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My textbook says that all the bonds of $\ce{SF4} $ are not equal while in the case of $\ce{XeF_2}$, $ \ce{BF4-} $ or $\ce{SiF4} $ all the bonds are equal. No reason is stated for this observation.

So is there a general way or formula to check if all the bond lengths are equal or not for a given molecule?

Melanie Shebel
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Abhishek Mhatre
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    Please use the mhchem package for $\LaTeX$ formatting. Chemical formulas and equations mustn't be slanted. – M.A.R. Aug 12 '15 at 15:06
  • You have to check geometry of the molecule – Mithoron Aug 12 '15 at 15:07
  • So the geometry will be trigonal bypyramidal, trigonal bypyramidal, square planar and square planar for $\ce{SF4} $, $\ce{XeF_2}$, $ \ce{BF4-} $ and $\ce{SiF4} $, respectively. What should I do next? – Abhishek Mhatre Aug 12 '15 at 15:27
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    Where in this question comes the valence bond theory into play? Currently it reads more like a question about the simple predictions of the VSEPR model, geometries of certain molecules. It does not seem to be at all about VBT. Maybe some other tags and a more descriptive title would help this question. – Martin - マーチン Aug 12 '15 at 18:03
  • 4 times wrong, sorry but without knowing VSEPR case is bad. http://chemistry.stackexchange.com/questions/18427/why-f-replaces-axial-bond-in-pcl%e2%82%85 may help – Mithoron Aug 12 '15 at 18:04
  • Did you mean the the shape of the molecules or the geometry of the molecules? The VSEPR of the molecules will be 5(4 bond pair, 1 lone pair), 6 (4 bond pair, 2 lone pair), 4(4 bond pair, 0 lone pair) and 4 ( 4 bond pair, 0 lone pair) for $\ce{SF4}$ , $\ce{XeF_2}$, $ \ce{BF4-} $ and $\ce{SiF4}$ ,respectively. I asked my teacher and he said that the molecule with VSEPR 3 or 5 has to be the answer. So the answer has to be $\ce{SF4} $ – Abhishek Mhatre Aug 13 '15 at 14:30

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