noun Chemistry.

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.

Origin of isotope

1910–15; iso- + -tope < Greek tópos place
Related formsi·so·top·ic [ahy-suh-top-ik] /ˌaɪ səˈtɒp ɪk/, adjectivei·so·top·i·cal·ly, adverb Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for isotope

Contemporary Examples of isotope

Historical Examples of isotope

  • Why nail the "power metal" down to an isotope of gold with an atomic weight of 197?

    Despoilers of the Golden Empire

    Gordon Randall Garrett

  • An isotope is just a different variety of the ordinary kind of atom in each element.

  • There must be another one in either wing, for the isotope plant and the cartridge-case plant.

    The Cosmic Computer

    Henry Beam Piper

  • Well, heavy water is made of one atom of oxygen plus two atoms of deuterium, which is the first isotope of hydrogen.

British Dictionary definitions for isotope



one of two or more atoms with the same atomic number that contain different numbers of neutrons
Derived Formsisotopic (ˌaɪsəˈtɒpɪk), adjectiveisotopically, adverbisotopy (aɪˈsɒtəpɪ), noun

Word Origin for isotope

C20: from iso- + Greek topos place
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for isotope

1913, literally "having the same place," introduced by British chemist Frederick Soddy (1877-1956) on suggestion of Margaret Todd, from Greek isos "equal" (see iso-) + topos "place" (see topos); so called because despite the different atomic weights, the various forms of an element occupy the same place on the periodic table.

Online Etymology Dictionary, © 2010 Douglas Harper

isotope in Medicine




One of two or more atoms having the same atomic number but different mass numbers.
Related formsi′so•topic (-tŏpĭk) adj.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

isotope in Science



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.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

isotope in Culture



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.

The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.