mass number

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Related to mass number: Isotopy

mass number,

often represented by the symbol A, the total number of nucleons (neutrons and protons) in the nucleus of an atomatom
[Gr.,=uncuttable (indivisible)], basic unit of matter; more properly, the smallest unit of a chemical element having the properties of that element. Structure of the Atom
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. All atoms of a chemical elementelement,
in chemistry, a substance that cannot be decomposed into simpler substances by chemical means. A substance such as a compound can be decomposed into its constituent elements by means of a chemical reaction, but no further simplification can be achieved.
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 have the same atomic number (number of protons in the nucleus) but may have different mass numbers (from having different numbers of neutrons in the nucleus). Atoms of an element with the same mass number make up an isotopeisotope
, in chemistry and physics, one of two or more atoms having the same atomic number but differing in atomic weight and mass number. The concept of isotope was introduced by F.
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 of the element. Different isotopes of the same element cannot have the same mass number, but isotopes of different elements often do have the same mass number, e.g., carbon-14 (6 protons and 8 neutrons) and nitrogen-14 (7 protons and 7 neutrons).
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Mass number

The mass number A of an atom is the total number of its nuclear constituents, or nucleons, as the protons and neutrons are collectively called. The mass number is placed before and above the elemental symbol, thus 238U. The mass number gives a useful rough figure for the atomic mass; for example, 1H = 1.00814 atomic mass units (amu), 238U = 238.124 amu, and so on. See Atomic number

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.

mass number

Symbol: A. The number of protons and neutrons (i.e. nucleons) in the nucleus of a particular atom. It is the number closest to the mass of a nuclide in atomic mass units, i.e. in units equal to 1/12 of the mass of a carbon-12 atom. See also atomic number.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Mass Number


the number of nucleons (protons and neutrons) in the atomic nucleus; designated by the letter A and usually indicated as a superscript to the left of the symbol of an element. The mass number and charge of a nucleus Z, expressed in units of elementary electric charge, determine the composition of the atomic nucleus: Z protons and (A — Z) neutrons. The mass of any atom, expressed in atomic mass units and rounded to the nearest whole number, is equal to its mass number.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

mass number

[′mas ‚nəm·bər]
(nuclear physics)
The sum of the numbers of protons and neutrons in the nucleus of an atom or nuclide. Also known as nuclear number; nucleon number.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

mass number

the total number of neutrons and protons in the nucleus of a particular atom.
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
It should be mentioned that the first column of the table refers to the constituent elements of the nuclear emulsion, while the second and third column are related to the mass number and root-mean-square (rms) radius of the corresponding elements.
With the exception of 119R X K4S, all crosses involving K4S and N1S had higher scores for gall and egg mass number than the same parent crossed with any other parent.
The "resistance" of a nucleus can be bond by their coupling energy which shows the energy required for destroying the nucleus into its consisting nucleons (their number in the nucleus is equal to the mass number A expressed in atomic units of mass, a.m.u.).
The numbers ([M.sub.A], [M.sub.B], [M.sub.N]), determining the cluster and nucleon structures assumed in each system are taken as follows: [M.sub.A] = 1, [M.sub.N] =2 while [M.sub.B] is different for each reaction and it is equal to B/2, where B is the mass number of the target nucleus.
114, with mass number 289, while scientists suspect nucleus No.
The people claiming they want colorblind admissions aren't likely to welcome mass numbers of Asian American classmates with open arms."
Residents of the community pulled in mass numbers at the church compound to witness the drama, standing in total surprise as church members divided in two groups between the prophet and the senior pastor used alleged abusive languages that this paper cannot mention.
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Beginning next year, you can be confident your new pet didn't come from a puppy mill--a facility where dogs and other animals are bred in mass numbers, often in inhumane conditions.
If sabi ng NPA that they are recruiting in mass numbers and they create trouble, and they are armed and about to destroy government,' he added.
"It is up to the enemies of the state if the NPA say they are creating in mass numbers, they create trouble and they are armed and about to destroy its government," he said, referring to the New People's Army.