edited by MARYVIRGINIA ORNA,0.S.U College of New Rochelle
P thumbnail hetchw Numbers in Chemical Names W. Conard Fernelius
Kent State University Kent. OH 44240 Althoueh evervone sooner or later has a Social Securitv number, many oliject to being identified by a number rathe; than by a name. On the other hand, there are those who are proud to be John David Fitzpatrick 111 or the equivalent. Chemical names frequentlv contain numhers. At times. the numbers are written out adin tetraphosphorus decaoxide, P4010, and at other times they appear as Roman numerals, phosphoms(V) oxide, PzOs, or as Arabic numbers in iron(3+) sulfate, (ZFe3+,3SOa). What do these numbers signify? Everyone recognizes that the Greek numerical prefixes tell how many atoms of each element are present in a molecule: (dikhlorine heptaonide for C120- and &trasulfur tetranitride for SJt. Only we cheat iusr a little bit and almost consistently leave out themono andoccasionally the di-: sulfur dichloridi for SC12, carbon dioxide for COz and (di)phosphoms pentasulfide for P2Ss. When it is necessary to distinguish two compounds of the same pair of elements, then the mono is often used: carbon monoxide for CO and sulfur monochloride for SCI (really SzC12). Many of the common metals such as sodium. calcium. and aluminum exhibit constant valencv in most of their compounds. In such cases, numerical prefixes are usuallv omitted: aluminum chloride. calcium sulfate. etc. Chemists make considerable use of a conceot known as the "oxidation number" which is usually expressed as a Roman numeral. This concept is useful in balancine equations for oxidation-reduction ieactions and for many other purposes. For nomenclature applications, the names chromium(III), oxide, Crz03, and chromium(V1) oxide, CrOs, are the equivalent of dichromium trioxide and (mono)chromium trioxide. Since Alfred Stock1 was the one who suggested the use of such numhers in names, the Roman numerals in parentheses are often called Stock numhers. There are many times when one wishes to designate the presence of ions in solids or their solutions. Ewens and Bassett2 suggested that this be done by Arahic numhers in parentheses: iron(2+) chloride, Fez+, 2C1-, and iron(3+) chlo-
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ride. Fe3+. 3C1-. These numbers are often known as Ewens~ a s s e tO t ~E-B numhers. They are particularly useful in those cases where there are two or more ions with identical or nearly identical composition but different charges: hydrazinium(l+)ion hydrazinium(Z+) ion uranyl(l+) ion uranyl(Z+)ion
Nz&+ NzHe2+ UOz+ UOz2+
Although the values of both Stock and Ewens-Bassett numbers have identical values in many cases, they must not be used interchangeahly. Although the uranyl(I1) ion has appeared in the literature, i t is a name without meaning. T o use stock numbers for U0z2+ would require the dioxouranium(V1) ion; the ion U2+ would be the uranium(I1) ion. The two kinds of numbers have specific, distinct, and very useful meanings. Note that both are written directly after the word t o which they refer without separation. Either Stock or E-B numhers are preferable to the old suffixes -ous and -ic to indicate oxidation state or charee on an ion. Full details of inorganic nomenclature can t ~ efound in publications of the International Union uf Pure and Amlied .. Chemistrv.' Less familiar are the so-called multiplicative prefixes his, tris. tetrakis. nentakis. etc. These are used esoeciallv to indicate a set of Gentical iadicals, each substituted in the same way: ~~~~~~~~
~
-
C,H,N=N
2.1-bis(pheny1azo)-1,knaphthalenediol
or to avoid ambiguity MHCeHQH4
P(C~oHnlr
ICdH~NCH&HDH&Isl
p-phenylenenebis(ke*ne) (diketen. sknifina dirner of ketene C H d O ) tris(decyl)phasphine (trideeylphaaphine would be CtsHnPHd tris(ethylenedisminel~obblt(3+) ion (triethvlenedisrnine is smbimoual
The use of these prefixes has been extended by many to "all complex expressions":
Whenever these multiplicative prefixes are used, the ex~ressionto which thev . aoolv . - .is enclosed in oarentheses or &her enclosing marks.
' Stock, A., Z. Angew. Chem., 32, 1, 373 (1919).
Ewens, R. V. G. and Bassett, H.. "Chemistry and Industry." 1949, 134, 137. "Nomenclature of Inorganic Chemistry." 2nd ~ d . .Bulterworths. London. 1970: Pure Appl. Chem.. 28[1], l(1971). The use of numbers as locants will form the basis of a future "Thumbnail Sketch."
964
Journal of Chemical Education
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BT e l d e s ~ r ~ p l i o01n phenomena, ~ topics, facts. etc u h ch chemical e d l d t r n s have lourn la be 01 ntoen in b i r teaching, wll a,presemed m a ' note rype 'formal thmugmui the Jamha.
