List of elements by stability of isotopes

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

See also: List of nuclides, Stable isotope, Primordial nuclide, and Isotope § Nuclear properties and 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, 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 other rare types of decay, such as spontaneous fission or cluster decay are known. (See radioactive decay for details.)

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 83 elements in the periodic table, 80 have isotopes considered to be stable. Technetium, promethium (atomic numbers 43 and 61, respectively) 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 was the case in 2003 with bismuth-209, which had been considered to be stable). This list depicts what is agreed upon by the consensus of the scientific community as of 2008.

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 164 are energetically unstable, but have never been observed to decay. Thus, 254 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).

Of the chemical elements, only one element (tin) has 10 such stable isotopes, one (xenon) has eight isotopes, four have seven isotopes, nine have six isotopes, nine 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 29 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). An additional six 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 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, 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 isotopes. 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.

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 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. Of these, four elements (bismuth, thorium, uranium and plutonium) 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 (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; 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 339 nuclides are found naturally on Earth. These comprise 254 stable isotopes, and with the addition of the 34 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 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.

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. 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.

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 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.

Primordial isotopes (in order of decreasing abundance on Earth) of even-Z elements

Z	Element	Stable	Decays	unstable in italics odd neutron number in pink
50	tin	10	—	120Sn	118Sn	116Sn	119Sn	117Sn	124Sn	122Sn	112Sn	114Sn	115Sn
54	xenon	8	1	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
62	samarium	5	3	152Sm	154Sm	147Sm	149Sm	148Sm	150Sm	144Sm	146Sm
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
76	osmium	6	1	192Os	190Os	189Os	188Os	187Os	186Os	184Os
60	neodymium	5	2	142Nd	144Nd	146Nd	143Nd	145Nd	148Nd	150Nd
36	krypton	6	—	84Kr	86Kr	82Kr	83Kr	80Kr	78Kr
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
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	235U
4	beryllium	1	—	9Be
90	thorium	0	1	232Th
94	plutonium	0	1	244Pu

Primordial isotopes of odd-Z elements

Z	Element	Stab	Dec	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 in years/days

Z	Element	t1⁄2 of	Longest lived isotope
96	curium	1.56×107 a	247Cm
43	technetium	4.2×106 a	98Tc
93	neptunium	2.144×106 a	237Np
91	protactinium	32,760 a	231Pa
95	americium	7,370 a	243Am
88	radium	1,602 a	226Ra
97	berkelium	1,380 a	247Bk
98	californium	898 a	251Cf
84	polonium	103 a	209Po
89	actinium	21.77 a	227Ac
61	promethium	17.7 a	145Pm
99	einsteinium	1.29 a	252Es
100	fermium	100.5 d	257Fm
101	mendelevium	51.5 d	258Md
86	radon	3.82 d	222Rn
105	dubnium	1.3 d	268Db

No primordial isotopes
Longest lived isotope in hour/min/sec

Z	Element	t1⁄2 of	Longest lived isotope
104	rutherfordium	19 h	265Rf
103	lawrencium	11 h	266Lr
85	astatine	8.1 h	210At
107	bohrium	1.5 h	273Bh
106	seaborgium	1.1 h	272Sg
108	hassium	1 h	276Hs
102	nobelium	58 min	259No
87	francium	22.0 min	223Fr
113	ununtrium	20 min	287Uut
112	copernicium	8.9 min	285mCn
111	roentgenium	10 min	283Rg
109	meitnerium	6 min	279Mt
115	ununpentium	1 min	291Uup
110	darmstadtium	10 s	278Ds
114	flerovium	2.7 s	289Fl
116	livermorium	5.3×10−2 s	293Lv
117	ununseptium	7.8×10−2 s	294Uus
118	ununoctium	8.9×10−4 s	294Uuo

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.

  Stable elements: Elements which contain at least one stable isotope;

  Slightly radioactive elements: the most stable isotope is very long-lived, with half-life of over two million years;

  Moderately radioactive elements: the most stable isotope has half-life between 800 and 34,000 years;

  Highly radioactive elements: the most stable isotope has half-life between one day and 103 years;

  Significantly 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

• Table of nuclides
• Island of stability
• List of nuclides
• List of isotopes by half-life

Footnotes

• ^a See stability of technetium isotopes for a detailed discussion as to why technetium and promethium have no stable isotopes.
• ^b 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.
• ^c 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).
• ^d While bismuth and thorium only have one primordial isotope, uranium has three isotopes that are found in nature (238U, 235U and 234U; the first two are primordial, while ²³⁴U is radiogenic). Plutonium-244 is a special case because its half-life (80 Myr) is barely long enough to allow it to still be found in trace quantities on Earth.
• ^e 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.
• ^f 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.
• ^g Legend: a=year, d=day, h=hour, min=minute, s=second.
• ^h These values are not purely derived from experimental data, but at least partly from systematic trends.
• ⁱ Apart from flerovium and livermorium, elements with an atomic number above 112 have not yet been confirmed by IUPAC.