Michigan Test for Teacher Certification (MTTC) Secondary Integrated Science Practice test

What defines isotopes?

1. Elements with the same atomic number and different atomic masses

2. Elements with different atomic numbers and the same mass

3. Elements with identical properties and structures

4. Elements that are chemically inert

The correct answer is: Elements with the same atomic number and different atomic masses

The definition of isotopes is based on the concept of atomic structure. Isotopes are variants of a particular chemical element that share the same atomic number, meaning they have the same number of protons. However, they differ in the number of neutrons, resulting in different atomic masses. This difference in neutron count leads to variations in mass, but the chemical properties of isotopes remain largely similar due to their identical number of protons and electrons. Hence, the definition emphasizes both the consistency in atomic number and the variability in atomic mass, which is fundamental in understanding isotopes in scientific contexts. The other options do not accurately capture this scientific definition. Differences in atomic numbers would indicate different elements entirely, while identical properties and structures, and being chemically inert, pertain more to categories of elements or states of matter rather than isotopic characteristics.