Chemistry:List of elements by stability of isotopes

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Isotope half-lives. The darker more stable isotope region departs from the line of protons (Z) = neutrons (N), as the element number Z becomes larger.

This is a list of chemical elements by the stability of their isotopes. Of the first 82 elements in the periodic table, 80 have isotopes considered to be stable.[1] Overall, there are 251 known stable isotopes in total.


Atomic nuclei 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. (See Radioactive decay for details.)[citation needed]

Of the first 82 elements in the periodic table, 80 have isotopes considered to be stable.[1] 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 209Bi to be 1.9×1019 years.[2][3] Technetium and promethium (atomic numbers 43 and 61, respectively[lower-alpha 1]) 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 (as with 209Bi). This list depicts what is agreed upon by the consensus of the scientific community as of 2023.[1]

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 161 are energetically unstable,[citation needed] but have never been observed to decay. Thus, 251 isotopes (nuclides) are stable by definition (including tantalum-180m, for which no decay has yet been observed). Those that may in the future be found to be radioactive are expected to have half-lives longer than 1022 years (for example, xenon-134).[citation needed]

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;[4] only the half-life of tellurium-128 is longer.[citation needed]

Of the chemical elements, only 1 element (tin) has 10 such stable isotopes, 5 have 7 stable isotopes, 7 have 6 stable isotopes, 11 have 5 stable isotopes, 9 have 4 stable isotopes, 5 have 3 stable isotopes, 16 have 2 stable isotopes, and 26 have 1 stable isotope.[1]

Additionally, about 31 nuclides of the naturally occurring elements have unstable isotopes with a half-life larger than the age of the Solar System (~109 years or more).[lower-alpha 2] 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 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.[citation needed]

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.[5] 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.[lower-alpha 3] For a list of primordial nuclides in order of half-life, see List of nuclides.[citation needed]

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 (see below). The elements in this list are ordered according to the lifetime of their most stable isotope.[1] Of these, three elements (bismuth, thorium, and uranium) are primordial because they have half-lives long enough to still be found on the Earth,[lower-alpha 4] 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.[lower-alpha 5] Some of the heavier elements in the periodic table may be revealed to have yet-undiscovered isotopes with longer lifetimes than those listed here.[lower-alpha 6]

About 338 nuclides are found naturally on Earth. These comprise 251 stable isotopes, and with the addition of the 35 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 (defined by a half-life less than 100 million years, too short to have survived from the formation of the Earth) that are daughters of primordial isotopes (such as radium from uranium); or else are made by energetic natural processes, such as carbon-14 made from atmospheric nitrogen by bombardment from cosmic rays.[citation needed]

Elements by number of primordial isotopes

An even number of protons or neutrons is more stable (higher binding energy) 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.[citation needed]

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. (Double beta decay directly from even–even to even–even, skipping over an odd-odd nuclide, is only occasionally possible, and is a process so strongly hindered that it has a half-life greater than a billion times the age of the universe.) 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 (proton) numbers and at least four for all stable even-Z elements beyond iron (except strontium and lead).[citation needed]

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. Only a single odd-numbered element, potassium, has three primordial isotopes; none have more than three.[citation needed]


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. Two nuclides which have half-lives long enough to be primordial, but have not yet been conclusively observed as such (244Pu and 146Sm), have been excluded.[citation needed]

The tables of elements are sorted in order of decreasing number of nuclides associated with each element. (For a list sorted entirely in terms of half-lives of nuclides, with mixing of elements, see List of nuclides.) Stable and unstable (marked decays) nuclides are given, with symbols for unstable (radioactive) 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 (extremely long-lived nuclides unstable only in theory, such as tantalum-180m, are counted as stable).[citation needed]

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 (primordial) unstable nuclides.[citation needed]

Primordial isotopes (in order of decreasing abundance on Earth[lower-alpha 3]) of even-Z elements
[lower-alpha 2][1]
unstable in italics[lower-alpha 2]
odd neutron number in pink
50 tin 10 120Sn 118Sn 116Sn 119Sn 117Sn 124Sn 122Sn 112Sn 114Sn 115Sn
54 xenon 7 2 132Xe 129Xe 131Xe 134Xe 136Xe 130Xe 128Xe 124Xe 126Xe
48 cadmium 6 2 114Cd 112Cd 111Cd 110Cd 113Cd 116Cd 106Cd 108Cd
52 tellurium 6 2 130Te 128Te 126Te 125Te 124Te 122Te 123Te 120Te
44 ruthenium 7 102Ru 104Ru 101Ru 99Ru 100Ru 96Ru 98Ru
66 dysprosium 7 164Dy 162Dy 163Dy 161Dy 160Dy 158Dy 156Dy
70 ytterbium 7 174Yb 172Yb 173Yb 171Yb 176Yb 170Yb 168Yb
80 mercury 7 202Hg 200Hg 199Hg 201Hg 198Hg 204Hg 196Hg
42 molybdenum 6 1 98Mo 96Mo 95Mo 92Mo 100Mo 97Mo 94Mo
56 barium 6 1 138Ba 137Ba 136Ba 135Ba 134Ba 132Ba 130Ba
64 gadolinium 6 1 158Gd 160Gd 156Gd 157Gd 155Gd 154Gd 152Gd
60 neodymium 5 2 142Nd 144Nd 146Nd 143Nd 145Nd 148Nd 150Nd
62 samarium 5 2 152Sm 154Sm 147Sm 149Sm 148Sm 150Sm 144Sm
76 osmium 5 2 192Os 190Os 189Os 188Os 187Os 186Os 184Os
46 palladium 6 106Pd 108Pd 105Pd 110Pd 104Pd 102Pd
68 erbium 6 166Er 168Er 167Er 170Er 164Er 162Er
20 calcium 5 1 40Ca 44Ca 42Ca 48Ca 43Ca 46Ca
34 selenium 5 1 80Se 78Se 76Se 82Se 77Se 74Se
36 krypton 5 1 84Kr 86Kr 82Kr 83Kr 80Kr 78Kr
72 hafnium 5 1 180Hf 178Hf 177Hf 179Hf 176Hf 174Hf
78 platinum 5 1 195Pt 194Pt 196Pt 198Pt 192Pt 190Pt
22 titanium 5 48Ti 46Ti 47Ti 49Ti 50Ti
28 nickel 5 58Ni 60Ni 62Ni 61Ni 64Ni
30 zinc 5 64Zn 66Zn 68Zn 67Zn 70Zn
32 germanium 4 1 74Ge 72Ge 70Ge 73Ge 76Ge
40 zirconium 4 1 90Zr 94Zr 92Zr 91Zr 96Zr
74 tungsten 4 1 184W 186W 182W 183W 180W
16 sulfur 4 32S 34S 33S 36S
24 chromium 4 52Cr 53Cr 50Cr 54Cr
26 iron 4 56Fe 54Fe 57Fe 58Fe
38 strontium 4 88Sr 86Sr 87Sr 84Sr
58 cerium 4 140Ce 142Ce 138Ce 136Ce
82 lead 4 208Pb 206Pb 207Pb 204Pb
8 oxygen 3 16O 18O 17O
10 neon 3 20Ne 22Ne 21Ne
12 magnesium 3 24Mg 26Mg 25Mg
14 silicon 3 28Si 29Si 30Si
18 argon 3 40Ar 36Ar 38Ar
2 helium 2 4He 3He
6 carbon 2 12C 13C
92 uranium 0 2 238U[lower-alpha 4] 235U
4 beryllium 1 9Be
90 thorium 0 1 232Th[lower-alpha 4]
Primordial isotopes of odd-Z elements
unstable: italics
odd N in pink
19 potassium 2 1 39K 41K 40K
1 hydrogen 2 1H 2H
3 lithium 2 7Li 6Li
5 boron 2 11B 10B
7 nitrogen 2 14N 15N
17 chlorine 2 35Cl 37Cl
29 copper 2 63Cu 65Cu
31 gallium 2 69Ga 71Ga
35 bromine 2 79Br 81Br
47 silver 2 107Ag 109Ag
51 antimony 2 121Sb 123Sb
73 tantalum 2 181Ta 180mTa
77 iridium 2 193Ir 191Ir
81 thallium 2 205Tl 203Tl
23 vanadium 1 1 51V 50V
37 rubidium 1 1 85Rb 87Rb
49 indium 1 1 115In 113In
57 lanthanum 1 1 139La 138La
63 europium 1 1 153Eu 151Eu
71 lutetium 1 1 175Lu 176Lu
75 rhenium 1 1 187Re 185Re
9 fluorine 1 19F
11 sodium 1 23Na
13 aluminium 1 27Al
15 phosphorus 1 31P
21 scandium 1 45Sc
25 manganese 1 55Mn
27 cobalt 1 59Co
33 arsenic 1 75As
39 yttrium 1 89Y
41 niobium 1 93Nb
45 rhodium 1 103Rh
53 iodine 1 127I
55 caesium 1 133Cs
59 praseodymium 1 141Pr
65 terbium 1 159Tb
67 holmium 1 165Ho
69 thulium 1 169Tm
79 gold 1 197Au
83 bismuth 0 1 209Bi

Elements with no primordial isotopes

No primordial isotopes
Longest-lived isotope > 1 day
t1⁄2[lower-alpha 7][1] Longest-
94 plutonium 8.08×107 yr 244Pu
96 curium 1.56×107 yr 247Cm
43 technetium 4.21×106 yr 97Tc[lower-alpha 1]
93 neptunium 2.14×106 yr 237Np
91 protactinium 32,760 yr 231Pa
95 americium 7,370 yr 243Am
88 radium 1,600 yr 226Ra
97 berkelium 1,380 yr 247Bk
98 californium 900 yr 251Cf
84 polonium 125 yr 209Po
89 actinium 21.772 yr 227Ac
61 promethium 17.7 yr 145Pm[lower-alpha 1]
99 einsteinium 1.293 yr 252Es[lower-alpha 6]
100 fermium 100.5 d 257Fm[lower-alpha 6]
101 mendelevium 51.3 d 258Md[lower-alpha 6]
86 radon 3.823 d 222Rn
No primordial isotopes
Longest-lived isotope < 1 day
t1⁄2[lower-alpha 7][1] Longest-
105 dubnium 16 h 268Db[lower-alpha 6]
103 lawrencium 11 h 266Lr[lower-alpha 6]
85 astatine 8.1 h 210At
102 nobelium 58 min 259No[lower-alpha 6]
104 rutherfordium 48 min 267Rf[lower-alpha 6]
87 francium 22 min 223Fr
106 seaborgium 14 min 269Sg[lower-alpha 6]
107 bohrium 2.4 min 270Bh[lower-alpha 6]
111 roentgenium 1.7 min 282Rg[lower-alpha 6]
112 copernicium 28 s 285Cn[lower-alpha 6]
108 hassium 16 s 269Hs[lower-alpha 6]
110 darmstadtium 12.7 s 281Ds[lower-alpha 6]
113 nihonium 9.5 s 286Nh[lower-alpha 6]
109 meitnerium 4.5 s 278Mt[lower-alpha 6]
114 flerovium 1.9 s 289Fl[lower-alpha 6]
115 moscovium 650 ms 290Mc[lower-alpha 6]
116 livermorium 57 ms 293Lv[lower-alpha 6]
117 tennessine 51 ms 294Ts[lower-alpha 6]
118 oganesson 690 μs 294Og[lower-alpha 6]
Periodic table with elements colored according to the half-life of their most stable isotope.
  Elements which contain at least one stable isotope.
  Slightly radioactive elements: the most stable isotope is very long-lived, with a half-life of over two million years.
  Significantly radioactive elements: the most stable isotope has half-life between 800 and 34,000 years.
  Radioactive elements: the most stable isotope has half-life between one day and 130 years.
  Highly radioactive elements: the most stable isotope has half-life between several minutes and one day.
  Extremely radioactive elements: the most stable isotope has half-life less than several minutes.

See also


  1. 1.0 1.1 1.2 See Stability of technetium isotopes and Stability of promethium isotopes for a detailed discussion as to why technetium and promethium have no stable isotopes.
  2. 2.0 2.1 2.2 Isotopes that have a half-life of more than about 108 yr may still be found on Earth, but only those with half-lives above 7×108 yr (as of 235U) are found in appreciable quantities. The present list neglects a few isotopes with half-lives about 108 yr because they have been measured in tiny quantities on Earth. Uranium-234 with its half-life of 246,000 yr and natural isotopic abundance 0.0055% is a special case: it is a decay product of uranium-238 rather than a primordial nuclide.
  3. 3.0 3.1 There are unstable isotopes with extremely long half-lives that are also found on Earth, and some of them are even more abundant than all the stable isotopes of a given element (for example, beta-active 187Re is twice as abundant as stable 185Re). Also, a bigger natural abundance of an isotope just implies that its formation was favored by the stellar nucleosynthesis process that produced the matter now constituting the Earth (and, of course, the rest of the Solar System) (see also Formation and evolution of the Solar System). In the case of argon the cosmically rarer 40Ar dominates on Earth over 36Ar as argon is too volatile to have been retained in the early proto-atmosphere of Earth while 40Ar is a decay product of long-lived and non-volatile 40K. Most argon in Earth's atmosphere is a product of potassium-40 decay. Most argon in the universe is not. At the present time 0.012% (120 ppm) of potassium on Earth is 40K. Taking the age of Earth and the half life of 40K (~1.25 billion years), this ratio was approximately an order of magnitude higher when the planet first formed. About 10.72% of that since-decayed 40K produced 40Ar, the rest having decayed to 40Ca.
  4. 4.0 4.1 4.2 While bismuth has only one primordial isotope, uranium has three isotopes that are found in nature in significant amounts (238U, 235U, and 234U; the first two are primordial, while 234U is radiogenic), and thorium has two (primordial 232Th and radiogenic 230Th).
  5. See many different industrial and medical applications of radioactive elements in Radionuclide, Nuclear medicine, Common beta emitters, Commonly used gamma-emitting isotopes, Fluorine-18, Cobalt-60, Strontium-90, Technetium-99m, Iodine-123, Iodine-124, Promethium-147, Iridium-192, etc.
  6. 6.00 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.10 6.11 6.12 6.13 6.14 6.15 6.16 6.17 6.18 6.19 6.20 For elements with a higher atomic number than californium (with Z>98), there might exist undiscovered isotopes that are more stable than the known ones.
  7. 7.0 7.1 Legend: yr=year, d=day, h=hour, min=minute, s=second.


  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Sonzogni, Alejandro. "Interactive Chart of Nuclides". National Nuclear Data Center: Brookhaven National Laboratory. 
  2. Marcillac, Pierre de; Noël Coron; Gérard Dambier; Jacques Leblanc; Jean-Pierre Moalic (2003). "Experimental detection of α-particles from the radioactive decay of natural bismuth". Nature 422 (6934): 876–878. doi:10.1038/nature01541. PMID 12712201. Bibcode2003Natur.422..876D. 
  3. Dumé, Belle (2003-04-23). "Bismuth breaks half-life record for alpha decay". Institute of Physics Publishing. 
  4. Siegel, Ethan. "Dark Matter Search Discovers A Spectacular Bonus: The Longest-Lived Unstable Element Ever" (in en). 
  5. "Noble Gas Research".  Novel Gas Research. Accessed April 26, 2009