Atoms that have the same number of protons but different numbers of neutrons are called isotopes. For example, carbon has several isotopes: carbon-12, carbon-13, and carbon-14. While all of these isotopes have six protons (which is what defines them as carbon), they differ in their neutron count—carbon-12 has six neutrons, carbon-13 has seven, and carbon-14 has eight.
This difference in neutrons means that isotopes can have different atomic masses and can exhibit distinct chemical and physical properties, particularly in nuclear reactions. Understanding isotopes is essential in fields like chemistry, physics, and even medicine, where isotopes are used for imaging and treatment.