# Comparing bond lengths of a molecule using valence bond theory?

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?

• 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
• 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. chemistry.stackexchange.com/questions/18427/… may help – Mithoron Aug 12 '15 at 18:04
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