Yes, mass is often expressed in atomic mass units (amu) in the context of atomic and molecular weights. The atomic mass unit (amu) is a unit of mass used to express the relative masses of atoms and molecules. It is defined as 1/12th the mass of a carbon-12 atom.
To be more precise, 1 amu is equal to one-twelfth the mass of a carbon-12 atom, which is approximately equal to 1.660539040 × 10^−27 kilograms. The choice of carbon-12 as the reference isotope is because it has a mass close to 12 atomic mass units, making it a convenient reference point for atomic mass measurements.
Using atomic mass units allows scientists to express the masses of atoms and molecules in a more convenient and manageable manner, as the actual masses of atoms and molecules in kilograms can be extremely small and difficult to work with in practical calculations.
In addition, the atomic masses listed on the periodic table are relative atomic masses expressed in atomic mass units. They represent the average masses of all the naturally occurring isotopes of an element, taking into account their relative abundances.