Written by the Fiveable Content Team • Last updated August 2025
Verified for the 2026 exam
Verified for the 2026 exam•Written by the Fiveable Content Team • Last updated August 2025
Definition
The mass number, represented by A, refers to the total number of protons and neutrons in an atomic nucleus. It helps identify isotopes since atoms with the same number of protons but different numbers of neutrons will have different mass numbers.
The atomic number represents the number of protons in an atom's nucleus. It determines an element's identity since each element has a unique number of protons.
Isotope: Isotopes are atoms of the same element that have different numbers of neutrons. They have the same atomic number but different mass numbers.
Nuclide: A nuclide refers to a specific atomic nucleus characterized by its proton and neutron count. It is identified by its atomic number and mass number.