Question

In the below reaction, geometry of BCl3, X respectively are \(\text{BC}_{3} + \text{NH}_{3} \rightarrow X\)

• A. Pyramidal, tetrahedral
• B. Pyramidal, octahedral
• C. Trigonal planar, tetrahedral
• D. Trigonal planar, octahedral

Hint:

When forming adducts, the geometry of the resulting compound often changes from the initial geometry of the individual components.

Answer 1

The Correct Option is C

To determine the molecular geometry of BCl₃ and the product X in the provided reaction, we need to consider the VSEPR (Valence Shell Electron Pair Repulsion) theory. This theory helps predict the geometry of molecules based on minimizing the repulsion between electron pairs around a central atom.

Step 1: Determine the geometry of BCl₃. Boron is the central atom in BCl₃ and has three valence electrons. Chlorine has seven valence electrons and forms a single bond with boron, using one of boron's valence electrons. Since BCl₃ has three bond pairs and no lone electron pairs on the boron atom, it adopts a trigonal planar geometry to minimize electron pair repulsion.

Step 2: Predict the geometry of the species X. In the reaction BCl₃ + NH₃, NH₃ donates its lone pair to form a coordinate bond with BCl₃. Through this process, a tetrahedral geometry is formed around the boron atom in the adduct, as there are now four regions of electron density (three from B-Cl bonds and one from N-B coordinate bond).

Therefore, the geometry of BCl₃ is trigonal planar, and the geometry of the compound X (formed after the reaction with NH₃) is tetrahedral.

Correct Answer: Trigonal planar, tetrahedral