atomic number

noun

Definition of atomic number

: 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 Naturally occurring silicon has an atomic number of 14, with 14 electrons that are arranged in valence layers of 2, 8, and 4. Caroline Delbert, Popular Mechanics, "Artificial Atoms Could Usher In the Quantum Revolution," 11 Feb. 2020 Some rare earths are heavy and some are light, depending on their atomic number, and the two have different applications. Naomi Xu Elegant, Fortune, "How 2 American Rare Earth Companies Are Looking Past the Trade War—to Prepare for the Tech War," 10 Sep. 2019 How to Read the Table Many periodic tables include the atomic number (number of protons) and atomic weight (which depends on protons and neutrons). Bill Andrews, Discover Magazine, "Everything Worth Knowing About The Periodic Table," 26 June 2019 For the types of BECs that form droplets, the repulsive forces are not just a function of the density but also the atomic number. Chris Lee, Ars Technica, "Bose Einstein condensate may reveal supersolid’s secrets," 28 Nov. 2018 Among the atoms resulting from neutron bombardment were much smaller atoms like barium, which has an atomic number of 56. Umair Irfan, Vox, "Uranium enrichment will be a key point in talks with North Korea. Here’s what it is.," 11 June 2018 Here are some of the basics: Uranium is the heaviest naturally occurring element in the periodic table, with an atomic number of 92, representing the number of protons in its nucleus. Umair Irfan, Vox, "Uranium enrichment will be a key point in talks with North Korea. Here’s what it is.," 11 June 2018 What metallic element, whose atomic number is 27, was featured on Thursday's show and cited for its use in everything from paints to steel to electric car batteries? CNN, "CNN 10 - May 4, 2018," 3 May 2018 The chemical element with the atomic number 44 is called ruthenium. Mark Inabinett, AL.com, "Watch Hank Aaron hit 715 on 44th anniversary of historic homer," 8 Apr. 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'atomic number.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of atomic number

1913, in the meaning defined above

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Time Traveler for atomic number

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The first known use of atomic number was in 1913

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Last Updated

25 Feb 2020

Cite this Entry

“Atomic number.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/atomic%20number. Accessed 6 Apr. 2020.

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More Definitions for atomic number

atomic number

noun
atomic num·​ber | \ -ˈnəm-bər How to pronounce atomic number (audio) \

Medical Definition of atomic number

: 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

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Britannica.com: Encyclopedia article about atomic number

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