Question

Which of the following have undistorted octahedral structures?
1. $S{F}_6$
2. $P{F}_6^{-}$
3. $Si{F}_6^{2-}$
4. $Xe{F}_6$
Select the correct answer using the codes given below:

• A. 2, 3 and 4
• B. 1, 3 and 4
• C. 1, 2 and 3
• D. 1, 2 and 4

Answer 1

The Correct Option is C

The structures of these species can be found out by knowing the hybridisation.The atomic number of $S=16$Electronic configuration of $\mathrm{P}=1{\mathrm{s}}^{2 }2{\mathrm{s}}^{2 }2{\mathrm{p}}^6 3{\mathrm{s}}^2 3{\mathrm{p}}^3$.Since, SF is spd hybridised having 6 bond pairs, the geometry is regular octahedral.2. $P{F}_6^{-}$Atomic number of $P= 15$Electronic configuration of $\mathrm{P}=1{\mathrm{s}}^{2 }2{\mathrm{s}}^{2 }2{\mathrm{p}}^6 3{\mathrm{s}}^2 3{\mathrm{p}}^3$Hybridisation is given as:$H=S.A+\frac{1}{2}(V-nE\pm C)$.......(i)where, S.A = No. of surrounding atomsV = Number of valence electrons on the central atomn = Number of anionE = Charge on the anionC = Total charge on the species.Thus, for $P{F}_6^{-}$S.A = 6V = 5n = 6E = 1C = -1Substituting the values in equation (i), we get$H=6+\frac{1}{2}(5-6+1)$= 6 Thus, the hybridisation is sp³d² having 6 bond pairs.  Therefore, the geometry is regular octahedral.3. $Si{F}_6^{2-}$Atomic no. of Si = 14Electronic configuration of $\mathrm{Si}=1 {\mathrm{s}}^{2}2 {\mathrm{s}}^{2}2{\mathrm{p}}^{6}3 {\mathrm{s}}^{2}3{\mathrm{p}}^2$S.A = 6V = 4n = 6E = 1C = -2Substituting values in equation (i), we get$H=6+\frac{1}{2}(4-6+1)$= 6Thus, the hybridisation is sp³d² having 6 bond pairs. Therefore, the geometry is regular octahedral.4. XeF6Atomic no. of Xe = 54Electronic configuration of $\mathrm{Xe}=\left[\mathrm{Kr}\right]4 {\mathrm{d}}^{10}5 {\mathrm{s}}^{2}5{\mathrm{p}}^6$S.A = 6V = 8n = 6E = 1C = 0Substituting values in equation (i), we get$H=6+\frac{1}{2}(8-6)$$=6+1$$=7$Thus, hybridisation is sp³³ and geometry should be pentagonal bipyramidal .But there are 6 bond pairs and one lone pair due to which XeF acquires a distorted octahedral geometry.

Hence, the correct option is (C): 1, 2 and 3