# mass number

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Related to mass numbers: Isotopes, atomic number 100, Atomic numbers

## 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
. 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.
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.
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).

## 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

## 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.

## 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.

## 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.

## mass number

the total number of neutrons and protons in the nucleus of a particular atom.
References in periodicals archive ?
That is the balance of energy must be from which the neutrons number N and further the mass number A = N + z can be determined:
where M(Z, A) is the mass of nucleus with Z and A as proton number and mass number, respectively.
Isotope: Any of the several different forms of a chemical element that differ in their atomic mass (mass number); isotopes of an element possess the same number of protons in their nuclei but different numbers of neutrons and therefore differ in their mass numbers, which reflect the total number of protons plus neutrons.
Forgo mass numbers of customers for mass appeal among a smaller, select group.
The 83 year old Nazi guard was part of a program at the infamous Trawniki slave labor camp in Poland during World War II, where Poles like him were trained to exterminate mass numbers of Jews by operating gas chambers.
"The White House Project is dedicated to getting women in leadership positions in every sector of political society and we need to have mass numbers of women running for office to make a dent in the lack of women that hold public office, " Wilson said.
"If you're going to impact things, you've got to do it in mass numbers, and that means designing a car that the most number of people will accept."
In the wake of 9/11, and more recently, Hurricane Katrina, the federal government has made it a top national-security priority to ensure the country's healthcare system has the capacity to provide medical care to mass numbers of sick or injured Americans in the aftermath of a major regional or national catastrophe.
Since objective test items only, are used in standardized tests, machine scoring is possible of mass numbers of tests.
Each of these individual populations had undergone two cycles of selection for low gall and egg mass numbers in response to its specific nematodes before intercrossing selected individuals as one population.
Where M is the higher mass number of the two peaks and [DELTA] M is the difference between the two mass numbers.
But with 150,000 people dying every year from global warming, Greenpeace feels we're in a climate crisis - and if humanity is to solve the problem we need radical action, the kind of action that can only be forced through by mass numbers of people taking action to display the strength of feeling out there.

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