provocative opinion Toward a More Rational Terminology R. J. Tyk0di Southeastern Massachusetts University, North Dartmouth, MA 02747
Perhaps because of historical "accidents," perhaps because of simpleinertia, because of reluctanie to tamper with established usage-for whatever reasons, it is nevertheless true that we chemists put u p with imprecise terminology in our discipline: we talk about "weights" that are not weights, "eauations" that are not eouatious. "molecules" that are not moiecules, etc. Although k e p r o f k o n a l chemists handle these imorecisions with imnunitv. the beeinnine student can h our-students would be get confLsed by i t all. ~ 0 t weand better served by a more rational terminology. Consider the following recommended changes in terminology. 1) atomic weight
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elemental mass, EM(. ..)
As our physicist colleagues never tire of telling us. "mass" and "weight" are two different concepts. Our Table of Values that lists argon as 39.943 is a table of the relative masses of the naturally occurring nuclides, relative to carbon-12 being exactly 12.0, averaged over the natural abuudances of the ineredient isotooes for each atomic numher. Now that is auite mouthful, and it is mercifully shorter to say that 39.938 is the "atomic weieht" of areon. But "weieht" eives the wrone idea; why not symply say,-"39.948 is the elemental mass argon, EM(Ar)-meanine therebv the comolete mouthful indicated above?
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2) molecular weight
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formula mass, FM(. . .)
The "molecular weight" is the sum of the "atomic weights" for the "atoms" in a formula. Why not dispense with this imprecise use of "weight" and say instead, e.g., "the formula mass of hydrogen chloride, FM(HCI), is the sum of the elemental masses of hydrogen and chlorine, i.e. FM(HC1) = EM(H) EM(C1) = 36.46"? Furthermore, the "molecular" part of the expression "molecular weieht" carries unwanted structural connotations. On the other gand, the expression "formula mass" is noncommital with respect to structure and leaves it to the context to establish whether we are dealing with a true molecule--e.g., HCl(g)-or with a ratio of ions-e.g., NaCl(s).
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3) gram atomic weight gram molecular weight gram formula weight
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mass per mole, MPM(. . .)
Elemental masses and formula masses are dimensionless quantities. In stoichiometric calculations, however, we need to know the masses of molar amounts of material, so we introduce the concept of mass per mole, MPM(. . .). Note that EM(Ar) = 39.948, whereas MPM(Ar) = 39.948 g mol-' = 0.039948 kg mol-'; and that FM(HC1) = 36.46, whereas MPM(HC1) = 36.46 g mol-1 = 0.03646 kg mol-1.
4) gram equivalent weight MPE(. ..)
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mass per equiualent,
Dispense with "weight" and say instead, ex.. "the mass per equivalent, of sulfur; acid, M P & H ~ S O ~ in ) , the acid-haw reaction H2S04 t 2h'aOH = NalS04 2H20 is '/1 its mass per mole. i.e. MPEIH.SO&I= '10 MI'MlH.,SO,) = 49.04 e eouiv-1
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5) specific heat unit heat capacity specific volume unit uolume specific gravity density Historically, a specific "something" was a comparison of the "something" property of a substance to the "something" property of water-specific "somethings" were thus dimenusaeey sionless numbers. Contemnoran, . ...however. has lareelv lost sight of the'.ratioWaspect ofspvr ific quantities, and we often see dimensional labek a%sienwlto snecific heats. swcific the whole"'can of volumes, and specific gravities-, worms" and say straight out what you mean: unit heat capacity ( J K-'g-I, J K-'kg-', etc.) or molar heat capacity ( J K-'mol-', etc.): unit volume (mL g-1, L g-1, m3kg-1, etc.) or molar volume (L mol-', m3 mol-', etc.); density (g mL-1, g L-', kg m-3, etc.).
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6) chemical equation
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reaction statement
We tell our students that the symbolic representation of a chemical reaction is a "chemical equation," and we insist that they learn how to balance chemical equations. Now mathematical equations never need balancing, so i t is a t first sight rather odd that chemical "equations" do need balancing. Why not simply say what the symbolic representation of a chemical reaction really is? It is a reaction statement, i.e., a statement telling how reactants combine to give products. Although "balancing a chemical equation" sounds a bit odd, "balancing a reaction statement" sounds like a perfectly reasonable thing to do.
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7) chemical equation in molecular form reaction statement in reagent form
When we transform a reaction equation from ionic form, e.g., Bas044 Ba2+(aq)+ SO?(aq) to an all-ions-paired form, e.g., BaCldaq) + HzSOdaq) BaSO4(s) + 2HCl(aq) we tell our students that we are "puttine the chemical eauation intomolecular form," but wecaution them that there.are no true "molecules" of BaCh or H-6 O a.or HCl liwimminn around in the aqueous solutioi. However, to judge from answers on quizzes and exams, many of them do believe that there are "molecular" swimmers thrashing around in the reaction swimming pool.
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Volume 62 Number 3
March 1985
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I t would be better to say that we are transforming the reaction statement from ionic form to reagent form, the form in which we would obtain the chemicals from a chemical stockroom or from a chemical supply house. If we are to be consistent with the abhreviation-forminn system indicated above, we will abbreviate "electromotiv~ force" as "EMF" rather than as "emf." If we adopt these recommended changes in terminology, we will be striking a blow for rationalitv and will be makina- our own lives and our students' lives a little easier. The recommended expressions "elemental mass," "formula mass," "mass per mole,.' and "mass per equivalent" are clearer indicators of the given concepts than the presently touted
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Journal of Chemical Education
expressions "atomic mass," "molecular mass," "molar mass,.' and "(gram) equivalent mass." Just think of the concept, the expression for the concept, and the ahbreviation for the exoression. I believe that after a little reflection you will see the advantages of my proposed list. Bv avoidine" the adiectival use of the words "atomic" and "molecular," we obviate certain sources of ambiguity or confusion. Mass-per-mole terminology gives us an umbrella expression that covers everything: we can talk about the mass per mole of oxygen atoms MPM(O), of oxygen molecules MPM(02), of sodium nitrate MPM(NaNOd, and so on. Finally, note that by using the abbreviation MPM(. . .) for mass-per-mole quantities we save plain M for its very satisfactory use as molarity M (moles liter-'). ~~
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