atomic mass

American  

[uh-tom-ik mas] / əˈtɒm ɪk ˈmæs /

noun

Chemistry.

1. the mass of an isotope of an element measured in units formerly based on the mass of one hydrogen atom taken as a unit or on 1/16 (0.0625) the mass of one oxygen atom, but after 1961 based on 1/12 (0.0833) the mass of the carbon-12 atom.

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atomic mass British  

noun

1. the mass of an isotope of an element in atomic mass units

2. short for relative atomic mass See atomic weight

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atomic mass Scientific  

1. The mass of a given atom or molecule, expressed in atomic mass units.

2. Compare atomic weight See also mass number

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Etymology

Origin of atomic mass

First recorded in 1895–1900

Compare meaning

How does atomic-mass compare to similar and commonly confused words? Explore the most common comparisons:

• atomic mass vs. atomic number
• mass number vs. atomic mass
• atomic weight vs. atomic mass

Example Sentences

Broadly speaking, atomic mass is based on the number of protons and neutrons in the nucleus of one atom of that element.

From Science Daily • Dec. 7, 2023

Wallner is particularly interested in the radioactive iron isotope with the atomic mass of 60.

From Science Daily • Nov. 2, 2023

Twelve, named for the atomic mass of carbon, has developed a process to make jet fuel using renewable electricity, water and waste biomass CO2 instead of fossil fuels.

From Seattle Times • Jul. 12, 2023

When a naturally occurring element is composed of several isotopes, the atomic mass of the element represents the average of the masses of the isotopes involved.

From Textbooks • Feb. 14, 2019

The best evidence that these particles are of atomic mass is furnished by their deflection in electric and magnetic fields.

From A Brief Account of Radio-activity by Venable, Francis Preston