isotope

American  

[ahy-suh-tohp] / ˈaɪ səˌtoʊp /

noun

Chemistry.

1. any of two or more forms of a chemical element, having the same number of protons in the nucleus, or the same atomic number, but having different numbers of neutrons in the nucleus, or different atomic weights. There are 275 isotopes of the 81 stable elements, in addition to over 800 radioactive isotopes, and every element has known isotopic forms. Isotopes of a single element possess almost identical properties.

---

isotope British  

/ ˌaɪsəˈtɒpɪk, ˈaɪsəˌtəʊp, aɪˈsɒtəpɪ /

noun

1. one of two or more atoms with the same atomic number that contain different numbers of neutrons

---

isotope Scientific  

/ ī′sə-tōp′ /

1. One of two or more atoms that have the same atomic number (the same number of protons) but a different number of neutrons. Carbon 12, the most common form of carbon, has six protons and six neutrons, whereas carbon 14 has six protons and eight neutrons. Isotopes of a given element typically behave alike chemically. With the exception of hydrogen, elements found on Earth generally have the same number of protons and neutrons; heavier and lighter isotopes (with more or fewer neutrons) are often unstable and undergo radioactive decay.

---

isotope Cultural  

1. In physics, different forms of the same element, with nuclei that have the same number of protons but different numbers of neutrons. Isotopes are distinguished from each other by giving the combined number of protons and neutrons in the nucleus. For example, uranium 235 is the isotope of uranium that has 235 protons and neutrons in its nucleus rather than the more commonly occurring 238. All elements have isotopes.

---

Other Word Forms

• isotopy
  noun
• isotopic
  adjective
• isotopically
  adverb

Etymology

Origin of isotope

First recorded in 1910–15; iso- + -tope, from Greek tópos “place”; cf. Utopia ( def. )

Compare meaning

How does isotope compare to similar and commonly confused words? Explore the most common comparisons:

• isotope vs. isomer

Explanation

An isotope of a chemical element is an atom that has a different number of neutrons (that is, a greater or lesser atomic mass) than the standard for that element. The atomic number is the number of protons in an atom's nucleus. Atomic mass adds to that the number of neutrons in the nucleus. Each element has a typical atomic mass, but when the number of protons stays the same and the number of neutrons changes, you have an isotope. These can be stable, like Deuterium, an isotope of Hydrogen that has one extra neutron, or they can be radioactive, like Plutonium-239, which is a component of nuclear waste.

Example Sentences

See Examples For:

isotope

Even so, the nickel isotope signature allowed the researchers to narrow the impactor down to a rare class of carbonaceous meteorite.

From Science Daily ● Jul. 19, 2026

Helium-3 is an isotope of helium, defined by the number of neutrons in the atom's nucleus.

From BBC ● Jun. 16, 2026

Published in Nature Communications, the research combines archaeology, ancient DNA analysis, isotope studies, and skeletal evidence to reconstruct how people lived, moved, ate, and buried their dead roughly 3,000 years ago.

From Science Daily ● May 19, 2026

Oklo noted Tuesday that its first isotope customer was “pending.”

From Barron's ● May 12, 2026

Here too, isotope analysis of his teeth solved the mystery, determining conclusively that his roots were not in England but in Italy.

From "Shipwrecked!" by Martin W. Sandler