REVISED INORGANIC (STOCK) NOMENCLATURE FOR THE GENERAL CHEMISTRY STUDENT ROBERT C. BRASTED University of Minnesota, Minneapolis
Arr~~ms t o reform and systematize inorganic nomenclature date to the early 1900's. Rosenheim and Koppel' suggested the use of arabic numerals in defining the number of atoms in a binary compound. Thus the oxide, Fe203,would be 2-iron 3-oxide. This system was severely criticized by Stock2and by Jordisa as being too cumbersome and having no advantages over the Brauner4 s u f i system (different suffixes for each of eight oxidation numbers). Even at this time the practice of using Roman numerals to define the oxidation state of an atom was common. In the 1920's, commissions and committees were formed t o examine the problem of nomenclature in detail. The recommendations of these bodies incorporated many of the suggestions of Stock and of Werner." The most comprehensive report, and probably to date the most authoritative, is that of the International Union of Pure and Applied Chemistry of 1940.8 The recommendations made by this body are essentially those that the writer wishes t o point up and t o urge strongly that teachers in secondary schools and colleges use in their instruction of nomenclature. The writer has had the pleasure of participating as a ROSENAEIM, A., AND I. KOPPEL,Chem.-Zlg., 33, 101-2, 11012 (1909). STOCK,A,, Chem. Ztg., 33, 205 (1909). a JORDIS, E., Chem. Zlg., 33, 162 (1909). ' BRAUNER, B., Z. anwg. Chem., 32, 10 (1902). STOCK,A,, Z. angew. Chem., 32(1), 373 (1919); 33(1), 79 A,, Angew. (1920); Angew. Chem., 47, 568 (1034). ROGENHEIM, M., Reform of the Nomencls, Chem., 33, 78 (1920). DELEP~NE, ture of Inorganic Chemistry (Report of Commission) Chem. Weekblad, 23,86 (1926). "ORISSEN, W. P., ET AL., J. Chem. Soe., 1940, 1404r15; J. Am. Chem. Soe., 63, 889 (1941); Ber., A73, 53-70 (1940). Scorn, J., Chem. Reus., 32, 73 (1943).
lecturer, director and/or co-director of a number of Summer Institute programs a t both the high school and college teachers' level, and has been dismayed a t the almost complete lack of knowledge by the registrants of the Stock (I.U.P.A.C.) recommendations in inorganic nomenclature. Actually, this situation is not surprising. Very few general chemistry texts and, to the best of the writer's knowledge, no high school texts even mention the revised inorganic nomenclature. Gengral review articles often have been largely limited t o the more specific areas of coordination compounds (applying Stock-Werner principles), published in journals not usually read by many of the freshman chemistry teachers, and certainly not available to the vast majority of secondary school science teachers. This discussion is intended to be a review of the general principles of Stock nomenclature. Some of its limitations and inadequacies are included, as well as certain proposals which can serve as extensions of the Stock system for adoption to ternary systems. There are advocates of the policy that a name is unnecessary, that a compound whose formula is not described by the classical prefixes and suffixes may simply be referred to either orally or in writing by formula. This writer is of the firm opinion that a compound should have a name, permitting even those with a minimum of training to transform this name to a formula. There are, of course, instances when the name may not be completely descriptive insofar as the crystal structure is concerned or where the stoichiometry is imperfect (as certain of the heavy metal oxides). As a generalization, it is suggested that the fewer the trivial names in inorganic chemistry, the better. The use of prefixes to define the atomic relationships
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(di-, tri-, etc.) is still acceptable to the Nomenclature Committee of the I.U.P.A.C.; however, even such prefixes lead to uncertainty in many cases. An example is the compound chlorine monoxide. Either CLO or CIO might represent the formula of such a compound. The writer encountered this ambiguity recently in searching Chemical Abstracts for information on C10. The abstractor of a particular article referred by formula to the compound "C10." The properties and chemistry were obviously meant to relate to ClzO. The original article proved that C120 was the compound under discussion and that it was named by the original author as "chlorine monoxide." The abstractor had taken the liberty of giving the formula "C10" throughout his abstract t o the compound "chlorine monoxide." A system of nomenclature should be sufficiently flexible to permit naming a compound whether or not it is stable or is presently known to exist. Thus, through methods not now known, it may be possible to prepare such compounds as FelOa, Fe03, ClBr,, AgCL, etc. No difficulty would be encountered in naming such compounds if the Stock system were generally used.
THE STOCK SYSTEM APPLIED TO TEACHING GENERAL CHEMISTRY NOMENCLATURE
Only the parts of the Stock syst,em are discussed here which appear t o be directly applicable t o the general or introductory course in chemistry. The more metallic element is named (without a suffix) followed by the oxidation state as a Roman numeral in parentheses. The anion is then named. A number of examples are cited in Table 1. TABLE 1 Some Binary Compounds Named Using Stock Nomenclature
Fonnula
Old name
CuCl CUCI? CUSO~ NiO Nil08 NiO, FeO Fe201 Pea04
Cuprous chloride Cupric chloride Copper trioxide Nickelous oxide Nickelic oxide Nickel dioxide Ferrous oxide Ferric oxide Magnetic oxide of iron (triiron tetraoxide) Chromoua oxide Chromic oxide Chromio anhydride (or chromium trioxide) Plumbous oxide, lead monoxide Lead trioxide (sesquioride), plumbous plumb-
CrO CmO. Cr01 PbO Pb201
ate
PbrO,
Lead tetroxide, red lead
MnCL Mn(0H).
Mengenaus chloride Manganese trihydroxide
. .
Stock name Copper(1) chloride Copper(I1) chloride Copper(II1) oxide Niekel(I1) oxide Nickel(II1) oxide Nickel(1V) oxide Iron(I1) oxide Iron(II1) oxide Iron(I1,III) oxide Chromium(I1 ) oxide Chromium(II1) oxide Chromium(V1) oxide Lesd(I1) oxide Lcad(II1) oxide, or Lead(I1, IV) oxide (see also Table 4) Lesd(I1, 11, IV) oxide (see rtlm Table 4) Mangmese(I1) chloride Mnnganese(II1) hydrox-
"
,
.
The examples above are sufficient in number to show the inconsistencies in the older nomenclature as well as the uniformity and simplicity of the Stock name. The highly unsatisfactory and ambiguous names for such an oxide as CrOa, chromic anhydride or chromium trioxide (CrzOawould also be named chromium trioxide), are no VOLUME 35, NO. 3, MARCH, 1958
longer needed. The student is not confronted with i n abrupt end t o his system of using -ous and -ic suffixes when more than two oxidation levels are encountered for a given metal. The writer is suggesting (and indeed the recommendation haq been made by the I.U.P.A.C.) that the Stock system be extended to such oxides noted above as Fe304and Pbt04. No claim is made that the use of the name iron(I1,III) oxide for the compound Fe301 describes the crystalline state; likewise for the compound Pb,Ol. The use of the two Roman numerals (11) and one numeral (IV) will show that the ultimate ratio of lead and oxygen atoms is 3 : 4. If the compound is t o be named as a lead salt, the Stock system serves very adequately (see Table 4). The -om and -ic suffixes have been sanctioned by the I.U.P.A.C. when no ambiguity is possible. The author feels that even for such metal ions as Cu+, Cu++,Fe++, Fe+a,Hg2++,Hg++, Co++ and C O + ~the , Stock system should be adhered t o and the system used consistently throughout any paper, text, or article. Certainly oxidation levels greater than + 2 for copper are known, as well as levels greater than +3 for iron and cobalt are known. The chemistry of Ag(I), Ag(I1) and Ag(II1) compounds also points to the need and convenience of Stock principles. The definition of -ic as the higher oxidation state is thus not only noninformative but misleading. The name cupric chloride for CuCL is to the first year chemistry student, then, little better than a trivial name. The existence of suboxidation levels for such elements as silicon and aluminum, though probably not mentioned in many general chemistry texts, must certainly be recognized. A suitable systematic nomenclature should be a t hand to permit naming compounds in which such oxidation levels exist. The compounds SiO and A10 are simply named silicon(I1) oxide and aluminum(I1) oxide, respectively. The author readily concedes that the designation of oxidation levels for ordinarily nonvariant metals as those in Groups IA and IIA, as well as aluminum, is usually unnecessary. The Stock system does permit the definite specification of oxidation level when needed. APPLICATION OFISTOCKNOMENCLATLTRETO BINARY COMPOUNDS O r NONMETALS WITH NONMETALS
There is no reason why compounds resulting from the combination of nonmetals with nonmetals should not be named applying the same principles as applied for metals in combination with nonmetals. Some examples of the former type compounds are given in Table 2. The constancy of the -2 oxidation level of combined oxygen leaves no ambiguity in the formulation of the oxides from the Stock name. Thus, chloriue(1V) oxide could not be written other than ClO,, whereas chlorine dioxide might be CIOn or CI2O1. The latter would be named as the dimer of chlorine(I1) oxide. Chlorine trioxide might be C103or Cl,Oz. An anomaly does arise in the naming of oxygen difluoride, OF,, by the Stock system. The oxygen atom is probably more electropositive than fluorine; however, one is reluctant to assign a positive two oxidation state t o the oxygen. The recommended name would then be oxygen difluoride.
TABLE 2 Stock Names for Some Nonmetal-Nonmetal Compounds Fornula
Stock name
Cl10 C1,Oa CIOn ClsOs Ns0 NO* NnOa NzOs PCls POCI, IF, PCI, SCll SF, SFs
Chlorine(1) oiide Chlorine(II1) oxide Chlorine(1V) o ~ i d e Dimer of chlonne(V1) oxide Nitrogen(1) oxide Nitrogen(1V) oxide Dimer of nitrogen(1V) oxide Nitrogen(V) oxide Phosphorus(II1) chloride Phosphorus(V) oxychloride Iodine(VI1) fluoride Phasphorus(V) chloride . Sulfur(I1) ohlor!de Sulfur(1V) fluorlde Sulfur(V1) fluoride
The designation of the oxidation level by the Roman numeral does not constitute a dogmatic statement as t o the degree of ionic valency of the metal-nonmetal bond. The fact that nitrogen in nitrogen(I1) oxide and the copper in copper(I1) oxide are both divalent need not mean that the oxides are equally ionic. A Stock name is only intended to permit the unambiguous formulation of a given compound. The use of the pw-prefix for true peroxy compounds or peroxides is still desirable. It would be erroneous to name BaOz as barium(1V) oxide or NazOzas sodium(I1) oxide. An improvement in peroxide nomenclature to permit clear formulation and differentiation from oxides is needed. The oxides and peroxides of potassium; KzO, KzOz, K203,KO%,(KzOJ and KO3 are difficultto name by any of the presently accepted systems. Prefixes such as mono-, di-, tri-, etc., would be needed. THE APPLICATION OF STOCK-WERNER SYSTEM TO COMMONLY ENCOUNTERED COMPLEX ENTITIES
The principles of the Stock-Werner system are herein discussed which permit the first year student to name complexes most likely t o be encountered in general chemistry and qualitative analysis. Certain complex entities composed of organic chelate groups, bridged complexes and polynuclear systems, need not be and usually are not considered in the first year course. The suffix for all anionic complexes is -ate. The suffix for all complex acids is -ic. The metal atom (ionically associated as a cation with the complex) is named first followed by its oxidation state as a Roman numeral in parentheses. The complex anion is next named. The number of coordinated groups is designated using prefixes mono-, di-, tri-, etc. The central metal is then designated using t,he-ate suffix, followed by the oxidation state of this atom as a Roman numeral in parentheses. A specific example is Cu3[Fe(CN)~I2. The name is copper(I1) hexacyanoferrate(II1). Negative ions (ligands) coordinated to the central metal are assigned an o suffix as: NOz-, nitro; C1-, chloro; I-, iodo; CN-, cyano; OH-, hydroxo; C03--, carbanato. The NHJ ligand is ammine and H 2 0 is aquo. When both negative and neutral groups are coordinated to a central metal atom, the negative group(s) is named first, followed by the neutral ligand(s), then the central atom, followed by the oxidation state. An example is [ C O ( N H ~ ) ~ C ~ ~named ] C I , as dichlorotetraammineco-
balt(II1) chloride. Table 3 includes exanlples of negative, neutral, and positive complexes. TABLE 3 Nomenc1atu.e of Some Complex Entities Stock-Werner name
Sodium tetrschlorostannate(J1) Sodium hexachlorostannate(1V) Hexachlomplatinate(1V) ion Tetrachlomplatinic(I1) acid Dicyanocuprate(1) ion Heuacyanoierrate(I1) ion Hexanitrocohaltate(II1) ion Carhan~totetrammine~ohalt(II1) ions Trichlorotriammineeobalt(II1) Tetraquocadmium(I1) ions Hexachlorostihnate(V) ion Tetramminezinc(I1j chloride' Sodium tetrahydroxoaluminate(II1) The a of tetra may he omitted when followed by ammine or aquo.
I n practice, the designation of the oxidation level of the zinc and aluminum for the two last-mentioned complex compounds above is unnecessary due t o the nearly nonvariant oxidation levels of these two central metal atoms. For consistency in naming complex entities it seems advisable t o designate the oxidation levels of the central atom in all cases. The use of aqw, for coordinated water molecules is in slight variance with the I.U.P.A.C. recommendation that negative ligands use an o suflix. SUGGESTED ADOPTION OF STOCK-WERNER SYSTEM TO COMMON OXY-ANIONS
The writer wishes t o present (for comment and criticism) an extension of the Stock-Werner system to oxy-anions. There is nothing essentially new in this extension, since the suffix for all anions would still be -ate, and the oxidation state of the central atom would be designated by the Roman numeral. When an ion may have more than one form (as in the ortho, meta, or pyro hydration states) it would be possible to designate the number of associated oxygen atoms by 0x0. When no confusion is likely to result (as in the case of NOa-, SO4--, SOa--) the 0x0 term would be neglected. Table 4 includes some examples. The list could be continued. By way of criticism, it is admitted that for those who have spent their professional careers using the classical names of ions and who know the chemistry of the elements involved, the designation by the 0x0 term would seem cumbersome and unnecessary; however, with the e\-er-broadening field of inorganic chemistry even those trained in this overall area have trouble in keeping up with the literature in all of the chemistry of the metals. It is further recognized that in certain of the thio and polythioanious, no single oxidation state for the sulfur exists. The use of the average oxidation state is indicated in certain examplesin the above table. In defense, the writer would prefer the use of the average state rather than to assign a trivial name to the ion. Advantages are obvious in eliminating the per- prefix to the Group VII metal and nonmetal oxyanions. This prefix has so long been confused with the peroxy prefix (as SOs-- for peroxymonosulfuric acid). Since it is common and necessary to refer to many of JOURNAL OF CHEMICAL EDUCATION
TABLE 4 Suggested Nornenclatu~e of Some Anions Using StockW e r n e ~Principles
Cuprate(I1) ion Heryllate(I1) ion Aluminate(II1) ion (or dioroalominnt,r(III) ion) Stannate(1V) ion Zlitrste(II1) ion Xitrate(V) ion PIumbate(I1) ion (Pb(l'I,0?)2 rr-onld hc 1,cad (17') plumhate(I1) Dihydrogenphosphate(1) ion Metaphosphate(V) ion (ort~.iozol,hosphnt,r(V) inn)
~h%ate(111) ion Chromate(V1) ion Mangenate(V1) ion Manganate(VI1) ion Chlorate(1) ion Chlorate(V) ion Iodate(VI1) ion Hexaoxoiadate(VI1) ion (instend of paraperiodate) Thioasenate(II1) ion Thioarsenate(V) ion Oxotrithioanenate(V) ion Sulfate(I1) ion Sulfate(1V) ion Sulfate(II1) ion (or tetrao~odisulfate(II1)ion)
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the transition metal atoms in their various oxidation states, the Stock system provides a convenient medium, as Cr(V1) in the GO4-- ion, Mo(1B) in the Moo8--, or Mo(VI) in Moo4--. The problems in the polyphosphates, polysilicates, hetero and isopoly ions, etc.; are still real. However, a combination of Stock and Werner principles would greatly simplify t,he names. A similar situation exists in the orgmo-metnllics where Rock nomenclature is npplicnble. RECOMMENDED ATOMIC SYMBOL DESIGNATION
The writ.er desires t o re-emphasize the recommendation of the I.U.P.A.C. in at,om symbols. Actually t,here is only one change, in that the mass number is to he placed above and t o the left of the symbol. This practice is contrary t.o that used for many years by the nuclear chemist and physicist. There is the obvious advantage in following the recommendation of leaving the space to the right and above the symbol for the ionic charge. Examples are: :He++ for the alpha particle; and :Hz+ for a tritium molecule-ion. In conclusion, it may be stated that the student beginning or even well into his chemical training must be given a dual "treatment" since he must know classical systems. The instruction in Stock and Stock-Werner nomenclature should require very little additional time or effort.
