Final answer:
Isotopes are atoms of the same element that have different numbers of neutrons. They have the same number of protons and electrons, but differ in atomic mass.
Step-by-step explanation:
Isotopes are atoms of the same element that have different numbers of neutrons. All isotopes of an element have the same number of protons and electrons, which means they exhibit the same chemistry. The isotopes of an element differ only in their atomic mass, which is given by the mass number (A), the sum of the numbers of protons and neutrons.