Bond Energy Data Summarized Nicholas K. Kildahl Worcester Polytechnic Institute, Worcester, MA 01609

Bond energies are so important in discussions of inor- ganic reactivity that a useful and reasonably comprehen- sive 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 ta- ble format show the trends, but rarely present energies of more than one type of bond (e.g., strengths of single self- bonds 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 rational- ize chemical behavior. As an assistance to both myself and students. I develo~ed the ~eriodic table bond enerm sum- -- mars 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

" A

be the first to admit that I present neither new data nor

Selected Bond Enersieo (LJlnale)

new format. However, I believe that this particular presen- tation 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-bond energies of the element; . the energy of the element-hydrogen bond; the energies of the single and double bonds of the element to oxygen; and tinally, the energy of the element-fluorine single bond.

Bond energies not specifically listed in the figure can be estimated readily from the I'nuling equation r~ncluded in the figure uudcr ihe Kcy box, and the electnmrjiativities.

KEV I - I 1A.x IEl-nt ~ynb l ,E lec t rmega t i v i r y 10.2.04 IC.2.55 IN.3.04 10.3.44 1F.3.98 IYe

1293 1346 1167 1142 (155 1 I - - - 1602.8351418.9421194 I--- I 1385 1411 1386 1459 1565 1 ~536.636~358.lW~201,607~142,494~--- 1 1613 I485 1283 I190 1155 1 I ~A1.1.61~Si,l.9O~P,2.19 16.2.58 IcL.3.161Ar I--- 1222 1-220 1240 I240 I I--- 1318 1---,4811425 I--- I I272 1318 1322 1363 1428 1 I - - - 1452.6C01335.5441---.123~218 1 1583 1565 1490 2 8 4 1249 (

I ~Ea.l.81~~e.2.Ol~As.2.18~Ee.2.55~Br.2.96~Kr.3. 1 1113 118(1 1146 1172 1190 I I I--- 1272 1---,3801272 I--- I I I--- I - - - 1247 1276 1362 1 I I--- I--- 1301,3891--- 1201 I 1 1469 1470 1'440 11.351 1250 1 50

-I---+'- ~1n.1.78~sn.1.80~Sb.2.05~1e.2.10~1.2.66 Ixc.2. 1100 1146 (121 1126 1149 I I - - - I--- 1---,295I218 I--- I . . . . . . . . . ~ 238 1295 I . . . . . . ~ . _ _ ~ _ _ _ 1201 1 84

1~523 11.150 2 15393 1278 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___ 1.. I... I

I I 1 . . I _ _ _ I _ _ _ I I I

1439 1-360 1=350 1 I I 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 peri- odi three through-six; however, the unusually weak single self-bonds of the period two elements in these groups, at- tributed to interatomic lone-pair repulsions at short dis- tance, are clear.

Groups 14-16 show a steady decrease in multiple self- bond 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 in- creases. A sharp decrease at N that persists through F again shows the interatomic lone-pair repulsion effect. Pe- riods three through five continue this trend: A smooth in- crease 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.

In e r o u ~ s 15 and 16. the ~ e r i o d two elements form dou- , A

ble silf-bonds that are more than twice as strong as their sinele self-bonds. due to a laree reduction in interatomic l ~ n i - ~ a i r repulsibns when hybGdization changes from sp3

'Several of these examples were suggested by my colleague, Ladislav H. Berka.

to sp2. In all other cases, double bond energies are less than twice the corresponding single bond energies.

Using this presentation of bond energy data, one can ex- plain 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 in-

volves SS bonds; 8. acidity of the binary hydrides of groups 16 and 17 in-

creases down the group; 9. boron hydrides spontaneously ignite in air;

10. expected "hydroxides" (i.e., oxoacids) of period two ele- ments are unstable (ex.. C(OHL decornooses to H.420.: ", N(OH), decomposes to NO^ (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 Si- 0 bonds:

14. s11mn forms n lmitcd scncs of'catrnawd ailanes; and I5 thr chemistry ofcorbun is extenswe.

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 as 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~tW W. 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.

424 Journal of Chemical Education