List of elements by stability of isotopes.html



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

See also: Isotope#Nuclear properties and stability

Atomic nuclei consist of protons and neutrons, which attract each other through the strong 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 offsetting 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 spontaneous fission.

Overview

Isotope half lifes. 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. However, it is possible that some isotopes that are presently considered stable will be revealed to decay with extremely long half-times (as was the case in 2003 with bismuth-209 which had been previously considered to be stable).²³ 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. Of these elements, only one (tin) has 10 stable isotopes, one (xenon) has nine, five have seven, three have six, nine have five, eight have four, 11 have three, 15 have two, and 27 have a single stable isotope.¹ Additionally, 28 of these 80 elements also have unstable isotopes with a half-life longer than the age of the Solar System (~>10⁹ years).^[b] Because of their long half-times, these 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]

The other 37 discovered elements have isotopes which are all known to be radioactive. The elements in this list are ordered according to the lifetime of their most stable isotope.¹ Of these, four (bismuth, thorium, uranium and plutonium) are primordial because they have long enough half-times to still be found on Earth,^[d] while all the others are produced either by radioactive decay or are synthesized in laboratories. Only 13 of these 37 elements have isotopes with a half-time of at least 100 years. Every known isotope of remaining 24 elements is highly radioactive, and not used outside of academic research.^[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]

Elements with stable isotopes

Periodic table colored according to the number of stable isotopes. Elements with odd atomic numbers tend to have fewer stable isotopes than their even-numbered neighbours.

Elements without stable isotopes

Periodic table colored according to the half-lives of their most stable isotope .      Stable elements;      Radioactive elements with very long-lived isotopes. Their half-live of over four million years confers them very small, if not negligible radioactivities;      Radioactive elements that may present low health hazards. Their most stable isotopes have half-times between 800 and 34.000 years, which give them radiation levels around the background level. Because of this, they usually have some commercial applications;      Radioactive elements that are known to pose high safety risks. Their most stable isotopes have half-lifes between one day and 103 years. Their radioactivities confers them little potential for commercial uses;      Highly radioactive elements. Their most stable isotopes have half-lifes between one day and several minutes. They pose severe health risks and is unlikely that they will receive uses outside basic research;      Extremely radioactive elements. Very little is known about these elements due to their extreme instability and radioactivitiy.

See also

• Table of nuclides
• Island of stability

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 may still be found on Earth, but only those with half-lives above 10⁹ are found in appreciable quantities. The present list neglects a few isotopes that are found in the 10⁸-10⁹ range because they have not been measured in apreciable quantities on Earth.
• ^c There are unstable isotopes with extremely long half-times that are also found on Earth, and some of them are even more aboundant than all the stable isotope (such as ¹¹⁴Cd). Also, a more abundant isotope on Earth does not necessarily imply that the isotope is the lowest in energy and therefore the most stable. It just implies that their formation was favored by the stellar nucleosynthesis precessed that produces the matter constitutes now the Solar System and the Earth (see also Formation and evolution of the Solar System).
• ^d While bismuth and thorium have only one primordial isotope, uranium has three isotopes that are found in nature (²³⁸U,²³⁵U and ²³⁴U). Plutonium is a special case because its half-time is barely enough to allow it to still be found in trace quantities on Earth.
• ^e Americium with a half life of over 7000 years is the least stable element that is used in commercial applications (fire alarms).
• ^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 None of the elements with an atomic number above 111 have yet been confirmed by IUPAC.

References