Every element comes in several versions called isotopes, which differ only in their number of neutrons. This table counts the 3,383 known isotopes of the 118 elements, 244 of them stable, and gives the most common isotope and the longest-lived radioactive isotope of each element.
Half-life units: y years (ky thousand, My million, Gy billion years), d days, h hours, min minutes, s seconds. A dash means the element has no isotope with a measured natural abundance. Data: IAEA Live Chart of Nuclides.
What is an isotope?
Atoms of one element always have the same number of protons, but their number of neutrons can vary. Each variant is an isotope. Carbon-12 has 6 protons and 6 neutrons, while carbon-14 has 6 protons and 8 neutrons. The number after the name is the mass number: protons plus neutrons. Isotopes of an element behave almost identically in chemical reactions, but they differ in mass and in nuclear stability.
Stable and radioactive isotopes
A stable isotope has never been observed to decay. 244 isotopes are stable, and 38 elements have none at all: technetium, promethium and every element from bismuth onward. Tin has the most stable isotopes, 10. All other isotopes are radioactive: their nuclei turn into other nuclei by emitting particles or radiation.
Half-life
The half-life is the time it takes for half of a sample of a radioactive isotope to decay. It ranges from far less than a second to far longer than the age of the universe. Bismuth-209 decays so slowly that it was thought to be stable until 2003.
Natural abundance and atomic mass
Most elements occur in nature as a fixed mixture of isotopes. The share of each one is its natural abundance, and the atomic mass printed on the periodic table is the average of the isotope masses weighted by abundance. Chlorine is about 76% chlorine-35 and 24% chlorine-37, which gives its atomic mass of about 35.45.
The Isotopes view of the interactive periodic table fans out all the isotopes of any element, with half-life, decay mode and abundance.
This table lists 3,383 known isotopes of the 118 elements, of which 244 are stable. New short-lived isotopes are still being made in particle accelerators.
Which element has the most stable isotopes?+
Tin, with 10 stable isotopes.
Which elements have no stable isotopes?+
Technetium, promethium and every element from bismuth (83) to oganesson (118): 38 elements in total.
Do isotopes of an element have different chemical properties?+
Hardly. Chemical behaviour depends on the electrons, and all isotopes of an element have the same number of electrons. They differ in mass and in nuclear stability, and the mass difference matters most for the lightest elements, such as hydrogen.