List of elements by stability of isotopes


consist of protons and neutrons, which attract each other through the nuclear force, while protons repel each other via the electric force due to their positive charge. These two forces compete, leading to some combinations of neutrons and protons being more stable than others. Neutrons stabilize the nucleus, because they attract protons, which helps offset the electrical repulsion between protons. As a result, as the number of protons increases, an increasing ratio of neutrons to protons is needed to form a stable nucleus; if too many or too few neutrons are present with regard to the optimum ratio, the nucleus becomes unstable and subject to certain types of nuclear decay. Unstable isotopes decay through various radioactive decay pathways, most commonly alpha decay, beta decay, or electron capture. Many rare types of decay, such as spontaneous fission or cluster decay, are known.
half-lives. The darker more stable isotope region departs from the line of protons = neutrons, as the element number Z becomes larger.
Of the first 82 elements in the periodic table, 80 have isotopes considered to be stable. The 83rd element, bismuth, was traditionally regarded as having the heaviest stable isotope, bismuth-209, but in 2003 researchers in Orsay, France, measured the half-life of to be. Technetium and promethium and all the elements with an atomic number over 82 only have isotopes that are known to decompose through radioactive decay. No undiscovered elements are expected to be stable; therefore, lead is considered the heaviest stable element. However, it is possible that some isotopes that are now considered stable will be revealed to decay with extremely long half-lives. This list depicts what is agreed upon by the consensus of the scientific community as of 2019.
For each of the 80 stable elements, the number of the stable isotopes is given. Only 90 isotopes are expected to be perfectly stable, and an additional 162 are energetically unstable, but have never been observed to decay. Thus, 252 isotopes are stable by definition. Those that may in the future be found to be radioactive are expected to have half-lives longer than 1022 years.
In April 2019 it was announced that the half-life of xenon-124 had been measured to 1.8 × 1022 years. This is the longest half-life directly measured for any unstable isotope; only the half-life of tellurium-128 is longer.
Of the chemical elements, only one element has 10 such stable isotopes, five have seven isotopes, eight have six isotopes, ten have five isotopes, nine have four isotopes, five have three stable isotopes, 16 have two stable isotopes, and 26 have a single stable isotope.
Additionally, about 30 nuclides of the naturally occurring elements have unstable isotopes with a half-life larger than the age of the Solar System. An additional four nuclides have half-lives longer than 100 million years, which is far less than the age of the solar system, but long enough for some of them to have survived. These 34 radioactive naturally occurring nuclides comprise the radioactive primordial nuclides. The total number of primordial nuclides is then 252 plus the 34 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.
One of the primordial nuclides is tantalum-180m, which is predicted to have a half-life in excess of 1015 years, but has never been observed to decay. The even-longer half-life of 2.2 × 1024 years of tellurium-128 was measured by a unique method of detecting its radiogenic daughter xenon-128 and is the longest known experimentally measured half-life. Another notable example is the only naturally occurring isotope of bismuth, bismuth-209, which has been predicted to be unstable with a very long half-life, but has been observed to decay. Because of their long half-lives, such isotopes are still found on Earth in various quantities, and together with the stable isotopes they are called primordial isotope. All the primordial isotopes are given in order of their decreasing abundance on Earth.. For a list of primordial nuclides in order of half-life, see List of nuclides.
118 chemical elements are known to exist. All elements to element 94 are found in nature, and the remainder of the discovered elements are artificially produced, with isotopes all known to be highly radioactive with relatively short half-lives. The elements in this list are ordered according to the lifetime of their most stable isotope. Of these, three elements are primordial because they have half-lives long enough to still be found on the Earth, while all the others are produced either by radioactive decay or are synthesized in laboratories and nuclear reactors. Only 13 of the 38 known-but-unstable elements have isotopes with a half-life of at least 100 years. Every known isotope of the remaining 25 elements is highly radioactive; these are used in academic research and sometimes in industry and medicine. Some of the heavier elements in the periodic table may be revealed to have yet-undiscovered isotopes with longer lifetimes than those listed here.
About 338 nuclides are found naturally on Earth. These comprise 252 stable isotopes, and with the addition of the 34 long-lived radioisotopes with half-lives longer than 100 million years, a total of 286 primordial nuclides, as noted above. The nuclides found naturally comprise not only the 286 primordials, but also include about 52 more short-lived isotopes that are daughters of primordial isotopes ; or else are made by energetic natural processes, such as carbon-14 made from atmospheric nitrogen by bombardment from cosmic rays.

Elements by number of primordial isotopes

An even number of protons or neutrons is more stable because of pairing effects, so even–even nuclides are much more stable than odd–odd. One effect is that there are few stable odd–odd nuclides: in fact only five are stable, with another four having half-lives longer than a billion years.
Another effect is to prevent beta decay of many even–even nuclides into another even–even nuclide of the same mass number but lower energy, because decay proceeding one step at a time would have to pass through an odd–odd nuclide of higher energy. This makes for a larger number of stable even–even nuclides, up to three for some mass numbers, and up to seven for some atomic numbers and at least four for all stable even-Z elements beyond iron.
Since a nucleus with an odd number of protons is relatively less stable, odd-numbered elements tend to have fewer stable isotopes. Of the 26 "monoisotopic" elements that have only a single stable isotope, all but one have an odd atomic number—the single exception being beryllium. In addition, no odd-numbered element has more than two stable isotopes, while every even-numbered element with stable isotopes, except for helium, beryllium, and carbon, has at least three.

Tables

The following tables give the elements with primordial nuclides, which means that the element may still be identified on Earth from natural sources, having been present since the Earth was formed out of the solar nebula. Thus, none are shorter-lived daughters of longer-lived parental primordials, such as radon. Two nuclides which have half-lives long enough to be primordial, but have not yet been conclusively observed as such, have been excluded.
The tables of elements are sorted in order of decreasing number of nuclides associated with each element. Stable and unstable nuclides are given, with symbols for unstable nuclides in italics. Note that the sorting does not quite give the elements purely in order of stable nuclides, since some elements have a larger number of long-lived unstable nuclides, which place them ahead of elements with a larger number of stable nuclides. By convention, nuclides are counted as "stable" if they have never been observed to decay by experiment or from observation of decay products.
The first table is for even-atomic numbered elements, which tend to have far more primordial nuclides, due to the stability conferred by proton-proton pairing. A second separate table is given for odd-atomic numbered elements, which tend to have far fewer stable and long-lived unstable nuclides.


Elements with no primordial isotopes


Z
Element
t1⁄2Longest
lived
isotope
94plutonium
96curium
43technetium
93neptunium
91protactinium32,760 a
95americium7,370 a
88radium1,600 a
97berkelium1,380 a
98californium900 a
84polonium125 a
89actinium21.772 a
61promethium17.7 a
99einsteinium1.293 a
100fermium100.5 d
101mendelevium51.3 d
86radon3.823 d
105dubnium1.2 d

Z
Element
t1⁄2Longest
lived
isotope
103lawrencium11 h
85astatine8.1 h
104rutherfordium1.3 h
102nobelium58 min
87francium22 min
106seaborgium14 min
111roentgenium1.7 min
107bohrium1 min
112copernicium28 s
108hassium16 s
110darmstadtium12.7 s
113nihonium9.5 s
109meitnerium4.5 s
114flerovium1.9 s
115moscovium650 ms
116livermorium57 ms
117tennessine51 ms
118oganesson690 μs

Footnotes