Glossary · Hóa học
Isotope
Atoms of the same chemical element that have the same number of protons but different numbers of neutrons, and therefore different mass numbers. Some isotopes are stable; others are unstable and undergo radioactive decay.
The number of protons, the atomic number Z, determines which element an atom belongs to. Isotopes of an element share the same Z but have different numbers of neutrons, and so different mass numbers A (protons plus neutrons). Carbon-12 and carbon-14, for example, both have 6 protons but have 6 and 8 neutrons respectively.
Stable isotopes do not change on their own; radioactive isotopes decay spontaneously over time. Most elements have more than one stable isotope. Adding even a single neutron can change an isotope's properties markedly: carbon-12 is stable, while carbon-14 decays.
Isotopes are used to trace natural processes through changes in isotope ratios. Radioactive isotopes also carry information about time, which is the basis of radiometric dating, such as carbon-14 dating.