In the molecule N ( SiH 3 ) 3 , the N − Si bond is shorter than expected from the sum of covalent radii. This is attributed to p π − d π interactions. If we replace Si with Ge, and then Sn, how do

Question

In the molecule N ( SiH 3 ​ ) 3 ​ , the N − Si bond is shorter than expected from the sum of covalent radii. This is attributed to p π − d π interactions. If we replace Si with Ge, and then Sn, how does the π -bond strength Δ E π ​ scale, and what is the primary reason?

TestHub · Accepted Answer

Question Explanation: Explains how energy mismatch and size affect back-bonding strength.

Concept: $p π - d π$ Back-bonding and Orbital Size

Solution: -

1. Back-bonding requires both good spatial overlap and similar energy levels.

2. As we go Si → Ge → Sn, the d-orbitals become more diffused and higher in energy relative to the 2p orbital of Nitrogen.

3. The overlap integral S decreases due to size mismatch (2p − 3d > 2p − 4d > 2p − 5d).

4. From perturbation theory, the stabilization energy

$Δ E \approx \frac{H _{ab}^{2}}{E _{a} - E _{b}} A s E_{a} - E_{b}$

increases and H_ab

(overlap term) decreases, the bond strength drops sharply.

Final Answer: ΔE_π increases because d-orbitals become more available.

Chemistry - CHEMICAL BONDING Question with Solution | TestHub

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