A nuclide (from nucleus) is an atomic species characterized by the specific constitution of its nucleus, i.e., by its number of protons Z, its number of neutrons N, and its energy state. Thus, all nuclides are atoms that have at least one electron (though certain ions may be included), but naked nuclei (such as those occurring in cosmic rays and sufficiently hot plasmas) do not, in the technical sense, qualify for the term (these are instead naked nuclei of various nuclear species (elements)). In short, a nuclide is a general term for all nuclei with one or more electrons orbiting.
The word nuclide was proposed  by Truman P. Kohman in 1947. Doctor Kohman originally suggested nuclide as referring to a "species of nucleus" defined by containing a certain number of neutrons and protons. The word thus was originally intended to focus on the nucleus.
Nuclides and isotopes
Designation Characteristics Example Remarks Isotopes equal proton number 12
Isotones equal neutron number 13
Isobars equal mass number 17
see beta decay Mirror nuclei neutron and proton number exchanged 3
Nuclear isomers different energy states 99
long-lived or stable
A set of nuclides with equal proton number (atomic number), i.e., of the same chemical element but different neutron numbers, are called isotopes of the element. Particular nuclides are still often loosely called "isotopes", but the term "nuclide" is the correct one in general (i.e., when Z is not fixed). In similar manner, a set of nuclides with equal mass number A but different atomic number are called isobars (isobar = equal in weight), and isotones are nuclides of equal neutron number but different proton numbers. The name isotone has been 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).
See the introduction to the article about isotopes for an explanation of the notation used for different nuclide or isotope types.
Nuclear isomers are members of a set of nuclides with equal proton number and equal mass number, but different states of excitation. An example is the two states of 99
43Tc shown among the decay schemes. The most long-lived non-ground state nuclear isomer is tantalum-180m(180m
73Ta), which has a half-life in excess of 1,000 trillion years, and has not been observed to decay to tantalum-180.
There are about 255 nuclides in nature that have never been observed to decay. They occur among the 80 different elements that have one or more stable isotopes. See stable isotope and primordial nuclide. Unstable nuclides are radioactive and are called radionuclides. Their decay products ('daughter' products) are called radiogenic nuclides. About 255 stable and about 84 unstable (radioactive) nuclides exist naturally on Earth, for a total of about 339 naturally occurring nuclides on Earth.
Types of naturally occurring nuclides
Natural radionuclides may be conveniently subdivided into three types. First, those whose half-lives T1/2 are at least 2% as long as the age of the earth (for practical purposes, these are difficult to detect with half-lives less than 10% of the age of the Earth) (4.6×109 yr). These are remnants of nucleosynthesis that occurred in stars before the formation of the solar system. For example, the isotope 238
U (T1/2 = 4.5×109 yr) of uranium is still fairly abundant in nature, but the shorter-lived isotope 235
U (T1/2 = 0.7×109 yr) is 138 times rarer. About 33 of these nuclides have been discovered (see list of nuclides and primordial nuclide for details).
The second group of radionuclides that exist naturally consists of radiogenic nuclides such as 226
Ra (T1/2 = 1,602 yr), an isotope of radium, which are formed by radioactive decay. They occur in the decay chains of primordial isotopes of uranium or thorium. Some of these nuclides are very short-lived, such as isotopes of francium. There exist about 51 of these daughter nuclides that have half-lives too short to be primordial, and which exist in nature solely due to decay from longer lived radioactive primordial nuclides.
The third group consists of nuclides that are continuously being made in another fashion that is not simple spontaneous radioactive decay (i.e., only one atom involved with no incoming particle) but instead involves a natural nuclear reaction. These occur when atoms react with natural neutrons (from cosmic rays, spontaneous fission, or other sources), or are bombarded directly with cosmic rays. The latter, if non-primordial, are called cosmogenic nuclides. Other types of natural nuclear reactions produce nuclides that are said to be nucleogenic nuclides.
An example of nuclides made by nuclear reactions, are cosmogenic 14
C (radiocarbon) that is made by cosmic-ray bombardment of other elements, and nucleogenic 239
Pu which is still being created by neutron bombardment of natural 238
U as a result of natural fission in uranium ores. Cosmogenic nuclides may be either stable or radioactive. If they are stable, their existence must be deduced against a background of stable nuclides, since every known stable nuclide is present on Earth primordially.
Artificially produced nuclides
Beyond the 339 naturally-occurring nuclides, more than 3000 radionuclides of varying half-lives have been artificially produced and characterized.
The known nuclides are shown in the chart of nuclides. A list of primordial nuclides is given sorted by element, at list of elements by stability of isotopes. A list of nuclides is also available, sorted by half-life, for the 905 nuclides with half-lives longer than one hour.
Summary table for numbers of each class of nuclides
This is a summary table  for the 905 nuclides with half-lives longer than one hour, given in list of nuclides. Note that numbers are not exact, and may change slightly in the future, if some "stable" nuclides are observed to be radioactive with very long half-lives.
Stability class Number of nuclides Running total Notes on running total Theoretically stable to all but proton decay 90 90 Includes first 40 elements. Proton decay yet to be observed. Energetically unstable to one or more known decay modes, but no decay yet seen. Spontaneous fission possible for "stable" nuclides > niobium-93; other mechanisms possible for heavier nuclides. All considered "stable" until decay detected. 165 255 Total of classically stable nuclides. Radioactive primordial nuclides. 33 288 Total primordial elements include bismuth, uranium, thorium, plutonium, plus all stable nuclides. Radioactive non-primordial, but naturally occurring on Earth. ~ 51 ~ 339 Carbon-14 (and other cosmogenic isotopes generated by cosmic rays); daughters of radioactive primordials, such as francium, etc., and nucleogenic nuclides from natural nuclear reactions that are other than those from cosmic rays (such as neutron absorption from spontaneous nuclear fission or neutron emission). Radioactive synthetic (half-life > 1 hour). Includes most useful radiotracers. 556 905 Radioactive synthetic (half-life < 1 hour). >2400 >3300 Includes all well-characterized synthetic nuclides.
- Primordial element
- Primordial nuclide
- List of nuclides sorted by half-life
- Table of nuclides
- Isotope geochemistry
- Monoisotopic element
- Mononuclidic element
- Stable isotope
- List of elements by stability of isotopes
- List of elements by nuclear stability
- Exotic nuclei
- ^ IUPAC (1997). "Nuclide". In A. D. McNaught and A. Wilkinson. Compendium of Chemical Terminology. Blackwell Scientific Publications. doi:10.1351/goldbook.N04257. ISBN 0632017651. http://goldbook.iupac.org/N04257.html.
- ^ original proposal for the word nuclide
- ^  about Kohman]
- ^ E.R. Cohen, P. Giacomo (1987). "Symbols, units, nomenclature and fundamental constants in physics". Physica A 146: 1–68. Bibcode 1987PhyA..146....1.. doi:10.1016/0378-4371(87)90216-0.
- ^ Table data is derived by counting members of the list; see WP:CALC. References for the list data itself are given below in the reference section in list of nuclides
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