American Registry of Radiologic Technologists (ARRT) Practice Exam

Which of the following refers to atoms that consist of the same atomic number but different mass numbers?

1. Isobars

2. Isotopes

3. Isotones

4. Yielding isotopes

The correct answer is: Isotopes

The term that describes atoms with the same atomic number but different mass numbers is isotopes. Isotopes are variants of a particular chemical element that have the same number of protons (which defines the element) but differ in the number of neutrons. This difference in neutrons results in different mass numbers for the isotopes of the element. For example, hydrogen has three isotopes: protium (with no neutrons), deuterium (with one neutron), and tritium (with two neutrons). Although all these isotopes are hydrogen and have the atomic number 1 (indicating one proton), their mass numbers differ due to their varying neutron counts. Other terms, such as isobars and isotones, describe different concepts. Isobars refer to atoms that have the same mass number but different atomic numbers, while isotones are atoms that have the same number of neutrons but different numbers of protons. Yielding isotopes is not a standard term used in nuclear chemistry or physics and does not accurately define any recognized category of atomic structure. Thus, isotopes is the correct and precise term for atoms with the same atomic number and differing mass numbers.