QQuestionChemistry
QuestionChemistry
Explain why BH^3 is trigonal planar and NH^3 is trigonal pyramidal.
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Answer
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Step 1:I'll solve this molecular geometry problem step by step:
Step 2:: Understand Electron Geometry Basics
The molecular geometry of a molecule depends on: - Number of central atom's valence electrons - Number of bonding and non-bonding electron pairs - Electron pair arrangement (electron geometry)
Step 3:: Analyze BH^3 Electron Configuration
- Total electron configuration: $$3 + (3 \times 1) = 6$$ electrons
- Boron (B) has 3 valence electrons - Each hydrogen (H) contributes 1 electron - These form 3 single bonds - No lone pairs on central boron atom
Step 4:: BH^3 Molecular Geometry
- Bond angles: $$120^{\circ}
- 3 bonding electron pairs - 0 lone pairs - Electron geometry: Trigonal planar - Symmetric electron distribution around central boron
Step 5:: Analyze NH^3 Electron Configuration
- Total electron configuration: $$5 + (3 \times 1) = 8$$ electrons
- Nitrogen (N) has 5 valence electrons - Each hydrogen (H) contributes 1 electron - 3 single bonds - 1 lone pair on central nitrogen
Step 6:: NH^3 Molecular Geometry
- Bond angles slightly less than $$109.5^{\circ}$$ due to lone pair repulsion
- 3 bonding electron pairs - 1 lone pair - Electron geometry: Tetrahedral - Molecular geometry: Trigonal pyramidal
Final Answer
- BH^3 is trigonal planar due to symmetric electron distribution with no lone pairs - NH^3 is trigonal pyramidal due to the presence of a lone pair on the central nitrogen atom, causing slight distortion from tetrahedral geometry
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