Numerous articles have been published that address problems encountered in teaching basic concepts of chemistry such as the atomic mass unit, Avogadro's number, and the mole. The origin of these problems is found in the concept definitions. If these definitions are adjusted for teaching purposes, understanding could be improved. In the present article, the definitions are discussed, and the following adjustments are suggested: (i) the feature that classifies carbon-12 for the definition as the standard be its abundance, (ii) Avogadro's number should refer directly to the standard nuclide sample, (iii) the definition of the mole be based on Avogadro's number, and (iv) the term "amount of substance" be replaced by the "collection" or "quantity of microentities". It is also proposed that the definition of the mole is first presented for nuclides and then generalized for poly-isotopic elements and chemical compounds. A possible redefinition of kilogram as a multiple of the standard nuclide mass is also briefly discussed. (Contains 1 table.)