Ch9_4_BondProps - Bond Properties 1 2 • What is the...

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Unformatted text preview: Bond Properties 1 2 • What is the effect of bonding and structure on molecular properties? Double bond 3 Bond Order Bond Order Bond Order: # of bonds between a pair of atoms Fractional bond orders occur in molecules Fractional occur with resonance structures. •• •• Consider NO2N N Single bond •• O •• •• • O •• • ••• O ••• •• O •• The N—O bond order = 1.5 Bond order = Acrylonitrile Buckyball in HIV-protease Bond Order Bond Order Bond order is proportional to two important bond properties: (a) bond strength (a) bond (b) bond length Triple bond 4 Total # of e- pairs used for a type of bond Total # of bonds of that type Bond order = 3 e - pairs in N—O bonds 2 N— O bonds 5 6 Bond Length Bond Length Bond Length Bond length depends on size depends size of bonded atoms . • Bond length is the distance between the nuclei of two bonded atoms. 110 pm 123 pm H—F H—Cl 414 kJ 745 kJ Bond distances measured Bond distances measured using CAChe software. In using CAChe software. In Angstrom units where 1 A Angstrom units where 1 A = 10-2 pm. = 10-2 pm m. Page 1 H—I 7 Bond Length Bond length depends on bond depends bond order . 8 9 Bond Strength Bond Strength • —measured by the energy req’d to break a bond. See Table 9.9 • —measured by the energy req’d to break a bond. See Table 9.9. • BOND STRENGTH (kJ/ mol) STRENGTH H—H H—H C—C C—C C=C C=C C≡C 10 Order Length HO—OH 1 142 pm 142 pm O=O 2 121 1.5 128 We’re Done! ? •• •• O O •• •• •• •• O• O• •• • •• • Strength 11 494 •• •• O O 945 The GREATER the number of bonds (bond order) the HIGHER the bond strength and the SHORTER the bond. Bond Strength Bond 835 835 N≡N Bond distances measured Bond distances measured using CAChe software. In using CAChe software. In Angstrom units where 1 A Angstrom units where 1 A = 10-2 pm. = 10-2pm pm. 436 346 602 210 kJ/mol kJ/mol Page 2 ...
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This note was uploaded on 10/19/2011 for the course CHM 2210 taught by Professor Staff during the Spring '08 term at University of Central Florida.

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