What does the term "mass number" specifically refer to in chemistry?

The term "mass number" specifically refers to the total number of protons and neutrons in an atom. This value is significant because it provides information about the combined mass of the nucleus, which is primarily determined by these two types of particles, as neutrons and protons have a much greater mass compared to electrons. The mass number is crucial for identifying isotopes of an element, as different isotopes have the same number of protons (and hence the same atomic number) but different numbers of neutrons, leading to variations in mass number.

Understanding mass number helps in various areas of chemistry, including nuclear reactions and the study of isotopes, which can be important in fields ranging from medicine to archaeology. The mass number does not involve the electron count or the average atomic mass, which are separate concepts with distinct implications in chemistry.