ABSTRACT
Definition The number of protons for any given element is unique. That is, all carbon atoms have only six protons (this is the atomic number); however, the number of neutrons is not unique. Most atoms of naturally occurring carbon contain six neutrons; these atoms have a mass number of 12. However, around 1.1% of all carbon atoms have seven neutrons, and therefore have a mass number of 13. Thus, atoms of an element that have the same number of protons but different numbers of neutrons are isotopes of that element. Isotopes of a particular element undergo identical chemical reactions.
