Leaving Certification Chemistry Practice Exam 2026 - Your All-in-One Guide to Exam Success!

Isotopes of an element are distinguished by the number of neutrons in their nuclei. While all isotopes of a particular element have the same number of protons, which defines the element itself, the variation in the number of neutrons results in different mass numbers. For instance, both carbon-12 and carbon-14 are isotopes of carbon; they have 6 protons but differ in the number of neutrons (6 in carbon-12 and 8 in carbon-14).

This difference in the number of neutrons directly leads to variations in atomic mass. Consequently, isotopes exhibit the same chemical behavior because they have identical electron configurations, but they may have different physical properties, such as stability and mass. Hence, understanding isotopes is crucial in fields like chemistry and nuclear physics, where the implications of varying neutron numbers can impact reactions and the behavior of substances.