A Proposition about the Quantity of Which Mole is the SI
Romeu C. Rocha-Filho' Universidade Federal de SHo Carlos, Caixa Postal 676. 13560-SHo The term mole was in use for about seven decades as a short word for "gram-molecular weight", when in 1961 Guggenheim proposed ( I ) that, instead, i t should be used for the unit of a new physical quantity: amount of substance. As soon as this nronosition was renorted. the name and meaning of this pdysical quantity were a matter of discussion and controversv that bv now have lasted over two decades (213). In thisnote, aker a brief review of the evolution of the meaning of the term mole and a discussion of intrinsic properties of matter, i t is proposed that the quantity measured usinn the SI base unit mole is numerousness, an intrinsic property of samples of matter. Some of the implications of accepting numerousness as the physical quantity whose SI u n i t k thk mole are also discussid. Mole: From a Concept to a Unlt As pointed out by Kieffer (14). as soon as the concept of atomic mass was established. chemists realized that samnles of different substances whose masses were in the same proportion as the respective molecular masses contained the same number of entities (molecules, atoms, or formulaunits). This, combined with the law of definite proportions and the fact that chemists usually work with mac~oscopic samples of substances, led to the introduction of the quantities"gram-molecular weight", "gram-atomic weight" and "gram-formula weight"2. According to Lybeck et al. (15), in 1889 Ostwald introduced the term "mole" to refer to "grammolecular weight"; shortly thereafter this term was already present in textbooks (16.17). In this century, the term "mole" slowly became more encompassing, becoming used also to refer to "gram-atomic weights" and "gram-formula weights" (18). On the other hand, an increasing emphasis was being put on the usage of quantity calculus (19-22,3), in whose calculations the mole appeared as a quantity unit. As a consequence of this last development, the following question became evident: "Of what quantity is the mole a unit?" The answer to this question led to a change of meaning of the term mole, from that of a concept to that of a unit of a specific physical quantity; according to Guggenheim ( I ) the term "mole" should he used to refer to the unit of the quantity amount of substance. Although, as mentioned above, the name and meaning of this physical quantity whose unit was called "mole" have been a matter of discussion (2-13) ever since Guggenheim proposed it, in 1971 "mole" became the seventh hase unit of Presented in part during the 9th Biennial Conference on Chemical Education, held by the ACS Division of Chemical Education, Bozeman, MT. July 1986. 'Currently (198911991) a visiting scientist at SRI International, Materials Research Lab.. 333 Ravenswood Ave.. Menio Park. CA 94025.
These quantities have also been referred to as "gram-molecule". "gram-atom", and "gram-formula". The noun "numerousness" is found on the rnajorlty of common dictionaries, while Its synonym "numerosity" appears only in large dictionaries, e.g., ref 25. Thus. "numerousness" is the word of choice, although its plural form is somewhat awkward.
Carlos, SP. Brasil the International System of Units for the hase quantity "amount of suhstance" (23). Numerousness: One of the Prooertles of Samples of Matter As pointed out elsewhere (241, every one of the samples of matter commonly handled by chemists has a mass, occupies a volume, and is a collection of extremely numerous entities. The quality of being numerous or many, or the state of consisting of a grea
