How is atomic mass expressed?

Atomic mass is primarily expressed in atomic mass units (AMUs), which provide a standardized way to compare the masses of different atoms. The atomic mass unit is defined as one twelfth the mass of a carbon-12 atom, and this unit allows scientists to represent the mass of an atom relative to this standard.

Using AMUs simplifies calculations in chemistry and physics because it directly pertains to the properties of atoms and molecules. For example, the atomic mass of an element indicated in AMUs can be directly related to the mass of a mole of that element in grams, thus linking molecular weight with practical measurement.

In contrast, expressing atomic mass in kilograms would not be practical for atomic-scale measurements, as kilogram is a much larger unit of mass. Liter volumes pertain to measurement of liquids and gases rather than atomic mass, and moles are a measure of substance quantity rather than a direct representation of atomic mass itself. Thus, AMUs are the most appropriate and widely accepted unit for expressing atomic mass.