Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. This means that isotopes of an element have the same atomic number but different atomic masses. Since the number of protons in the nucleus determines the element's identity, isotopes of an element have similar chemical properties but different physical properties due to their varying atomic masses.
Understanding isotopes is important in various scientific fields and has practical applications in medicine, industry, and environmental studies.