Atoms and molecules are even smaller and exist in enormous numbers. Scientists use special quantities such as Relative Atomic Mass, Relative Molecular Mass, Avogadro Constant, and Mole to count them efficiently. Atomic Mass Unit (amu) The atomic mass unit is based on : 1/12 of the mass of a Carbon-12 atom. Relative Atomic Mass (Aᵣ) Definition : Relative Atomic Mass (Aᵣ) tells us how many times an atom is heavier than 1/12 of a Carbon-12 atom. Important : Relative Atomic Mass
