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Sorting here sorts by mass number. Z, N column The number of protons (Z column) and number of neutrons (N column). energy column The column labeled "energy" denotes the energy equivalent of the mass of a neutron minus the mass per nucleon of this nuclide (so all nuclides get a positive value) in MeV, formally: m n − m nuclide / A, where A = Z ...
Isotones are nuclides with the same number of neutrons but differing numbers of protons. Isotones neighbor each other horizontally. Examples include carbon-14, nitrogen-15, and oxygen-16 in the table above. Isobars are nuclides with the same number of nucleons (i.e. mass number) but different numbers of protons and neutrons. Isobars neighbor ...
Likewise, nuclides with the same neutron excess (N − Z) are called isodiaphers. [4] The name isotone was derived from the name isotope to emphasize that in the first group of nuclides it is the number of neutrons (n) that is constant, whereas in the second the number of protons (p). [5]
These 35 radioactive naturally occurring nuclides comprise the radioactive primordial nuclides. The total number of primordial nuclides is then 251 (the stable nuclides) plus the 35 radioactive primordial nuclides, for a total of 286 primordial nuclides. This number is subject to change if new shorter-lived primordials are identified on Earth.
In theory, no two stable nuclides have the same mass number (since no two nuclides that have the same mass number are both stable to beta decay and double beta decay), and no stable nuclides exist for mass numbers 5, 8, 143–155, 160–162, and ≥ 165, since in theory, the beta-decay stable nuclides for these mass numbers can undergo alpha decay.
These nuclides lie at the very bottom of the valley of stability. From this bottom, the average binding energy per nucleon slowly decreases with increasing atomic mass number. The heavy nuclide 238 U is not stable, but is slow to decay with a half-life of 4.5 billion years. [1] It has relatively small binding energy per nucleon.
For other isotopes, the isotopic mass is usually within 0.1 u of the mass number. For example, 35 Cl (17 protons and 18 neutrons) has a mass number of 35 and an isotopic mass of 34.96885. [7] The difference of the actual isotopic mass minus the mass number of an atom is known as the mass excess, [8] which for 35 Cl is –0.03115.
Each type of nucleus is called a "nuclide", and each nuclide is defined by the specific number of each type of nucleon. "Isotopes" are nuclides which have the same number of protons but differing numbers of neutrons. Conversely, "isotones" are nuclides which have the same number of neutrons but differing numbers of protons.