Multiple Choice
Which compound below is a polar molecule and has a linear molecular geometry?
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12. Molecular Shapes & Valence Bond Theory
Molecular Geometry
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Which of the following best describes the three-dimensional molecular geometry of NH_3?
A
Trigonal pyramidal
B
Trigonal planar
C
Bent
D
Tetrahedral
Verified step by step guidance1
Identify the central atom in the molecule NH_3, which is nitrogen (N).
Determine the number of valence electrons around the nitrogen atom. Nitrogen has 5 valence electrons, and each hydrogen contributes 1 electron, for a total of 8 electrons (or 4 electron pairs) around nitrogen.
Use the VSEPR (Valence Shell Electron Pair Repulsion) theory to predict the shape. The 4 electron pairs around nitrogen consist of 3 bonding pairs (with hydrogen atoms) and 1 lone pair.
According to VSEPR theory, the electron pairs arrange themselves to minimize repulsion, resulting in a tetrahedral electron pair geometry. However, the molecular geometry considers only the positions of atoms, not lone pairs.
Since there is one lone pair and three bonded atoms, the molecular geometry is 'trigonal pyramidal,' where the lone pair pushes the three hydrogen atoms downward, creating a pyramid shape.
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