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The mass number (symbol A, from the German word: Atomgewicht, "atomic weight"), [ 1] also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus. It is approximately equal to the atomic (also known as isotopic) mass of the atom expressed in atomic mass units.
The atomic number or nuclear charge number (symbol Z) of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei composed of protons and neutrons, this is equal to the proton number ( np) or the number of protons found in the nucleus of every atom of that element. The atomic number can be used to uniquely identify ...
The neutron number (symbol N) is the number of neutrons in a nuclide . Atomic number (proton number) plus neutron number equals mass number: Z + N = A. The difference between the neutron number and the atomic number is known as the neutron excess: D = N − Z = A − 2Z . Neutron number is not written explicitly in nuclide symbol notation, but ...
An atomic nucleus is formed by a number of protons, Z (the atomic number), and a number of neutrons, N (the neutron number), bound together by the nuclear force. Protons and neutrons each have a mass of approximately one dalton. The atomic number determines the chemical properties of the atom, and the neutron number determines the isotope or ...
Since free protons and neutrons differ from each other in mass by a small fraction of a dalton (1.388 449 33 (49) × 10 −3 Da), [9] rounding the relative isotopic mass, or the atomic mass of any given nuclide given in daltons to the nearest whole number, always gives the nucleon count, or mass number.
where A = Atomic mass number (the number of protons Z, plus the number of neutrons N) and r 0 = 1.25 fm = 1.25 × 10 −15 m. In this equation, the "constant" r 0 varies by 0.2 fm, depending on the nucleus in question, but this is less than 20% change from a constant. [20]
The number of nucleons (both protons and neutrons) in the nucleus is the atom's mass number, and each isotope of a given element has a different mass number. For example, carbon-12, carbon-13, and carbon-14 are three isotopes of the element carbon with mass numbers 12, 13, and 14, respectively. The atomic number of carbon is 6, which means that ...
The atomic binding energy is simply the amount of energy (and mass) released, when a collection of free nucleons are joined to form a nucleus . Nuclear binding energy can be computed from the difference in mass of a nucleus, and the sum of the masses of the number of free neutrons and protons that make up the nucleus.