ABSTRACT
Isotopes refer to elements with nuclei having the same number of protons, but differing
numbers of neutrons, so that the masses of contrasting isotopes differ by one to a few
neutrons. Isotopes of a specific element have the same chemical properties because they have the
same number of electrons. Owing to their mass differences, however, isotopes of an element
undergo chemical, biological, and physical reactions at slightly and consistently different
rates, leading to isotopic fractionation whenever reactants are not exhausted. As a result,
natural variations in isotopic abundance provide powerful insight into element dynamics, but
fractionation by intertwined transformations can also complicate interpretations.
