Q. What is Atomic Mass Units?

Ans. Notice in the last column of the table, the masses of the subatomic particles are reported in atomic mass units. The actual masses of electrons, protons and neutrons are so small and, consequently, inconvenient to work with. Therefore, scientists have developed a relative scale to report mass units. In this scale, a unit of mass is called the atomic mass unit, or amu. An amu is approximately the mass of one proton or one neutron. Since the mass of an electron is so small relative to the masses of the proton and neutron, it is assigned an atomic mass of 0 amu.

According to the International Union of Pure and Applied Chemistry (IUPAC), the mass of carbon-12 is exactly 12 amu. All other atomic masses are based on this standard.