Not to be confused with the 21 mononuclidic elements, defined as those with only one significant naturally-abundant nuclide.
A monoisotopic element is an element which has only a single stable isotope (nuclide). There are only 26 elements that have this property. A list is given in a following section.
Stability is experimentally defined for chemical elements, as there are a number of stable nuclides with atomic numbers over ~40 which are theoretically unstable, but apparently have half-lives so long that they have not been observed directly or indirectly (from measurement of products) to decay.
Monoisotopic elements are characterized, except in a single case, by odd numbers of protons (odd Z), and even numbers of neutrons. Because of the energy gain from nuclear pairing effects, the odd number of protons imparts instability to isotopes of an odd Z, which in heavier elements requires a completely paired set of neutrons to offset this tendency into stability. (The five stable nuclides with odd Z and odd neutron numbers are hydrogen-2, lithium-6, boron-10, nitrogen-14, and tantalum-180m1.)
The single mononuclidic exception to the odd Z rule is beryllium; its single stable, primordial isotope, beryllium-9, has 4 protons and 5 neutrons. This element is prevented from having a stable isotope with equal numbers of neutrons and protons (beryllium-8, with 4 of each) by its instability toward alpha decay, which is favored due to the extremely tight binding of helium-4 nuclei. It is prevented from having a stable isotope with 4 protons and 6 neutrons by the very large mismatch in proton/neutron ratio for such a light element. (Nevertheless, beryllium-10 has a half-life of 1.36 million years, which is too short to be primordial, but still indicates unusual stability for a light isotope with such an imbalance.)
The set of monoisotopic elements overlap but are not the same as the set of 21 mononuclidic elements, which are characterized as having essentially only one isotope (nuclide) found in nature.[1] The reason for this is the occurrence of certain long-lived radioactive primordial nuclides in nature, which may form admixtures with the monoisotopics, and thus prevent them from being naturally mononuclidic. This happens in the cases of 7 (26 − 19 = 7) of the monoisotopic elements. These isotopes are monoisotopic, but due to the presence of the long-lived radioactive primordial nuclide, are not mononuclidic. These elements are vanadium, rubidium, indium, lanthanum, europium, lutetium and rhenium. See the list below; in two noted cases (indium and rhenium), the long-lived radionuclide is actually the most abundant isotope in nature, and the stable isotope is less abundant.
In 2 additional cases (bismuth[2] and protactinium), mononuclidic elements occur primordially which are not monoisotopic because the naturally occurring nuclide is radioactive, and thus the element has no stable isotopes at all. For an element to be monoisotopic, it must have one stable nuclide.
List of (observationally-stable) monoisotopic elements, ordered by atomic number and weight
Non-mononuclidic elements are marked with an asterisk, and the long-lived primordial radioisotope given. In two notable cases (indium and rhenium), the most abundant naturally occurring isotope is the mildly radioactive one, and in the case of europium, nearly half of it is.
^N. E. Holden, "Standard Atomic Weight Values for the Mononuclidic Elements - 2001," BNL-NCS-68362, Brookhaven National Laboratory (2001)
^Until 2003, 209Bi was thought to be in the first category. It was then found to have a half-life of 1019 years, about a billion times the age of the universe. See Bismuth
External links
Atomic Weights of the Elements as of year 2000, with a section on monoisotopics starting page 708
January 05, 2023
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Not to be confused with the 21 mononuclidic elements defined as those with only one significant naturally abundant nuclide A monoisotopic element is an element which has only a single stable isotope nuclide There are only 26 elements that have this property A list is given in a following section Monoisotopic and mononuclidic elements Monoisotopic but primordial radionuclides exist Stability is experimentally defined for chemical elements as there are a number of stable nuclides with atomic numbers over 40 which are theoretically unstable but apparently have half lives so long that they have not been observed directly or indirectly from measurement of products to decay Monoisotopic elements are characterized except in a single case by odd numbers of protons odd Z and even numbers of neutrons Because of the energy gain from nuclear pairing effects the odd number of protons imparts instability to isotopes of an odd Z which in heavier elements requires a completely paired set of neutrons to offset this tendency into stability The five stable nuclides with odd Z and odd neutron numbers are hydrogen 2 lithium 6 boron 10 nitrogen 14 and tantalum 180m1 The single mononuclidic exception to the odd Z rule is beryllium its single stable primordial isotope beryllium 9 has 4 protons and 5 neutrons This element is prevented from having a stable isotope with equal numbers of neutrons and protons beryllium 8 with 4 of each by its instability toward alpha decay which is favored due to the extremely tight binding of helium 4 nuclei It is prevented from having a stable isotope with 4 protons and 6 neutrons by the very large mismatch in proton neutron ratio for such a light element Nevertheless beryllium 10 has a half life of 1 36 million years which is too short to be primordial but still indicates unusual stability for a light isotope with such an imbalance Contents 1 Differentiation from mononuclidic elements 2 List of observationally stable monoisotopic elements ordered by atomic number and weight 3 See also 4 References 5 External linksDifferentiation from mononuclidic elements EditThe set of monoisotopic elements overlap but are not the same as the set of 21 mononuclidic elements which are characterized as having essentially only one isotope nuclide found in nature 1 The reason for this is the occurrence of certain long lived radioactive primordial nuclides in nature which may form admixtures with the monoisotopics and thus prevent them from being naturally mononuclidic This happens in the cases of 7 26 19 7 of the monoisotopic elements These isotopes are monoisotopic but due to the presence of the long lived radioactive primordial nuclide are not mononuclidic These elements are vanadium rubidium indium lanthanum europium lutetium and rhenium See the list below in two noted cases indium and rhenium the long lived radionuclide is actually the most abundant isotope in nature and the stable isotope is less abundant In 2 additional cases bismuth 2 and protactinium mononuclidic elements occur primordially which are not monoisotopic because the naturally occurring nuclide is radioactive and thus the element has no stable isotopes at all For an element to be monoisotopic it must have one stable nuclide List of observationally stable monoisotopic elements ordered by atomic number and weight EditNon mononuclidic elements are marked with an asterisk and the long lived primordial radioisotope given In two notable cases indium and rhenium the most abundant naturally occurring isotope is the mildly radioactive one and in the case of europium nearly half of it is Beryllium 9 Fluorine 19 Sodium 23 Aluminium 27 Phosphorus 31 Scandium 45 Vanadium 51 naturally occurs with 0 25 of radioactive vanadium 50 Manganese 55 Cobalt 59 Arsenic 75 Rubidium 85 naturally occurs with 27 835 of radioactive rubidium 87 Yttrium 89 Niobium 93 Rhodium 103 Indium 113 naturally occurs with majority 95 7 radioactive isotope indium 115 Iodine 127 Caesium 133 Lanthanum 139 naturally occurs with 0 09 radioactive lanthanum 138 Praseodymium 141 Europium 153 naturally occurs with 47 8 radioactive europium 151 Terbium 159 Holmium 165 Thulium 169 Lutetium 175 naturally occurs with 2 59 radioactive lutetium 176 Rhenium 185 naturally occurs with majority 62 6 radioactive isotope rhenium 187 Gold 197See also EditPrimordial nuclide List of nuclides sorted by half life Table of nuclides Isotope geochemistry Radionuclide Mononuclidic element Stable isotope List of elements by stability of isotopesReferences Edit N E Holden Standard Atomic Weight Values for the Mononuclidic Elements 2001 BNL NCS 68362 Brookhaven National Laboratory 2001 Until 2003 209Bi was thought to be in the first category It was then found to have a half life of 1019 years about a billion times the age of the universe See BismuthExternal links EditAtomic Weights of the Elements as of year 2000 with a section on monoisotopics starting page 708 Retrieved from https en wikipedia org w index php title Monoisotopic element amp oldid 1130696497, wikipedia, wiki, book, books, library,
