What is the mass of an atom that includes its protons, neutrons, and electrons, typically expressed in atomic mass units?

The mass of an atom, which encompasses the sum of the masses of its protons, neutrons, and electrons, is typically expressed in atomic mass units (amu). This measure reflects the average mass of an element's isotopes weighted by their natural abundance and provides insight into the overall size and weight of an atom within the periodic table.

Atomic mass takes into account the contributions of all subatomic particles, with protons and neutrons contributing most of the mass due to their relatively large masses compared to electrons. Electrons have a negligible mass in comparison, but they are included for completeness.

Understanding atomic mass is vital for applications involving chemical reactions, stoichiometry, and the determination of molecular weights, which are fundamental concepts in chemistry. In contrast, the atomic number refers to the number of protons in an atom, the mass number defines the total number of protons and neutrons, and electron affinity measures the energy change when an electron is added to a neutral atom. Each of these has distinct meanings that do not pertain directly to the overall mass of the atom, making atomic mass the appropriate choice in this context.