Multiple Choice
What is the molecular geometry of ammonia (NH_3)?
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12. Molecular Shapes & Valence Bond Theory
Molecular Geometry
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What is the molecular geometry around the nitrogen atom in CH3NH2?
A
Trigonal pyramidal
B
Trigonal planar
C
Bent
D
Tetrahedral
Verified step by step guidance1
Identify the central atom for which you want to determine the molecular geometry. In CH3NH2, focus on the nitrogen atom in the NH2 group.
Determine the number of regions of electron density (bonding and lone pairs) around the nitrogen atom. Nitrogen in NH2 is bonded to two hydrogen atoms and one carbon atom, and it also has one lone pair of electrons.
Count the total number of electron groups around nitrogen: 3 bonding pairs (2 H + 1 C) and 1 lone pair, making 4 regions of electron density.
Use the VSEPR (Valence Shell Electron Pair Repulsion) theory to predict the shape. Four regions of electron density correspond to a tetrahedral electron geometry, but the presence of one lone pair changes the molecular shape.
Recognize that with one lone pair and three bonded atoms, the molecular geometry is trigonal pyramidal around the nitrogen atom.
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