Lewis Structures of Oxygen Compounds of 3p-5p Nonmetals Dare1 K. Straub University of Pittsburgh, Pittsburgh, PA 15260
The treatment accorded Lewis structures of compounds of the 3 p 5 p nonmetals (P, As, S, Se, Te, C1, Br, I, Xe) in many college general-chemistrr textbooks is confusing, and &atisfaciory in some respects, mainly due to the attempt to enforce the octet rule upon these compounds as the normal or best descri~tionof the bondine. Alone with these octet structures, structures involving "expanded octets" are usually shown, necessitating a variety of mesomeric and resonance forms. (For example, for ~ 0 4 %there can be as manv as 11forms. involving no. one. or two double bonds.) ~ o b e v e rin , many (but n i t ail) cakes the octet structures are either tacitlv or exolicitlv assumed to be the single best representations of the actual structures. In this DaDer I ~ o i n out t that if it is assumed that the octet ruleapplies'only to the 2p, and not the 3 p 5 p elements, good Lewis structures of oxides, oxoacids, and oxoanions can be easily written using the very simple procedure given below. Two recent articles in this Journal by Carroll ( I ) and Purser (2), also emphasize the unimportance of the octet rule in SOz, SOa, HS04-, and related structures.
-
-
Discussion When the expanded octet for P to Xe in their oxides and related compounds is no longer considered unusual or somehow undesirable, but is taken as the norm, attention may then be focused on the bonds of these elements with oxygen. Oxygen can bind to nonmetals in four ways.
uncommon and occurring essentially only with the 2p elements, as in CO or NOt
Table 1. Bond Lengths (A) in Oxoacids of 3p-5p Nonmetals
Oxoacida
HO-X
X-O(termina1)
Ref
H~PO~S) HzSOa(g) HzS04(s) HnSeOds) HsTeOds) HCIO(S) HClO4(g)
1.499-1.555 b 1.574(10) 1.422(10) c 1.535(15) 1.426(15) d 1.739(6) 1.655(6) e f 1.916(2) 1.691(1) 9 h 1.635(5) 1.408(2) HBW) 1.834(1) i 'Abbreviations: g, gaseous state; s,solid state Exlens ve nyarogon bondmg in sol o Tne I 499 va1.e sine werageof P 4 shone, oonds an0 me 1 555 !he average of P4langsr oonos in severa corn ~omm Conla n na- HIPOI Blessma -. R rl Acta Crvst 1988. 844. 334-340 E K ~ ~ ~ k oR.~L.;~ Suenram, k i , R. 0.; Lovas, F. J. J. Am. Chem. Sm. 1981, 103.2561-2566. d~ascard-~illy, C. Acfa Cwt. 1965, 18.827429. 'Average 01 IWO cases (both involve hydrogen bonding): Larsen, F K.: Lehmann. M. S.; Setone, I. Acta. Chem. Scand. 1971. 25,1233-1240:Baran, J.; Lis, T : Marchewka,M.; Ratajczak, H. J Mol Stmct 1991,250,13-45. '~verageof six cases: Averbuch-Pouchot, M. T. J. So1;dState Chem. 1983, 49, 368378: Ilczyszyn,M. M.; Lis. T.; Baran, J.; Ratajcrak, H. J Mol. Struct. 1992,265,293-310; Averbuch-Pauchot, M. T. Durif, A. Act8 Ciyst. 1992, C48, 973-975;Averbuch-Pouchot, M. T.; Durif. A. Ada Ciyst. 1991. C47.157679. oAndenon,W 0.; Gerry. Mc. L.: Davis, R. W. J. Mol Sp~ctmsc.1986, 115, 117-130. h a r k , A. H.; Beagley, B.;Cruickshank,D. W. J.; Hewitt,T.G. J. Chem. Soc A 1970.1613-1616. 'Kaga. Y ; Takea. H.; Kondo, S.; Sugie, M.; Matsumura, C.; McRae, G. A ; Cohen, E. A. J. Mol. Spectrosc. 1989, 138,467-481. with all terminal oxygen atoms doubly bonded. Measured Bond Lengths
as terminally bonding
This simplified picture is remarkably effective in predicting relative bond lengths, even for anions having several resonance forms. Some of the recent and most accurate data on measured bond lengths of several oxides, as the bridging form mixed oxides, oxoacids, and oxoanions of the 3 p 5 p non-0:. metals, together with predicted bond orders, are given in as the ionic form Tables 1-5. Error limits are indicated in parentheses; when several structures are averaged, the limits are estiThese forms give the least possible formal change to the mated. (Hydrogen bonding in solid oxoacids and prooxygen and to the central nonmetal atom. tonated oxoanions reduces the difference between the preAfifth possible form, dicted single- and double-bond forms (3)). =OH+ It is rather surprising andvery gratifying that the measured bond lengths correspond so closely to those suggested in which the -OH group acts as a n base, only occurs when by these simplest Lewis structures, with little or no overthe atom to which the -OH group is bonded would otherlap in the range of usual bond lengths for each predicted wise lack an octet of electrons, and is thus essentially limbond order. Take the C1-0 bond as an example. For ClOz+, ited to boron compounds, for example, B(OH13. C104, C103-, ClOz-, and C10-, with predicted bond orders Possible mesomeric forms of Lewis structures in this of 2, 1.75,1.67, 1.50, and 1,the average C1-0 bond lengths view are not considered important in describing the bondare 1.39 1.43 1.49 A, 1.58 and 1.67 Based upon ing. Thus, for example, such structures would be written, the data in these tables, sin le and double-bond lengths are shown in Table 6 6: 0: 6: 0: 0: I 11 I 11 .. B - 1 : H-&CI=O: :O=Xe=O: 0 :0=I-WI=0: .. .. .. Bond Shortening .. 1, 0: 0: :0: Terminal oxygen is written with a double bond, (4 resonance forms) even to the heavier 5p elements iodine and xenon.
.
.. ..
..
A,
..
..
..
..
A,
A.
(I)..
Volume 72 Number 10 October 1995
889
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Table 2. Bond Lengths (A) in Oxoanions of Phosphorus, ~rgenic,'sulfur, Selenium, and Tellurium
Ion
Number of Resonance Forms
POb
Predicted Bond Order
X-O Bond Length
POSF"
4 3
1.25 1.33
1.542(5) 1.509(4)
POzFz ~s04*
2 4
1.50
1.469(12)
~03'-
3 6
1.25 1.33 1.50
1.682(6) 1.530(6) 1.468(6)
-
Table 3. Bond Lengths (8) . , in Halogen Oxoanlons
Ref
a
b b
Anion Numberofpredicted CI-O Ref Resonance Bond Forms Order 1 1.00 1.673(8) a XOX022 1.50 1.577(2) b XOC 3 1.67 1.486(2) c X044 1.80 1.427(5) d X02+
1
c
2.00
1.391(4)
Br-O
Ref
I d
R~ef
1.814(9)
a e
1.929(10)
a
f g
1.809(2)
h
1.775(7)
i
1.716(2) 1.659(2) 1.605(3)
-
j
'Gilles, M. K.; Polak, M. L.: Lineberger, W. C. J. Chem. Phys. 1992, 96,8012-8020. '~verageof three cases: Marsh, R. E. ~ c t cryst. a 1991, ~ 4 7 1775; , Okuda, M.; Ishi~04'e h a m M.: Yamanaka, M.; Ohba, S.; Saito, Y. Acta C w t 1990. C46. 1755-1759. Averageaf sixcases: Lutz. H. D.; Alici, E.; Buchmeier, W. 2.Anorg. Altg. Chem. 1986, S~O? 3 1.33 1'697(8) . ; 5 3 1 4 8 ; Gallucci. J. C.; Gehin, R. E. Acts Cryst. 1990, C46.350-354: Blackburn, A. 6 1.50 1.641(2) 2 ' C ; Gallucci, J. C.: Gerkin, R. E. Acta Cryst. 1991, 847,474479. Te0? 3 1.33 1.854(5) h d~verageof tive cases: Escobar, C.; Winke, 0. Acta Cryst. 1983, C39, 1643-1646; T~O? 1 1.00 1.941(5) i Gallucci, J. 6.; Gehin, R. E. Acta Cryst 1988, C44, 1873-1876; Gallucci, J, C.; Gerkin, R. E. Acta Cryst. 1989. C45, 1279-1284. 'Corbridge, D. E. C. Topics PhosphorusChem. 1966.3.57-394. 'Levason, W.; Ogden, J. S.: Spice,, M. D.: Websfer, M.; Young, N. A. J. Am. Chem Soc '~verage of three cases: Bemdt, A. F.; Sylvester. J. M. Acta C w t 1989, 111,621&6212. 1972, 828,21914193. '~verageof five cases: Lutz, H. D.; Alici, E.; Buchmeier. W.; 2.AnorgAllg. Chem 1986, 'Averageof seveal cases: van der Veken. J.: Vansant. F. K.: Henan, 535.31-38; Blackburn, A. C.; Gallucci, J. C.; Gerkin, R. E. Acta Cryst 1990, 846,712M. A. J M o l Stmd. 1977.36.225-232: Boubia. M.; Averbuch-Pouchot, 716: Blackbum, A. C.; Gallucci, J. C.; Gehin, R. E. Acta Cryst 1991, C47.17861789. M. T.; Durif. A. Acta Cryst. 1985. C41, 1562-64. gAverage of fourcases: Blackburn. A. C.; Gallucci, J. C.; Gehin, R. E.; Reppart, W. J. d ~ ~ ~ r of a three g e cases: Bats, J. w.; Fuess, H.; Elerman, Y. Ada ~ c t cryst. a 1992, ~ 4 8 . 4 1 ~ 2 4 . cryst. 1986. 842, 552-557; Andenon, L.: Langer, V.; Stramberg, A.; Qverage of eight cases: svensson, c.; Albertssan, J.: Liminga, R.; Kvick. A,; AbraStromberg, D. Acta Cryst. 1989,845,344348, hams, S. C. J. Chem. Phys. 1983, 78.7343-7352: Crener, J-M.; Coquet. E.; Pannetier, 'Average oflhreecases: Cole, W. F.: Lancucki, C. J. Acfa C w f . 1974. J.; Bouillot, J.; ~ u r a n d - L ~ F I O C M.~J, SolidState Chem. 1985,56133-147: ~ u t zH. , D.; 830, 921-929; Galesic, N.; Jordanovska. V. B. A m Cyst. 1992, C48, Alici, E.; Buchmeier, W. Z Anorg. Allg Chem. 1986,535,31-38; SenGupta, P K.; ~ m m o n , 25y258. H. L.; Abrahams, S. C. Acta Cryst 1989, C45, 17S178; Lutr. H. D. Kellersohn, T.; Vagt, Average of two cases: Andenen, L.; Langer, V.; Stkimberg, A.; StrilmT. Acta Cryst. 1990, C46.979-981. berg, D. Acta C w t 1989,845,344348, 'K~lmAn.A ; Cruickshank, D. W. J. A d a Cryst. 1970. B26, 1782-1785. of five cases: KA1mBn, Stevens, J. '.; CNickshank~ D. W. '~verageof three cases: Mallouk, T E.; Desbat, 5.: Baltlen. N. hlorg Chem. 1984.23, J.ActaCWst1970, B26, 1451-1454: Prevost-Czeskleba, H.; H. 3160-3166: Mallouk, T. E.: Rasenthal, G. L.; MOller, G.; Bwsasca, R.; Banlen, N. tnorg. Takahaski, I ; Onodera, A.; Cryst. 19=, C40. Y. Chem. 1984, 23, 3167-3173; Bougan. R.; Cicha, W. V; Lance, M.; Meublat, L.: Nierlich, Acta Cryst.1987. C43.179-182: Baran, J.; Lis,T; Marchewka, M.: Rata- M.; vigner, J. lnorg. them. 1991, 102~109, jczak; H. J. M o i Shuct 1991, 250, 13-45: Kr"ger, R-R.; Abriel, W. Acta Cryst. 1991. C47.1958-59. (5)).Certainly for the 3p and 4p nonmetals there is very h~verage of five cases: Anderson. L.; Langer, V; Strtimberg. A,; Stkimberg, good evidence, both experimental and theoretical, for true D. Acta cryst. 1989. 845, 344-348. double-bond formation with terminal oxygen, for example, ' ~ v e r a of ~ etwo cases: it, B.; ROUI~,G.; G ~ I YJ., J. sotid state them. 1983, 48. 246-255. P=O (61, As=O (7), S=0 (81, Se=O (9),C1=0 (10). Toscano
d
S~OP
While the magnitude of n-bonding in these cases may he in dispute, the terminal-oxygen bond lengths are consistently significantly shorter (sometimes by as much as 0.3 A) than the bonds involving bridging oxygen or the ionic form
..
-0: .. -
That such shortening cannot be ascribed completely to ionic contributions to single bond lengths (i.e., to M(+)-0" vs. M=O)is evident through use of the SchomakerStevenson correction to the AB single-bond length, that is, - 0 . 0 7 ( ~-~XB)' A (4). Differences between the single-bond and assumed double-bond lengths given above, and the Schomaker-Stevenson corrections using Pauling electronegativities, are in A,
..
PO, 0.15,O.ll
SO, 0.17, 0.05 SeO, O.11,0.06 C10, 0.26; 0.005 BrO, 0.25,0.02
and Russo demonstrated that even triple-bond formation can occur with the 3p and 4p nonmetals for all diatomic (gaseous state) combinations of nitrogen, phosphorous, arsenic, and antimony, including Sb-Sb (11). Discussion of the vexing question of d-orbital participation in bonding in a hybridized atomic orbital (12)is best omitted a t the general-chemistry level because students normally have considerable difficulty in writing Lewis structures as it is. The raison d'@treof these simplifiedLewis structures then resides mainly in their pheuomenologid importance in predicting and describingqualitativelyparameters such as relative bond lengths, bond strengths, possible barriers to rotation about bonds, and other details of molecular structure, in the simplest possible way Conclusions The relatively common practice in general-chemistry textbooks of showing several mesomeric forms for the oxides, oxoacids, and oxoanions of the 2 p 5 p nonmetals, such as
:0: I
10, 0.31, 0.08
XeO, 0.32
H
In all cases the M(+)-0" formulation for terminal oxygen predicts longer bonds than are actually found; with the more electronegative elements (sulfur and the halogensb, the corrections shorten the single-bond lengths by 0.05 A or less. The only case that is somewhat ambiguous involves the PO bond, where the ionic form may account for perham 80% of the decrease in bond leneth in eoinrr from bridged oxygen to terminal oxygen. (However, there is considerable controversy in the literature over the PO bond
-
890
Journal of Chemical Education
-
I :0:
0: I1 H
0 $0
0: H-+o:
:0
0:
H-&#+a: 0:
(3 resonance forms) (6 resonance forms)
for perchloric acid leads to predictions of bond lengths that agree less with the measured values than do the lengths from structures based entirely upon the divalency of covalently bonded oxygen. Thus, nothing is gained in such elaboration (though it may he suitable for an advanced treatment of bonding in an upper level course). Much is
Table 4. Bond Lengths (A) in Oxides and Mixed Oxides of Phosphorus, Arsenic, Sulfur, Selenium, and Tellurium Compounda
X-O(bridging)
P4010(g) POh(g) FzPOPFz(g)
X-O(terminal)
Ref
1.604(3)
1.429(4)
-
1.437(4)
b c
c120(g) CH30CI(g)
d
C1207(g) FCIOz(g)
1.631(10)
-
(CH3)3PO(g) (CHs0)3PO(g) (CH~)~ASO(~) S02(9) so3(g) sOFz(g) SOzFz(g)
Table 5. Bond Lengths (A) in Oxides and Mixed Oxides of Chlorine, Bromine, Iodine, and Xenon
-
1.580(2)
1.476(2) 1.477(6)
-
1.631 (3) 1.432(2)
-
1.418(1)
-
1.421(3) 1.405(3)
Compounda
X-O(bridging)
X-O(terminal)
Ref
1.693(3)
-
b
1.41 6 1.420(3)
d e
1.674(19) 1.723
-
1.400(2)
f
1.405(3)
9
(C6H5)3SiOC103(~)
1.535(5)
1.368(8)
h
BrzO(s)
1.85(1)
-
9 i
BrzO4(s) FBrOdg)
1.86(2)
e
f e
FCIOdg)
9
h
hClO(g)
IOFS(S) 1204F6(S)
1.939(7)
1.744(8)
I(OTeFs)4-(s) CII(OTeFa)+)
2.117(9) 2.076(5)
-
1.621 (7)
-
I
(CH30)zSOz(g)
1.567(3)
1.41 9(4) 1.438(3)
k I
1.607(1)
m
1.688(1) 1.576(3)
n 9
XeWg) XeOFdg)
-
o o
XeOzFz(g) XeOF3+(s)
-
P
FXeOSOzF(s)
P P
HF.HOTeF40Xef(s)
2.155(8) 1.962(9)
Xe(OTeFs)n(s)
2.032(5)
-
SeOz(g) SeWg) SeOFdg) (FsSe)eO(g)
1.697(13)
(FsTe)zo(g) CII(OTeFs)n(s)
1.832(12) 1.833(5)
I(OTeFd4-(s) OI(OTeFs)4-(s)
1.826(10) 1.831 (6)
Xe(OTeFs)4(s)
1.885(5)
q
OzXe(OTeF5k(s) 1.860(5) q 'Abbreviations: u, uaseaus slate; s, solid state. b~eagley, 6.; ~ ~ i c k s h a nD. k .W. J.: Hewin. T. G.; Haaland, A. Tnns Fanday Soc. 1967.6.3.836845. 'Kagann, R. H.: Ozier, L.: Gerry. McL. J. Mol. Spectmsc. 1978, 71, 281-298. d ~ oH.;~ Rudolph, , R. W.; Bartell, L. S. J. Mol. Strun 1975, 28, 200Fr215. Wilkins, C. J.; Hagen, K.; Hedberg, L.; Shen. Q.; Hedberg, K. J.Am. Chem. Soc. 1975.97.6352-6358. '~berharnmer,H I Naturfosch. 1 9 n . 2 8 ~ .114M144. gGregaly, D.; Harginai, L.; Kolonits, M. J. Mol. Stmct. 1976, 31, 261-267. "eyer, V: Suiier, D. H.; Dreizler, H. Z.~aturfosch.1991. 46A, 71&714. '~ide,Jr, D. R.; Mann, D. E.: F.strom, R. M. J. Chem Phys 1%7,26,734-739. i~uschmann.J.: Luger. P.; Karitsanszky, T.; Schmidt, H.; Steudel. R. J Phys. Chem. 1992,96,9243-9250. *BN~VOII, J.; Exner, 0.; Harginai, I. J. Mol. Slruct 1981, 73, 9%104. '~verageof five different salts: Jannin, M.; Puget, R.; deBrauer, C.: Perret, R. Acta Ciyst. 1991, 127, 1687-1689; Jannin, M.; Puget, R.: deBrauer, C.; Perrot, R. Ada Cyst. 1991, C47,2228-2229; deBrauer, C.; Jannin. M.; Puget, R.; Perret, R. Acta Cwsf. 1991. C47.2231-2232; Jannin, M.; Puget, R.; deBrauer, C.: Perret. R. Acta Cryst. 1993. C49,749-751. "'Takeo, H.; Hirota, E.: Morino, Y. J. M o l Speclmsc 1970, 34, 370382. "Brassington. N. J.; Edwards. H. G. M.; Fawcen. V Speamchim. Acla 1987, 43A. 451-454. 'Ooernarnmer, H Seppen. 6 h o g Chem 1978. 18. m€-222% q.nfiusny L.; Seppelt K. L Anorg. Allg. Chem 1991. 602 79-87 '?.rawsky L , Soppdt K. z ~ n o Alrg g Cnern 1992.609 153-156.
.
i
1.61(2) 1.582(1) 1.715(4)
(CH30)zS(s) (CH3)3SO+(s)
c
-
I k I
m n n
1.736(2) 1.703(2)
o
1.714(4)
P
1.692(13)
P
-
q
-
s
P
r
OzXe(OTeF5)z(s) s 2.022(5) 1.729(5) 'Abbreviations: g, gaseous state; s, solid state. %agley, 8.; Clark. A. H.; Hewin, T G. J Chem. Soc. 19681,658462, 'Rigden, J. S.; Butcher. S. S. J. Chem. Phys. 1964. 40,2109-2114. d~imon, A.; Bomnann, H. ~ n g e w Chem. ~ n~ t d~ .n g1988,27,1339-1341. ~. 'Robiene, A. G.; Parent, C. R.: Gerry, Mc. L. J M o l Speclrosc. 1981, 86, 45y64. Burczyk, K.; Burger, H.; LeGuennec. M.: Wiodarcrak, G.; Demaison, J. J. MoI Spectrosc. 1991. 148.65-79. OOberhammer,H.; Christe, K. 0. ~norg.chem. 1982.21. ~ 7 ~ 2 7 5 . "rekash, G. K. S.: Keyaniyan, S.; Aniszfeld. R.: Heiliger. L.; Olah, G. A.; Stevens, R. C.: Chai, H-K.; Bau, R, J. Am. Chem. Soc. 1987, 109,51235126. 'Levason. W ; Ogden, J. S.; Spicer, M. D.; Young, N. A. J. Am. Chem. Soc. 1990. 112.101%1022. i ~ i b ~Tn R.; . Levasan, W; Ogden. J. S.; Spicer, M. D.; Young, N. A. J.Am. Chem. Soc. 1992. 114.546%5470. *~ppelman,E. H.; Beagley, 6.: Cruickshank, D. W. J.: Food, A,: Rustad. S.; Ulbrecht, V. J. Mol. Struct. 1976. 35.139-148. 'Bartell, L. S.; Clippard, F B.: Jamb, E. J. Inorg. Chem. 1976, 15,30O(M013. mSrnan.L. E. J. Chem. Soc., Chem. Comm. 1977 519-520. "Turowsky, L.; Seppelt, K. Z Anorg. Allg. Chem. 1991, 602, 79-87. 'Gundewan, G.; Hedberg. K.; Huston,J. L. J Chem Phys 1970.52.812-815. PMer~ier,H. P. A.; Sanders, J. C. P.; Schrabilgen, G. J.; Tsai. S. S. Inorg. Chem. 1993,32,38+?-393. qBartien, N.; Wechsberg, M.; Jones. G. R.: Burbank, R. D. /nor@ Chem. 1972.. 11.. 1124-1127. %rowsky, L.; Seppeii. K. h o g . Chem. 1990.29,32263228. =Turowsky, L.; Seppelt, K. 2.Anog. Allg. Chem. 1992,609,15>156
l o s t in c l a r i t y , e a s e o f u n d e r s t a n d i n g and writing L e w i s s t r u c t u r e s , and closeness t o actual s t r u c t u r e s .
Table 6. Average Bond Lengths
Literature Cited 1. C a m l , J.A J Cham. Edue. 1988,63,2631. 2 Purser, G.H. J. Cham. Educ. 1983.66.710-113 3. Fernaria, 0.; I d & , G.Arto Cvst 1984, B40, 1-6.
X=
X-0 (in A)
X=O (in A)
4. Porterfleld,W. W. InorgonieChamisfmA UdfmdAppmach;Addison-Wwwley:Reading, MA, 19% p 167. 5. hjca, A ;Rice, J. E.; Streitweiser, Jr.,A.;Sehaefer llI, H.F J Am. C h . Soc 1987, 109, 41894192 Rebuttal: Horn, H.; Ahhchs, R. J Am. Cham. S a 1990, 112, 7171.7174 . .. .. . ... 6. Baraniak,J.; Frey, P A . J h Cham. Sor 1988,1ID,405%4060:Un,S.;Klein,M.P, J.Am. C h . Soc 1889,111,511~5124. 7. van der Veken, J.;Vanssnt, l? K.; Herman, M. A. J.Mol. S h u c t 1817,36,225-232; seppea, K&W cham ~ n t~. dEngl.1970,15,766767. . 8. wang,x: G"0.L. w: Li", H. c.; Kao, C. T.;Tsai, C. J.; Bat=,J. W I w r g Cham. 1888, Xe 2.04 1.72 (The SeO, bond length of 1.688 A, Table 4, was not determined by the more direct method of electron diffraction but was derived from Raman data. It appeas exceptionally long.)
Volume 72 Number 10 October 1995
891
