Here it is
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SF₄ ^- has four bond pairs and one lone pair so it has distorted Trigonal bipyramidal geometry which is called as see saw or distorted tetrahedral.Now lone pairs in this shape are present on equitorial which causes more repulsion to axial bonds .Axial bonds are at nearly 90 ^o angle to equitorial lone pairs so faces maximum repulsion.To minimize repulsion there is  lenthening of the axial bonds .
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Hello,
  In AsF₃,AsF₄^-, AsF₄⁺,AsF₆^-, what does A imply? Is it another element?

 Hello,

This  question is about the bond lengths of Arsenic trifluoride, Arsenic tetrafluoride cation and anion, hexafluoroarsinate ion(anion).

Quote from: Dhamnekar Winod on October 05, 2020, 11:31:10 AM
Hello,

This  question is about the bond lengths of Arsenic trifluoride, Arsenic tetrafluoride cation and anion, hexafluoroarsinate ion(anion).

As is Arsenic element

Quote from: uma on October 07, 2020, 07:44:55 PM
As is Arsenic element

Bond length order-
AsF₄⁺  < AsF₃   <AsF₆^-

In AsF3 (sp3) and AsF4+ (sp3)bond lengths are comparable as orbitals involved are same. However lone pairs on As in ASF₃ will make them slightly longer than AsF₄⁺.
In AsF6- however sp3d2 orbitals are involved which are bigger than sp3 orbitals so bond lengh in AsF₆^{- i}s more than AsF₃ and AsF₄⁺


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