Understanding Bond Angles in Hydrides
The bond angles in various hydrides of Group 15 elements (NH3, PH3, AsH3, SbH3, BiH3) differ due to variations in their molecular geometries and the influence of lone pairs on the central atom.
Factors Influencing Bond Angles
- Hybridization: NH3 has sp3 hybridization, leading to a bond angle of approximately 107 degrees due to lone pair-bond pair repulsion.
- Lone Pairs: NH3 has one lone pair which distorts the bond angle. In contrast, PH3, AsH3, SbH3, and BiH3 have less effective lone pair repulsion due to their larger atomic sizes and increased bond length.
Order of Bond Angles
- NH3: 107 degrees (due to strong lone pair repulsion)
- PH3: 93.5 degrees (larger atomic size leads to lower bond angle)
- AsH3: ~92 degrees (further increase in size leads to weaker repulsion)
- SbH3: ~91 degrees (even less repulsion)
- BiH3: ~90 degrees (largest atom, minimal repulsion)
Final Order of Bond Angles
- The correct order of bond angles from largest to smallest is:
- NH3 > PH3 > AsH3 > SbH3 > BiH3
Conclusion
The trend in bond angles reflects the increasing size and decreasing electronegativity of the central atom, which results in weaker lone pair-bond pair interactions. Understanding this trend is crucial for predicting molecular behavior in various chemical contexts, particularly in JEE.