Question

The reason(s) for the lower stability of $Si_2H_6$ compared to $C_2H_6$ is/are

• A. silicon is more electronegative than hydrogen
• B. Si-Si bond is weaker than C-C bond
• C. Si-H bond is weaker than C-H bond
• D. the presence of low-lying d-orbitals in silicon

Answer 1

The Correct Option is B, C, D

The stability of chemical compounds such as $Si_2H_6$ (disilane) and $C_2H_6$ (ethane) can be understood in terms of bond strengths and electronic configurations. Here, we explore three reasons for the lower stability of $Si_2H_6$ compared to $C_2H_6$:

1. Si-Si Bond Strength:
   The Si-Si bond in disilane is weaker than the C-C bond in ethane. This is primarily due to the larger size of the silicon atom compared to carbon. Larger atomic size of silicon leads to a longer bond length and weaker bond strength, as bond strength generally decreases with increasing bond length.
2. Si-H Bond Strength:
   The Si-H bond is also weaker than the C-H bond. This weaker bond is due to the difference in electronegativity between silicon and hydrogen compared to carbon and hydrogen. Since the electronegativity difference is less in Si-H, the bond is less polar and weaker, contributing to lower stability.
3. Low-lying d-Orbitals:
   The presence of low-lying d-orbitals in silicon can influence its bonding characteristics. These d-orbitals can participate in back bonding, but they also reduce the overlap efficiency of the bonds compared to the sp³ hybrid orbitals of carbon. This further weakens the Si-Si and Si-H bonds, reducing overall stability.

Other factors, such as silicon being more electronegative than hydrogen, do not directly impact the comparison between disilane and ethane in terms of stability. Thus, the correct reasons contributing to the lower stability of $Si_2H_6$ compared to $C_2H_6$ are:

• Si-Si bond is weaker than C-C bond
• Si-H bond is weaker than C-H bond
• The presence of low-lying d-orbitals in silicon