What defines an isotope?

An isotope is defined as atoms of the same element that have different numbers of neutrons. This means that they all share the same number of protons, which determines the element itself, but vary in their neutron count. This variation in neutrons results in different mass numbers for the isotopes. For example, carbon typically has six protons and six neutrons, making it carbon-12, while carbon-14 has six protons and eight neutrons. These differences can influence the stability of the atom and its behavior in chemical reactions, but they will still retain the same chemical properties because they are the same element.

The other choices do not encompass the definition of isotopes accurately. Atoms with the same number of protons will indeed define them as the same element, but it's the differing number of neutrons that distinguishes isotopes. While atoms with the same mass number can form isotopes, this is not the defining characteristic since isotopes can have different mass numbers. Lastly, the ability to bond easily is not related to the definition of an isotope, as bonding behavior is influenced by the electron configuration rather than the number of neutrons in the nucleus.