mass number

mass number

noun Physics.
the integer nearest in value to the atomic weight of an atom and equal to the number of nucleons in the nucleus of the atom. Symbol: A

Origin:
1920–25

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Collins
World English Dictionary
mass number
 
n
A, Also called: nucleon number the total number of neutrons and protons in the nucleus of a particular atom

Collins English Dictionary - Complete & Unabridged 10th Edition
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American Heritage
Science Dictionary
mass number  
The total number of protons and neutrons in the nucleus of an atom. For example, nitrogen has 7 protons and 7 neutrons in its nucleus, giving it a mass number of 14. Isotopes of elements are distinguished by their mass number; for example, carbon-12 and carbon-14 have mass numbers of 12 and 14 respectively. Also called nucleon number. Compare atomic mass, atomic weight.

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Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia Britannica
Encyclopedia

mass number

in nuclear physics, the sum of the numbers of protons and neutrons present in the nucleus of an atom. The mass number is commonly cited in distinguishing among the isotopes of an element, all of which have the same atomic number (number of protons) and are represented by the same literal symbol; for example, the two best known isotopes of uranium (those with mass numbers 235 and 238) are designated uranium-235 (symbolized 235U) and uranium-238 (238U).

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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