atomic number
noun
: an experimentally determined number characteristic of a chemical element that represents the number of protons in the nucleus which in a neutral atom equals the number of electrons outside the nucleus and that determines the place of the element in the periodic table see Chemical Elements Table
Examples of atomic number in a Sentence
Recent Examples on the Web
Katie Hafner: Uranium is the last of the naturally occurring elements on the periodic table, with an atomic number of 92.
—
Ashraya Gupta, Scientific American, 7 Sep. 2023
Each box and square with the atomic number just reminded me of another window with some family back there.
—James Sullivan, BostonGlobe.com, 8 June 2023
Though no one is sure how many elements exist, atomic number 119 will be the first in a new row — a new period — that could extend all the way to 172.
—Cody Cottier, Discover Magazine, 12 Apr. 2022
What’s the atomic number of Rolex?
—Charles Curkin, ELLE Decor, 6 Apr. 2023
Many periodic tables include the atomic number (number of protons) and atomic weight (which depends on protons and neutrons).
—Bill Andrews, Discover Magazine, 26 June 2019
Even the rarest rare earth, thulium, with atomic number 69, is 125 times more common than gold.
—Stanley Merzman, Discover Magazine, 21 Aug. 2018
Adding another, to make cerium, atomic number 58, adds an electron to the fourth circle.
—Stanley Merzman, Discover Magazine, 21 Aug. 2018
Along with the name and atomic number of each element, Enevoldsen added helpful graphics and a short explanation of how each element is put to use.
—Nathaniel Scharping, Discover Magazine, 7 Nov. 2016
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Ashraya Gupta, Scientific American, 7 Sep. 2023
Each box and square with the atomic number just reminded me of another window with some family back there.
—James Sullivan, BostonGlobe.com, 8 June 2023
Though no one is sure how many elements exist, atomic number 119 will be the first in a new row — a new period — that could extend all the way to 172.
—Cody Cottier, Discover Magazine, 12 Apr. 2022
What’s the atomic number of Rolex?
—Charles Curkin, ELLE Decor, 6 Apr. 2023
Many periodic tables include the atomic number (number of protons) and atomic weight (which depends on protons and neutrons).
—Bill Andrews, Discover Magazine, 26 June 2019
Even the rarest rare earth, thulium, with atomic number 69, is 125 times more common than gold.
—Stanley Merzman, Discover Magazine, 21 Aug. 2018
Adding another, to make cerium, atomic number 58, adds an electron to the fourth circle.
—Stanley Merzman, Discover Magazine, 21 Aug. 2018
Along with the name and atomic number of each element, Enevoldsen added helpful graphics and a short explanation of how each element is put to use.
—Nathaniel Scharping, Discover Magazine, 7 Nov. 2016
See More
These examples are programmatically compiled from various online sources to illustrate current usage of the word 'atomic number.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.
Word History
First Known Use
1913, in the meaning defined above
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Cite this Entry
“Atomic number.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/atomic%20number. Accessed 24 Sep. 2023.
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Kids Definition
atomic number
noun
: a number that is characteristic of a chemical element and represents the number of protons in the nucleus
Medical Definition
atomic number
noun
atomic num·ber
-ˈnəm-bər 
: an experimentally determined number characteristic of a chemical element that represents the number of protons in the nucleus which in a neutral atom equals the number of electrons outside the nucleus and that determines the place of the element in the periodic table see Chemical Elements Table
More from Merriam-Webster on atomic number
Britannica.com: Encyclopedia article about atomic number
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