Bond Energy Data Summarized Nicholas K. Kildahl Worcester Polytechnic Institute, Worcester, MA 01609 Bond energies are so important in discussions of inorganic reactivity that a useful and reasonably comprehensive summary of available data is invaluable. The tabular presentationused inmost inorganic texts (e.g., 1-31 fails to clearly reveal periodic trends. Presentations in periodic table format show the trends, but rarely present energies of more than one type of bond (e.g., strengths of single selfbonds of the elements). (. I.) .For several vears. I have taueht a third-year course in main group. inorganic chemistry in which I rely heavily on bond energy arguments to rationalize chemical behavior. As an assistance to both myself and students. I develo~edthe ~eriodictable bond enerm -- summars shown in the iimrk. I t combines in one page the quick visual summaryof periodic trends and theplethora of data contained in a tmical tabular resent at ion. I will be the first to admit that I present neither new data nor
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" A
new format. However, I believe that this particular presentation will be useful to many of my inorganic colleagues, and I offer it in that spirit. The box a t top center of the figure provides a "Key" to reading the data. To the right of the symbol for the element (Ais used as a generic symbol in the Key box) is its Pauling electronegativity. Under the element symbol are listed t h e single self-bond energy of the element; the double and triple self-bondenergies of the element; the energy of the element-hydrogenbond; the energies of the single and double bonds of the element to oxygen; and tinally, the energy of the element-fluorinesingle bond.
.
Bond energies not specifically listed in the figure can be estimated readily from the I'nuling equation r~ncludedin the figure uudcr ihe Kcy box, and the electnmrjiativities.
Selected Bond Enersieo (LJlnale)
-
I
KEV
1A.x
IEl-nt
I
~ynbl,Electrmegativiry
10.2.04 1293
IC.2.55 IN.3.04 10.3.44 1346 1167 1142 1602.8351418.9421194 1411 1386 1459
1F.3.98 (155
IYe
1 I 1385 1565 1 ~536.636~358.lW~201,607~142,494~--1 1613 I485 1283 I190 1155 1 I I---
~A1.1.61~Si,l.9O~P,2.19 16.2.58 1222 1-220 1240 I--- 1318 1---,4811425 I272 1318 1322 1363
I---
I 1 I I I 1
I---
IcL.3.161Ar I240 I
I---
I--- I 1428 1 1452.6C01335.5441---.123~218 1
1583
1565
1490
284
1249
(
~Ea.l.81~~e.2.Ol~As.2.18~Ee.2.55~Br.2.96~Kr.3. 1113
118(1
I--- 1272 I--- I--I--- I--1469
1470
1146 1172 1---,3801272 1247 1276 1301,3891--1'440 11.351
1190
I--1362 1201 1250
I I 1 I 1 50
- ' +- - - I -
~1n.1.78~sn.1.80~Sb.2.05~1e.2.10~1.2.66
Ixc.2.
I I--- I . . . . . 1295 I . . . . . . ~ . _ _1201 ~ _ 1 84_ _ 1100
1146
I---
I---
1 ~ 5 2 3 11.150
(121 1126 1---,295I218 . . . . 238 ~
1149
2
1278
15393
1-131
I ~1l.2.04~Pb,2.33~Bi,2.02~P~,2.00~At,2.20~Rn 1.. . . I.. I 1116 1 I - - - I--- 1---.I921 I I I___ 1.. I. I I I 1.. I___ I___ I I I 1439 1-360 1=350 1 I I Apresentation of homo- and heteronuclear bond energy data, based on the periodic table Volume 72 Number 5 May 1995
423
This single-page presentation contains information, either explicitlv or imolicitlv. -. for discussion of a wide range - of chemical reactions. Periodic trends in bond energies are all readily seen in the figure. The Most Important Main Group Trends Groups one and 14 show the steady decrease in single self-bond energies with increasing atohic size and overiap capabilities. Groups 15 to 17 show the same trend in periodi three through-six; however, the unusually weak single self-bonds of the period two elements in these groups, attributed to interatomic lone-pair repulsions a t short distance, are clear. Groups 14-16 show a steady decrease in multiple selfbond strength down the group. I t is clear that the period two element forms bv far the stroneest double and triple self-bonds. subsequent elements i n these families shbw substantiallv weaker multiple self-bonds. I n period two, single self-bonds become smoothly stronger from Li to C, a s effective nuclear charge increases. A sharp decrease a t N that persists through F again shows the interatomic lone-pair repulsion effect. Periods three through five continue t h i s trend: A smooth increase in single self-bond energy through group 14, a ‘Sag" between groups 14 and 15, and again a smooth increase from group 15 to group 17. I n e r o u ~ s15 and 16., the ~ e r i o dtwo elements form double silf-bonds that are more than twice a s strong as their sinele self-bonds. due to a laree reduction in interatomic l ~ n i - ~ arepulsibns ir when hybGdization changes from sp3 A
'Several of these examples were suggested by my colleague, Ladislav H. Berka.
424
Journal of Chemical Education
to sp2. I n all other cases, double bond energies are less than twice the corresponding single bond energies. Using this presentation of bond energy data, one can explain with little more than a glance why, for example,' 1. HF etches elass:. 2. most explosives involve single bonds between nitrogen and itself or same other element: 3. elemental nitrogen is so unreactive; 4. fluorine is so reactive toward almost all other elements, 5. halogens are unreactive toward oxygen, which reacts readily with most other elements; 6. ozone is unstable with respect to dioxygen; 7. the stable allotrope of oxygen is 0=0, while that of S involves SS bonds; 8. acidity of the binary hydrides of groups 16 and 17 increases down the group; 9. boron hydrides spontaneouslyignite in air; 10. expected "hydroxides" (i.e., oxoacids) of period two elements are unstable (ex.. C(OHL decornooses to H.420.:", N(OH), decomposesto (4; 11. phosphorous acid has the structure P(H)f=O)fOH)2, rather than PfOH),; 12. borates and silicates are so abundant in nature; 13. the stable oxide of carbon is monomeric O=C=O,whereas, that of silicon is the polymeric SiOz,containing single Si0 bonds: 14. s11mnforms n lmitcd scncs of'catrnawdailanes;and I5 thr chemistry ofcorbun is extenswe.
NO^
Although most of the data in the fieure were taken from reference>, the source ofdata is not c';lricnl. The fiaure ran he updated readily a s new data become available. Literature Cited 1. Bowser, J. R. Inorganic Ckemktry; BrookdCole Publishing Pacific Grove, CA, 1993. 2. Sh"ver D. F;Atkins, P. W.; Langford, C. H.Inor#.,nie Ckrni~tWW. H. Freeman and
Company: New York, 1990.
3. Huheey, J. E.; Keiter. E. A,Keiter. R. I- InoganicChemkl'y-Principles ofSlmcfum and Reoefiuily, 4th ed., Harper Collins College Publishers: New York. 1993. 4. Kildahl, N. K J Chem. Educ. 1881,68,1001.
