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atomic weight

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noun Chemistry.

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.

Origin of atomic weight

First recorded in 1820–30
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
British Dictionary definitions for atomic weight

atomic weight

noun

the former name for relative atomic mass Abbreviation: at wt
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
atomic weight in Medicine

atomic weight

n.

The average mass of an atom of an element, usually expressed relative to the atomic mass of carbon 12.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
atomic weight in Science

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 American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
atomic weight in Culture

atomic weight

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.)

The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.