Atomic weight


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.
Abbreviation: at. wt.
Historical Examples

From the following data calculate the atomic weight of sulphur.
An Elementary Study of Chemistry William McPherson

We see, therefore, that the atomic weight is twice the equivalent, or 55.9.
An Elementary Study of Chemistry William McPherson

Why nail the “power metal” down to an isotope of gold with an atomic weight of 197?
Despoilers of the Golden Empire Gordon Randall Garrett

The atomic weight of manganese has been frequently determined.
Encyclopaedia Britannica, 11th Edition, Volume 17, Slice 5 Various

Thus from uranium with an atomic weight of 238 to radium there is a loss of three alpha particles.
A Brief Account of Radio-activity Francis Preston Venable

These are the signs for the atomic weight of lead, and of silicium.
The Inferno August Strindberg

Its atomic weight has been determined by several careful investigators and is accepted as 226.
A Brief Account of Radio-activity Francis Preston Venable

The other element, to which he gives the name Nebulium, will have an atomic weight of 2·1.
Are the Planets Inhabited? E. Walter Maunder

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

Substance, of any particular kind, absorb Heat in the degree of its atomic weight.
Dynamic Thought William Walker Atkinson

noun
the former name for relative atomic mass at wt

atomic weight n.
Abbr. at wt, AW
The average mass of an atom of an element, usually expressed relative to the atomic mass of carbon 12.
atomic weight
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. Also called relative atomic mass. Compare atomic mass. See also mass number.

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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