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

Because 79 is the atomic number of the chemical element of gold. —Devorah Lev-Tov, Architectural Digest, 17 Oct. 2024

Lead, explained Lead — atomic number 82 on the periodic table — is soft, plentiful, and easy to mine and manipulate, which is why humans have been harnessing it for various purposes for thousands of years. —Dylan Matthews, Vox, 7 Dec. 2018

The periodic table arranges elements based on their atomic number, or the number of protons each element has in its nucleus. —Michael Irving, New Atlas, 25 July 2024

The elements heavier than iron (atomic number 26) form in nature through a process called rapid neutron capture, which often occurs in cataclysmic events such as a collision of two neutron stars. —Stephanie Pappas, Scientific American, 14 May 2024

Word History

First Known Use

1913, in the meaning defined above

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