ARRT Practice Exam 2025 – All-in-One Guide to Master Your Radiologic Technologist Certification

Isotopes are defined as variants of a particular chemical element that have the same number of protons but different numbers of neutrons in their atomic nuclei. This characteristic is fundamental to understanding isotopes, as it determines their identity as the same element while varying in atomic mass. The number of protons in an atom defines the atomic number, which is what distinguishes one element from another; therefore, isotopes of a given element must have the same atomic number, meaning they possess the same number of protons.

The fact that isotopes have different numbers of neutrons results in variations in their atomic mass but does not affect the element's identity—hence they maintain the same chemical properties as they participate in chemical reactions similarly due to having the same electron configurations. While isotopes can exhibit some differences in physical properties, they generally maintain consistent chemical behavior within the same element. This understanding is key in fields such as nuclear medicine and radiology, where isotopes are frequently utilized for various applications. As a result, having the same number of protons is a defining feature of isotopes.