Monoisotopic element
Encyclopedia
A monoisotopic element is one of 26 chemical elements which have only a single stable isotope
(nuclide). 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 ~ 30 which are theorically 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 element, which typically requires at least a completely paired set of neutrons to offset into stability.
The single mononuclidic exception is beryllium, which has 4 protons and 5 neutrons. This isotope is prevented from having equal numbers of neutrons and protons (4 of each) by the instability toward double-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 22 mononuclidic elements, which are characterized as having essentially only one isotope (nuclide) found in nature. The reason for this is the occurrence of certain long-lived radioactive primordial nuclide
s 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 minus 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
, rhenium
and lutetium. See the list below; in two noted cases, the long-lived radionuclide is actually the most abundant isotope in nature, and the stable isotope is less abundant.
In 3 additional cases (bismuth
, thorium
, and protactinium
), mononuclidic elements occur primordially which are not monoisotopic because the naturally-occurring primordial nuclide consists entirely of a single radioisotope (radionuclide), and thus the element has no stable isotopes at all. For an element to be monoisotopic, it must have one stable nuclide.
given. In two notable cases (indium and rhenium), the highest abundance naturally occurring isotope is the mildly radioactive one, and in the case of europium, nearly half of it is.
Stable isotope
Stable isotopes are chemical isotopes that may or may not be radioactive, but if radioactive, have half-lives too long to be measured.Only 90 nuclides from the first 40 elements are energetically stable to any kind of decay save proton decay, in theory...
(nuclide). 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 ~ 30 which are theorically 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 element, which typically requires at least a completely paired set of neutrons to offset into stability.
The single mononuclidic exception is beryllium, which has 4 protons and 5 neutrons. This isotope is prevented from having equal numbers of neutrons and protons (4 of each) by the instability toward double-alpha decay
Alpha decay
Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less...
, 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
Beryllium-10
Beryllium-10 is a radioactive isotope of beryllium. It is formed mainly by cosmic ray spallation. Be-10 has a half-life of 1.36 × 106 years, and decays by beta decay to stable Boron-10 with a maximum energy of 556.2 keV....
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).
Differentiation from similar term
Primordial nuclide
In geochemistry and geonuclear physics, primordial nuclides or primordial isotopes are nuclides found on the earth that have existed in their current form since before Earth was formed. Only 288 such nuclides are known...
s 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 minus 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
Vanadium
Vanadium is a chemical element with the symbol V and atomic number 23. It is a hard, silvery gray, ductile and malleable transition metal. The formation of an oxide layer stabilizes the metal against oxidation. The element is found only in chemically combined form in nature...
, rubidium
Rubidium
Rubidium is a chemical element with the symbol Rb and atomic number 37. Rubidium is a soft, silvery-white metallic element of the alkali metal group. Its atomic mass is 85.4678. Elemental rubidium is highly reactive, with properties similar to those of other elements in group 1, such as very rapid...
, indium
Indium
Indium is a chemical element with the symbol In and atomic number 49. This rare, very soft, malleable and easily fusible post-transition metal is chemically similar to gallium and thallium, and shows the intermediate properties between these two...
, lanthanum
Lanthanum
Lanthanum is a chemical element with the symbol La and atomic number 57.Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is the first element of the lanthanide series. It is found in some rare-earth minerals, usually in combination with cerium and...
, europium
Europium
Europium is a chemical element with the symbol Eu and atomic number 63. It is named after the continent of Europe. It is a moderately hard silvery metal which readily oxidizes in air and water...
, rhenium
Rhenium
Rhenium is a chemical element with the symbol Re and atomic number 75. It is a silvery-white, heavy, third-row transition metal in group 7 of the periodic table. With an average concentration of 1 part per billion , rhenium is one of the rarest elements in the Earth's crust. The free element has...
and lutetium. See the list below; in two noted cases, the long-lived radionuclide is actually the most abundant isotope in nature, and the stable isotope is less abundant.
In 3 additional cases (bismuth
Bismuth
Bismuth is a chemical element with symbol Bi and atomic number 83. Bismuth, a trivalent poor metal, chemically resembles arsenic and antimony. Elemental bismuth may occur naturally uncombined, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead...
, thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....
, and protactinium
Protactinium
Protactinium is a chemical element with the symbol Pa and atomic number 91. It is a dense, silvery-gray metal which readily reacts with oxygen, water vapor and inorganic acids. It forms various chemical compounds where protactinium is usually present in the oxidation state +5, but can also assume...
), mononuclidic elements occur primordially which are not monoisotopic because the naturally-occurring primordial nuclide consists entirely of a single radioisotope (radionuclide), 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 radioisotopePrimordial nuclide
In geochemistry and geonuclear physics, primordial nuclides or primordial isotopes are nuclides found on the earth that have existed in their current form since before Earth was formed. Only 288 such nuclides are known...
given. In two notable cases (indium and rhenium), the highest abundance naturally occurring isotope is the mildly radioactive one, and in the case of europium, nearly half of it is.
See also
- Primordial element
- Primordial nuclidePrimordial nuclideIn geochemistry and geonuclear physics, primordial nuclides or primordial isotopes are nuclides found on the earth that have existed in their current form since before Earth was formed. Only 288 such nuclides are known...
- Table of nuclides sorted by half-life
- Table of nuclidesTable of nuclidesThe tables listed below provide information on the basic properties of all nuclides.* Neutron + Element 1 - Element 24 * Element 25 - Element 48 * Element 49 - Element 72...
- Isotope geochemistryIsotope geochemistryIsotope geochemistry is an aspect of geology based upon study of the relative and absolute concentrations of the elements and their isotopes in the Earth. Variations in the abundance of these isotopes, typically measured with an isotope ratio mass spectrometer or an accelerator mass spectrometer,...
- RadionuclideRadionuclideA radionuclide is an atom with an unstable nucleus, which is a nucleus characterized by excess energy available to be imparted either to a newly created radiation particle within the nucleus or to an atomic electron. The radionuclide, in this process, undergoes radioactive decay, and emits gamma...
- Mononuclidic element
- Stable isotopeStable isotopeStable isotopes are chemical isotopes that may or may not be radioactive, but if radioactive, have half-lives too long to be measured.Only 90 nuclides from the first 40 elements are energetically stable to any kind of decay save proton decay, in theory...
- List of elements by stability of isotopes
- List of elements by nuclear stability