How is atomic mass calculated?

Atomic mass is calculated by considering the total number of protons and neutrons present in the nucleus of an atom. Protons have a positive charge and, along with neutrons, contribute to the overall mass of the atom, while electrons have negligible mass and do not significantly affect the atomic mass.

The atomic mass unit (amu) is defined such that one atomic mass unit is approximately equal to the mass of one proton or one neutron. Therefore, the atomic mass, often referred to as the atomic weight, essentially reflects the sum of these two components.

In essence, the mass of an atom is derived from the combined counts of its protons and neutrons, resulting in a straightforward calculation that highlights why the total of both these subatomic particles forms the basis for determining atomic mass.

While the average mass of all isotopes captures how atomic mass can vary across elements with different numbers of neutrons, the fundamental way of understanding atomic mass remains the presence of protons and neutrons in the nucleus.