List of elements by stability of isotopes

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This is a list of the chemical elements and their isotopes, listed in terms of stability.

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 each other and protons equally by the strong nuclear force, 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.

However, 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 other rare types of decay, such as spontaneous fission or cluster decay are known. (See radioactive decay for details.)

Contents

Overview

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

Of the first 82 elements in the periodic table, 80 have isotopes considered to be stable.[1] Technetium, promethium (atomic numbers 43 and 61, respectively[a]) and all the elements with an atomic number over 82 have only isotopes that are known to decompose through radioactive decay. They are not expected to have any stable, undiscovered ones; therefore lead is considered the heaviest stable element. However, it is possible that some isotopes that are presently considered stable will be revealed to decay with extremely long half-lives (as was the case in 2003 with bismuth-209 which had been previously considered to be stable).[2][3] This list depicts what is agreed upon by the consensus of the scientific community as of 2008.[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 163 are energetically unstable, but have never been observed to decay. Thus, 253 isotopes (nuclides) are stable by definition (including Ta-180m, for which no decay has yet been observed). Those that are found in the future to be radioactive are expected to have half-lives usually longer than 1022 years (for example, xenon-134).

Of the chemical elements, only one element (tin) has 10 such stable isotopes, one (xenon) has eight isotopes, four 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.[1]

Additionally, about 29 nuclides of the 94 naturally-occurring elements have unstable isotopes with a half-life larger than the age of the Solar System (~109 years or more).[b] An additional 6 nuclides have half-lives longer than 80 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 253 (the stable nuclides) plus the 35 radioactive primordial nuclides, for a total of 288 primordial nuclides. This number is subject to change if new shorter-lived primordials are identified on Earth.

One of the primordial nuclides is Ta-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 7.7 x 1024 years of tellurium-128 was measured by a unique method of detecting radiogenic daughter xenon-128 and is presently the longest known experimentally measured half-life.[4] Another notable example is the only naturally-occurring isotope of bismuth, which has been predicted to be unstable with a very long half-life, but has only recently been observed to decay. Because of their long half-lives, such isotopes are still found on Earth in various abundances, and together with the stable isotopes they are called primordial isotopes. All the primordial isotopes are given in order of their decreasing abundance on Earth.[c]. For a list of primordial nuclides in order of half-life, see list of nuclides.

There are 80 elements with at least one stable isotope, but 114 to 118 chemical elements are known, depending on official confirmation (118 are given in this table). All elements to element 98 are found in nature, and the remainder of 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, four elements (bismuth, thorium, uranium and plutonium) are primordial because they have long enough half-lives to still be found on Earth,[d] 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 (assuming the total number of elements is 118) have isotopes with a half-life of at least 100 years. Every known isotope of the remaining 25 elements is highly radioactive; they are used in academic research and sometimes in industry and medicine.[e] Some of the heavier elements in the periodic table may be revealed to have yet-undiscovered isotopes with longer lifetimes than those listed here.[f]

About 339 nuclides are found in nature, on Earth. These comprise 253 stable isotopes, and with the addition of the 35 long-lived radioisotopes with half-lives longer than 80 million years, a total of 288 primordial nuclides, as noted above. The nuclides found naturally comprise not only the 288 primordials, but also include about 51 more short-lived isotopes (defined by a half-life less than 80 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.

Elements by number of primordial isotopes

An even number of protons or of neutrons are more stable (lower 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.

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 for strontium.

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.

Tables

The following tables give the elements with primordial nuclides, which means 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.

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).

The first table is for even-atomic numbered elements, which tend to have far more primordial nuclides, due to 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.

Primordial isotopes (in order of decreasing abundance on Earth[c]) of even-Z elements
Z
Element
Stabli
[1]
Decays
[b][1]
unstable in italics[b]
odd neutron number on pink
50tin10120Sn118Sn116Sn119Sn117Sn124Sn122Sn112Sn114Sn115Sn
54xenon81132Xe129Xe131Xe134Xe136Xe130Xe128Xe124Xe126Xe
48cadmium62114Cd112Cd111Cd110Cd113Cd116Cd106Cd108Cd
52tellurium53130Te128Te126Te125Te124Te122Te123Te120Te
62samarium53152Sm154Sm147Sm149Sm148Sm150Sm144Sm146Sm
44ruthenium7102Ru104Ru101Ru99Ru100Ru96Ru98Ru
66dysprosium7164Dy162Dy163Dy161Dy160Dy158Dy156Dy
70ytterbium7174Yb172Yb173Yb171Yb176Yb170Yb168Yb
80mercury7202Hg200Hg199Hg201Hg198Hg204Hg196Hg
42molybdenum6198Mo96Mo95Mo92Mo100Mo97Mo94Mo
56barium61138Ba137Ba136Ba135Ba134Ba132Ba130Ba
64gadolinium61158Gd160Gd156Gd157Gd155Gd154Gd152Gd
76osmium61192Os190Os189Os188Os187Os186Os184Os
60neodymium52142Nd144Nd146Nd143Nd145Nd148Nd150Nd
36krypton684Kr86Kr82Kr83Kr80Kr78Kr
46palladium6106Pd108Pd105Pd110Pd104Pd102Pd
68erbium6166Er168Er167Er170Er164Er162Er
20calcium5140Ca44Ca42Ca48Ca43Ca46Ca
34selenium5180Se78Se76Se82Se77Se74Se
72hafnium51180Hf178Hf177Hf179Hf176Hf174Hf
78platinum51195Pt194Pt196Pt198Pt192Pt190Pt
22titanium548Ti46Ti47Ti49Ti50Ti
28nickel558Ni60Ni62Ni61Ni64Ni
30zinc564Zn66Zn68Zn67Zn70Zn
32germanium4174Ge72Ge70Ge73Ge76Ge
40zirconium4190Zr94Zr92Zr91Zr96Zr
74tungsten41184W186W182W183W180W
16sulfur432S34S33S36S
24chromium452Cr53Cr50Cr54Cr
26iron456Fe54Fe57Fe58Fe
38strontium488Sr86Sr87Sr84Sr
58cerium4140Ce142Ce138Ce136Ce
82lead4208Pb206Pb207Pb204Pb
8oxygen316O18O17O
10neon320Ne22Ne21Ne
12magnesium324Mg26Mg25Mg
14silicon328Si29Si30Si
18argon340Ar36Ar38Ar
2helium24He3He
6carbon212C13C
92uranium02238U[d]235U
4beryllium19Be
90thorium01232Th
94plutonium01244Pu
Primordial isotopes of odd-Z elements
Z
Element
Stab
Dec
unstable: italics
odd N on pink
19potassium2139K41K40K
1hydrogen21H2H
3lithium27Li6Li
5boron211B10B
7nitrogen214N15N
17chlorine235Cl37Cl
29copper263Cu65Cu
31gallium269Ga71Ga
35bromine279Br81Br
47silver2107Ag109Ag
51antimony2121Sb123Sb
73tantalum2181Ta180mTa
77iridium2193Ir191Ir
81thallium2205Tl203Tl
23vanadium1151V50V
37rubidium1185Rb87Rb
49indium11115In113In
57lanthanum11139La138La
63europium11153Eu151Eu
71lutetium11175Lu176Lu
75rhenium11187Re185Re
9fluorine119F
11sodium123Na
13aluminium127Al
15phosphorus131P
21scandium145Sc
25manganese155Mn
27cobalt159Co
33arsenic175As
39yttrium189Y
41niobium193Nb
45rhodium1103Rh
53iodine1127I
55caesium1133Cs
59praseodymium1141Pr
65terbium1159Tb
67holmium1165Ho
69thulium1169Tm
79gold1197Au
83bismuth01209Bi

Elements with no primordial isotopes

No primordial isotopes
Longest lived isotope in years/days
Z
Element
t1/2 of[g][1]Longest
lived
isotope
96curium1.56×107 a247Cm
43technetium4.2×106 a98Tc[a]
93neptunium2.144×106 a237Np
91protactinium32,760 a231Pa
95americium7,370 a243Am
88radium1,602 a226Ra
97berkelium1,380 a247Bk
98californium898 a251Cf
84polonium103 a209Po
89actinium21.77 a227Ac
61promethium17.7 a145Pm[a]
99einsteinium1.29 a252Es[f]
100fermium100.5 d257Fm[f]
101mendelevium51.5 d258Md[f]
86radon3.82 d222Rn
105dubnium1.3 d268Db[f]
No primordial isotopes
Longest lived isotope in hour/min/sec
Z
Element
t1/2 of[g][1]Longest
lived
isotope
103lawrencium10 h[h]264Lr[f]
85astatine8.1 h210At
107bohrium1.5 h[h]273Bh[f]
104rutherfordium1.3 h265Rf[f]
106seaborgium1 h[h]272Sg[f]
108hassium1 h[h]276Hs[f]
102nobelium58 min259No[f]
87francium22.0 min223Fr[f]
113ununtrium[i]20 min[h]287Uut[f]
111roentgenium10 min[h]283Rg[f]
109meitnerium6 min[h]279Mt[f]
115ununpentium[i]1 min[h]291Uup[f]
112copernicium34 s285Cn[f]
110darmstadtium10 s278Ds[f]
114flerovium2.7 s289Fl[f]
116livermorium5.3×10−2 s293Lv[f]
117ununseptium[i]7.8×10−2 s294Uus[f]
118ununoctium[i]8.9×10−4 s294Uuo[f]
Periodic table colored according to the number of stable isotopes. Elements with odd atomic numbers have at most one or two stable isotopes, while elements up to lead with even atomic numbers all have three or more stable isotopes, except for the first three: helium, beryllium, and carbon.
Periodic table with elements colored according to the half-life of their most stable isotope.
  Elements which contain at least one stable isotope;
  Radioactive elements: the most stable isotope is very long-lived, with half-life of over four million years;
  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 103 years;
  Highly radioactive elements: the most stable isotope has half-life between one minute and one day;
  Extremely radioactive elements: the most stable isotope has half-life less than a minute. Very little is known about these elements due to their extreme instability and radioactivity.


See also

Footnotes

References

  1. ^ a b c d e f g h Sonzogni, Alejandro. "Interactive Chart of Nuclides". National Nuclear Data Center: Brookhaven National Laboratory. http://www.nndc.bnl.gov/chart/. Retrieved 2008-06-06. 
  2. ^ Dumé, Belle (2003-04-23). "Bismuth breaks half-life record for alpha decay". Institute of Physics Publishing. http://physicsweb.org/articles/news/7/4/16. 
  3. ^ Pierre de Marcillac, Noël Coron, Gérard Dambier, Jacques Leblanc, Jean-Pierre Moalic (April 2003). "Experimental detection of α-particles from the radioactive decay of natural bismuth". Nature 422 (6934): 876–878. Bibcode 2003Natur.422..876D. doi:10.1038/nature01541. PMID 12712201. 
  4. ^ http://presolar.wustl.edu/work/noblegas.html Novel Gas Research. Accessed April 26, 2009