isotope effect

References

isotope effect

chemistry

Also known as: isotope shift, isotope structure, kinetic isotope effect(Show More)

Written by

The Information Architects of Encyclopaedia Britannica

Last updated

June 29, 2026

Quick Summary

The isotope effect in chemistry refers to the variation in certain characteristics of an element due to the mass differences of its isotopes. While isotopes of an element share the same chemical properties, their differing masses can subtly influence chemical reactions and physical processes.12

This effect is most noticeable when there's a significant mass difference between isotopes, such as between hydrogen (¹H) and deuterium (²H). The isotope effect can manifest in two primary ways:3

Primary Isotope Effect: This occurs when an isotope is located at the "reaction center" of a molecule, where chemical bonds are broken or formed. This can significantly alter the rate of the reaction.3
Secondary Isotope Effect: When an isotope is placed further from the reaction center, it produces a smaller change in the reaction rate.3

The magnitude of the isotope effect also depends on temperature; effects are generally more pronounced at lower temperatures. These subtle differences can be exploited in various applications, such as determining reaction mechanisms or inferring past temperatures from geological samples.452

Summary created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

5 Britannica Sources

Ask Britannica AI about this topic

Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.

reaction mechanism
Kinetic isotope effects
Isotopes are atoms that have the same atomic number (and, hence, generally the same chemistry) but different mass. The difference in mass becomes chemically important in certain instances. For example, when a carbon-hydrogen bond is replaced by a carbon-deuterium bond (deuterium being…
Read More
Isotopes are atoms that have the same atomic number (and, hence, generally the same chemistry) but different mass. The difference in mass becomes chemically important in certain instances. For example, when a carbon-hydrogen bond is replaced by a carbon-deuterium bond (deuterium being…
Read More

spectroscopy
Perturbations of levels
These effects are known as isotope shifts and form the basis for laser isotope separation. For light atoms, the isotope shift is primarily due to differences in the finite mass of the nucleus. For heavier atoms, the main contribution comes from the fact that the volume of the nucleus increases…
Read More
These effects are known as isotope shifts and form the basis for laser isotope separation. For light atoms, the isotope shift is primarily due to differences in the finite mass of the nucleus. For heavier atoms, the main contribution comes from the fact that the volume of the nucleus increases…
Read More

isotope
Physical properties associated with isotopes
…refer to the former as isotope effects and to the latter by a variety of more specialized names. The isotopes of helium afford examples of both kinds. Mass effects are considered first.
Read More
…refer to the former as isotope effects and to the latter by a variety of more specialized names. The isotopes of helium afford examples of both kinds. Mass effects are considered first.
Read More

hydrogen
Isotopes of hydrogen
…that the chemical differences between isotopes are negligible. For hydrogen, however, chemical reactions involving the different isotopes proceed at measurably different rates. These kinetic-isotope effects can be utilized in detailed studies of reaction mechanisms. The rates of reactions of compounds containing deuterium or tritium are usually less than those of…
Read More
…that the chemical differences between isotopes are negligible. For hydrogen, however, chemical reactions involving the different isotopes proceed at measurably different rates. These kinetic-isotope effects can be utilized in detailed studies of reaction mechanisms. The rates of reactions of compounds containing deuterium or tritium are usually less than those of…
Read More

hyperfine structure
…is called isotope structure, or isotope shift. These spectral lines are sometimes referred to as hyperfine structure but may be observed in an element with spin-zero isotopes (even atomic and mass numbers). Isotope structure is seldom observed without true HFS accompanying it.
Read More
…is called isotope structure, or isotope shift. These spectral lines are sometimes referred to as hyperfine structure but may be observed in an element with spin-zero isotopes (even atomic and mass numbers). Isotope structure is seldom observed without true HFS accompanying it.
Read More

BCS theory
…BCS theory also explains the isotope effect, in which the temperature at which superconductivity appears is reduced if heavier atoms of the elements making up the material are introduced.
Read More
…BCS theory also explains the isotope effect, in which the temperature at which superconductivity appears is reduced if heavier atoms of the elements making up the material are introduced.
Read More