Question

Which one of the following pairs is isostructural (i.e., having the same shape and hybridization)?

• A. $[ BCl_3 $ and $ BrCl_3^- ]$
• B. $[ NH_3 $ and $ NO_3^- ]$
• C. $NF_3 $ and $ BF_3$
• D. $[BF^{-}_{4} $ and $ NH^{+}_4]$

Answer 1

The Correct Option is D

$BF _{4}^{-}$hybridisation $s p^{3}$, tetrahedral structure.
$NH _{4}^{+}$hybridisation $s p^{3}$, tetrahedral structure.

Answer 2

To determine which pair is isostructural, we need to analyze the shape and hybridization of each molecule/ion in the pairs.

 1. [BCl3 and BrCl3−]

- BCl3: 
 - Boron trichloride has the central boron atom with three chlorine atoms.
 - Boron has 3 valence electrons, and each chlorine contributes 1 electron.
 - Total valence electrons: \(3 + 3 \times 7 = 24\) electrons.
 - The structure is trigonal planar with an sp^2 hybridization.

- BrCl3−:
 - Bromine trichloride anion has the central bromine atom with three chlorine atoms and one extra electron (negative charge).
 - Bromine has 7 valence electrons, each chlorine has 7, and there is 1 extra electron due to the negative charge.
 - Total valence electrons: \(7 + 3 \times 7 + 1 = 29\) electrons.
 - The structure is T-shaped with an sp^3d hybridization.

Since BCl3 is trigonal planar (sp^2) and BrCl3− is T-shaped (sp^3d), this pair is not isostructural.

2. [NH3 and NO3−]

- NH3:
 - Ammonia has the central nitrogen atom with three hydrogen atoms and one lone pair.
 - Nitrogen has 5 valence electrons, and each hydrogen contributes 1 electron.
 - Total valence electrons: \(5 + 3 \times 1 = 8\) electrons.
 - The structure is trigonal pyramidal with an sp^3 hybridization.

- NO3−:
 - Nitrate anion has the central nitrogen atom with three oxygen atoms and one extra electron (negative charge).
 - Nitrogen has 5 valence electrons, each oxygen has 6, and there is 1 extra electron due to the negative charge.
 - Total valence electrons: \(5 + 3 \times 6 + 1 = 24\) electrons.
 - The structure is trigonal planar with an sp^2 hybridization.

Since NH3 is trigonal pyramidal (sp^3) and NO3− is trigonal planar (sp^2), this pair is not isostructural.

3. [NF3 and BF3]

- NF3:
 - Nitrogen trifluoride has the central nitrogen atom with three fluorine atoms and one lone pair.
 - Nitrogen has 5 valence electrons, and each fluorine contributes 7 electrons.
 - Total valence electrons: \(5 + 3 \times 7 = 26\) electrons.
 - The structure is trigonal pyramidal with an sp^3 hybridization.

- BF3:
 - Boron trifluoride has the central boron atom with three fluorine atoms.
 - Boron has 3 valence electrons, and each fluorine contributes 7 electrons.
 - Total valence electrons: \(3 + 3 \times 7 = 24\) electrons.
 - The structure is trigonal planar with an sp^2 hybridization.

Since NF3 is trigonal pyramidal (sp^3) and BF3 is trigonal planar (sp^2), this pair is not isostructural.

 4. [BF4− and NH4+]

- BF4−:
 - Tetrafluoroborate anion has the central boron atom with four fluorine atoms.
 - Boron has 3 valence electrons, each fluorine has 7, and there is 1 extra electron due to the negative charge.
 - Total valence electrons: \(3 + 4 \times 7 + 1 = 32\) electrons.
 - The structure is tetrahedral with an sp^3 hybridization.

- NH4+:
 - Ammonium cation has the central nitrogen atom with four hydrogen atoms.
 - Nitrogen has 5 valence electrons, each hydrogen has 1, and there is 1 fewer electron due to the positive charge.
 - Total valence electrons: \(5 + 4 \times 1 - 1 = 8\) electrons.
 - The structure is tetrahedral with an sp^3 hybridization.

Since both BF4− and NH4+ are tetrahedral (sp^3), this pair is isostructural.

 Conclusion

The correct isostructural pair is Option 4:

\[\text{[BF4− and NH4+]}\]