atomic number

noun

|Updated on: 17 Jun 2018

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

See atomic number defined for kids

Recent Examples of atomic number from the Web

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
The element, atomic number 16, only accounts for about 0.0007 percent of all matter.

— jay bennett, Popular Mechanics, "To Find Life in Our Galaxy, Follow the Phosphorus," 4 Apr. 2018
These rods were inserted into a nuclear reactor and bombarded with neutrons, tiny, uncharged subatomic particles, with the hope that some would get stuck to uranium atoms, increasing their atomic number to 239.

— julian g. west, The Atlantic, "The Atomic-Bomb Core That Escaped World War II," 2 Apr. 2018
Given that titanium features an atomic number of 22 and platinum’s is 78, there seem to be a number of opportunities to plunder the periodic table.

— davey g. johnson, Car and Driver, "More Titanium Than Titanium: Ford Announces 2019 Edge Titanium Elite," 5 Feb. 2018
This picture shows some of these elements, along with their atomic numbers.

— ashley strickland, CNN, "First-seen neutron star collision creates light, gravitational waves and gold," 16 Oct. 2017

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.