atomic weight

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.

atomic weight

noun

1. the former name for relative atomic mass at wt

atomic weight

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 massSee also mass number

atomic weight

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 .)

Word History and Origins

Origin of atomic weight¹

First recorded in 1820–30

Example Sentences

She had an atomic weight upon which you could depend as upon any other known quantity.

From Project Gutenberg

The numbers denote the atomic weight of the atom, which is the total number of protons and neutrons in its nucleus.

From Project Gutenberg

Similarly 56 is the atomic weight of iron, and 32 the atomic weight of sulphur.

From Project Gutenberg

Its atomic weight would be about 68; that of gallium is 699.

From Project Gutenberg

The atomic weight of any particular element is the weight of its atom compared with the weight of an atom of hydrogen.

From Project Gutenberg