7. Any of the two or more atoms of the same element that have different numbers of neutrons. _______________

The term you're looking for is "isotopes."

Isotopes are variants of a particular chemical element that have the same number of protons but different numbers of neutrons, resulting in different atomic masses. For example, carbon has several isotopes, including carbon-12 (with 6 neutrons) and carbon-14 (with 8 neutrons). Because they have the same number of protons, isotopes of an element exhibit similar chemical properties, but their physical properties can differ, particularly in terms of stability and radioactive behavior. This concept is essential in fields such as chemistry, physics, and geology, especially in applications like radiocarbon dating and nuclear medicine.