Ohio Assessment for Educators (OAE) Integrated Science (024) Practice Exam

In isotope notation, how are isotopes represented?

1. Same number of protons and neutrons

2. Same number of protons, different number of neutrons

3. Different number of protons and neutrons

4. Same atomic mass

The correct answer is: Same number of protons, different number of neutrons

Isotope notation is designed to represent variants of an element that have the same number of protons but different numbers of neutrons. This is critical because the number of protons defines the element itself, while variations in the number of neutrons lead to different isotopes of that element, which can exhibit distinct physical and chemical properties. For example, carbon typically has six protons and six neutrons (carbon-12), but it also has isotopes like carbon-13 (six protons and seven neutrons) and carbon-14 (six protons and eight neutrons). Both carbon-13 and carbon-14 are isotopes of carbon, differentiated solely by their neutron counts. In contrast, options that mention the same number of protons and neutrons or differing numbers of protons and neutrons would not accurately represent the concept of isotopes. Isotope notation focuses specifically on the differences in neutrons while maintaining the same atomic number, which correlates directly to the number of protons. Hence, the correct representation is that isotopes have the same number of protons and different numbers of neutrons.