SDSU Chemistry Placement Practice Test

Isotopes are forms of the same element that have the same number of protons but differing numbers of neutrons. This difference in neutron count does not affect the chemical behavior of the element since the defining characteristic of an element is the number of protons, which determines its atomic number. However, the varying neutron numbers lead to changes in atomic mass, as each neutron adds to the overall mass of the atom. This connection between isotopes and neutrons is crucial in understanding nuclear chemistry and radioactivity, as different isotopes of an element can have vastly different stability and physical properties. While isotopes ultimately can lead to different atomic masses due to the variation in neutron number, the most fundamental difference that defines an isotope is the number of neutrons in the nucleus. The other aspects, such as variations in the number of protons or electrons, do not define isotopes since those changes result in different elements or ions rather than isotopes of the same element.