What is the atomic mass of an element? Atomic massAtoms are extremely small; the heaviest atoms have masses of about 10–22 g. Even an ultramicrobalance cannot measure the mass of a single atom. However, relative masses of atoms of different elements can be determined. At first, the mass of the lightest atom, hydrogen. The SI unit for mass is kilogram (kg). The mass … [Read more...] about What is the atomic mass of an element?