A mole is a measurement of a ‘batch’ of particles. It is easier to describe the number of moles of a substance rather than the number of atoms as atoms are very small. Relative atomic mass is the ...
SUN Commission, Phys. Today, 15, 6, 20 (1962). Everling, F., König, L. A., Mattauch, J. H. E., and Wapstra, A. H., Nucl. Phys., 18, 529 (1960).