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2000
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Research: Science and Education
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Should Gaseous BF3 and SiF4 Be Described as Ionic Compounds?
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Arne Haaland, Trygve Helgaker, Kenneth Ruud, and D. J. Shorokhov
Department of Chemistry, University of Oslo, PB 1033 Blindern, N-0315 Oslo, Norway
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August 2000
Vol. 77 No. 8
p. 1076
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| Abstract |
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The atomic charges in BF3 calculated by the "atoms in molecules" approach
are +2.58 and -0.87
for B and F, respectively; in SiF4 the calculated charges are +3.42 and -0.86,
and it has
therefore been suggested that these molecules should be described as fully ionic (R. J.
Gillespie, J. Chem. Educ. 1998, 75, 923). However, atomic charges
calculated by an alternative
approach (from the atomic polar tensors) are lower by more than 30%. Calculations based on a
spherical ion model show that this model underestimates the mean bond energies of BF3
and SiF4
by more than 40%, and calculations based on a polarizable ion model indicate that the
F- ions
are considerably distorted in the direction of polar covalency. It is concluded, therefore,
that a description in terms of a completely ionic model may be misleading.
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| More Information |
 Citation |
Haaland, Arne; Helgaker, Trygve; Ruud, Kenneth; Shorokhov, D. J. J. Chem. Educ. 2000 77 1076.
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Keywords |
Inorganic Chemistry; Bonding Theory; Molecular Properties / Structure
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History |
Created:
Last Updated: |
July 5, 2000
April 15, 2005
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