Ph.D. "Calculating the Number of Atoms and also Molecules in a Drop of Water." nlinux.org. https://www.nlinux.org/atoms-in-a-drop-of-water-609425 (accessed March 29, 2022).