atomic weight

American  

noun

Chemistry.

1. the average weight of an atom of an element, formerly based on the weight of one hydrogen atom taken as a unit or on 1/16 (0.0625) the weight of an oxygen atom, but after 1961 based on 1/12 the weight of the carbon-12 atom. at. wt.

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atomic weight British  

noun

1.  at wt.  the former name for relative atomic mass

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atomic weight Scientific  

1. The mass of an atom expressed in atomic mass units. The atomic weight of an element having more than one principal isotope is calculated both from the atomic masses of the isotopes and from the relative abundance of each isotope in nature. For example, the atomic weight of the element chlorine is 35.453, determined by averaging the atomic masses and relative abundances of its two main naturally occurring isotopes, which have atomic masses of about 35 and 37.

2. Also called relative atomic mass

3. Compare atomic mass See also mass number

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atomic weight Cultural  

1. The mass of a given atom, measured on a scale in which the hydrogen atom has the weight of one. Because most of the mass in an atom is in the nucleus, and each proton and neutron has an atomic weight near one, the atomic weight is very nearly equal to the number of protons and neutrons in the nucleus. (See atomic number.)

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Etymology

Origin of atomic weight

First recorded in 1820–30

Compare meaning

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

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