Teaching Inorganic Nomenclature

A Systematic Approach

Gerhard Lind Metropolitan State College, 1006 11th Street, Denver, CO 80204

Naming inorganic compounds seems to be unsystematic, unim~ortant. and subiect to Dure memorization. This im- presgon is ;navoidaLle when the leading textbooks for eeneral chemistnr in the United States are renewed ( I - 12). From discu&ions with many colleagues, I also feel that many instructors who teach general chemistry do not know the subject of naming inorganic compounds well enough to teach i t adequately and therefore either do a rather poor job or avoid the subject altogether.

Being able to name inorganic compounds is, in my opin- ion, something every student should master after complet- ing one year of college-level general chemistry. Since I am not an advocate of memorization, I decided to look for the systematics in inorganic nomenclature. I would like to present a semisystematic scheme that I have used success- fully for the past four years in our entry-level (college freshmen, general chemistry course.

The scheme is divided into three parts: Cations, Anions, and Compounds tsce Figs. 1 3 , . Cations are further subdi- vided into monatomic and polyatomic; anions, into mon- atomic, oxyanions, others and exceptions, and oxyanions containing hvdronen. Compounds are suhdivided into ionic compoun&, iompounds containing hydrogen, and covalent compounds.

I am aware that dividing inorganic compounds into "ionic" and "covalent" compounds and then having as a

third category "compounds containing hydrogen" may be a little problematic and artificial, but for the purpose of namiie com~ounds it is not. and the fine tuninn can al- ways b;e done in class when the subject is discussGd.

Students have eenerallv reacted oositivelv to the scheme, and the re& as deasured b i the students' per- formance on the subject in examinations are encouraging.

Literature Cited 1. Atkins,P. WDpnwdChemistry, 11ted.;SdentficAmerierierinB~~kk:NkwY~rk,1989. 2. Bodner. 0. M.: Pardue. H. L. Chomislw. an Errnri"mta1 S c b b . 1st ed.: Wilev:

N ~ W Y O ~ 198s. 3. Brady, J E.: Humistan, G . E. Genrml Chernistry:P%cipk8 ondSnudum, 4th ed.;

Wiley: New York, 1986. 4. Brown, T. L.: LeMay H. E., Jr Chemistry: The Centrnl Scbnco, 4th ed.; Prentiee

Hell: Engleurood CliIT8,NJ. 1988. 5. Chang, R. ChemL?try. 3rd ed.; Random Hauae: NewYark, 1988. 6. Ebbing, D. D.: Wrighton, M. S. &mrd Chemistry, 2nd dd.; Houghton Mifflin: Boe-

ton. MA, 1987. 7. oillespie, R. J.; H-phreys, D. A ; Baird, N. C.; Robinson, E. A. Chemistry, 2nd 4.;

Ally" and Bamn: Needham Heighlghts, MA, 1989. 8. KO*, J. C.; Pureell, K F Chprnlsby ond Chamiml Remfiuify. 1st ed.; Sauoders:

PhBadelohia. PA. 1987. . . . 9. M @ u . ~ . , OA: Raek,PA. Gemrdchomisfry, 2nd ed.; W H. Freeman: NyYork,

1917

. . ~ ~ d l a l a : New York. 1989.

11. Whit*", K. W; Gsiley, K . D.: Davis, R. E . Gonrml chpmistry, 3rd ed.: Saunders: Philadelphia, PA, 1988.

12. Zumdahl, S. S. Chemistry, 2nd ed.; Heath: Lexington, MA, 1989.

Only One Ion More Than One Possible ion Possible

Rule: Name of element + 'ion.'

Examples: Na* sodium ion Ma2* maonesium ion H' hydiogen ion

Comment: The number of positive charges is not indicated in the name because it is not necessary

Rule: (a) newer rule: positive charoes indicated bv 1 i a roifian numeral. I I Examples: Fez* iron I I ) Ion FeJ iron[lll)'ion cu* copper I ) ion cu2* copperh) 'ion (b) older rule (but st111 used). Latin stem for the element + "ous' for the lesser charge and + 'ic' for the areater charge

- I

Examples:

cuprous ion Cu" cuprlc Ion Sn" stannous ion Sn'* stannic ion

Rule: ?

(Hg2: is mercury(l1) ion, but that IS a monatomic ion.)

I gure 1. Scheme for naming cations.

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I Ne ative Ions 1 I hnions) I i I

I 1 M e : Stem of the element name I + 'ide.'

Examples: H hydride ion F fiuoride ion 02- oxide ion N" nitride ion C+ carbide ion

(Containing Oxygen) Exceptions Containing Hydrogen

less oxygen:

most oxygen: per-ate Ion Examples:

Examples:

C N cyanide ion CiO; chlorite ion

SCN- thiocyanate ion chlorate ion

OCN cyanate ion CiO; perchiorate

peroxide ion SO,'. suifite ion

superoxide ion SO." sulfate ion

We. H - 'oxyanion: 'hydrogen'

+ name of oxyanion or 'bi' + oxyanion

H, - oxyanion: 'dihydrogen' t name of oxvanion

Examples: HCO; hydrogen carbonatc

ion or bicarbonate ion

HSO; hydrogen suifate iol or bisulfate ion

HP04* hydrogen phosphat~ ion or biphosphate ion

H,PO; dihydrogen phos- phate ion

MnO,* manganate ion

two of the four ions rule because it is a compound

Cr,O,& dichmmate ion and not an ion.

Ic-0." oxalate ion 1 I Figure 2. Scheme for naming anions.

Rule: Name of cation + name of anion (word 'ion'

Examples: NaCi sodium chloride MgCI, magnesium chloride Fe,N, iron(il) nitride NaZCOa sodium carbonate NH,OH ammonium hydroxidt NaH sodium hydride CaH, calcium hydride

Comment: The name does not indicatt the numbers of cations and anions because there is oniv one oossibiiiitv for the ion; to combine td form a compound.

I Canpounds I Covalent

(Nonmetal-Nonmetal)

H-Metal H-Nonmetal

Comment: a. These H-containing compounds are named as if thev were ionic

Rule: a. Less eiectronegative element first (exceptions: when one of the elements is hydrogen). b. Number d atoms of each kind specified by GreeE prefixes. c. Prefix (mono) at beginning is dropped

Prefixes: 1 = mom, 6 = hexa 2 = di 7 = hepta 3 = tri 8 = octa 4 = tetra 9 = nona 5 = penta 10 = deca

-

?

? 1

compourids. b. The (aq) in the formulas of the acids is often omitted when it is obvious from the context that they are acids.

I Rule 1: (without the presence of H,O) hydrogen -ide

Exam les HCi lydrkgen chloride HF hydrogen fluoride H,S hydrogen sulfide

Rule 2: (when dissolved in HQ hydro -ic acid

Examples: HCi(aq) hydrochloric acid HF(aq) hydrofiuoric acid H,S(aq) hydrosuifuric acid

-" -...r.- ". HCIO hypochiomus acid HCIO, chiorous acid HCIOs chioric acid HCiO, perchioric acjd HNO. nitrous acld

Rule 1: (without the presence of H,O) like ionic compounds: cation + anion

Hydrogen hypo-ite ~~d~~~~~ -ite tiydrogen -ate Hydrogen per-ate

Rule 2: (when dissolved in H,O)

hypo-ous acid -OUS acid

$Z,"'kid Framnlnr.

H N ~ nitric acid HS03 sulfurous acid H&O, sulfuric acid H,P03 phosphorous acid H,PO, phosphoric acid 1 ~ommenk, The (ad IS usually omitled. I I

N 0. ' dinitrogen tetroxide cb carbon monoxide CO, carbon dioxide NO nitrogen dioxide ~ , d dinitrogen monoxide

Comment: Tetraoxide becwnes tetr- oxide, monooxide becomes monoxide, etc., so that the name sounds better. H-containing compounds do not follow a rule concernino the order in which the-elements are written and shouid be memorized (H,O, NH,, etc.).

gure 3. Scheme for naming compounds.

614 Journal of Chemical Education