Multiple Choice
Which of the following best describes the molecular geometry of an ammonia (NH_3) molecule?
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12. Molecular Shapes & Valence Bond Theory
Molecular Geometry
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Which of the following best describes the molecular geometry of the BF3 molecule?
A
Trigonal planar
B
Trigonal pyramidal
C
Tetrahedral
D
Bent
Verified step by step guidance1
Identify the central atom in the BF3 molecule, which is boron (B).
Determine the number of valence electrons around the central atom. Boron has 3 valence electrons, and each fluorine atom contributes 1 electron for bonding, making a total of 3 bonding pairs.
Use the VSEPR (Valence Shell Electron Pair Repulsion) theory to predict the molecular geometry. Since there are three bonding pairs and no lone pairs on the central atom, the electron pairs will arrange themselves to minimize repulsion.
According to VSEPR theory, three bonding pairs with no lone pairs on the central atom arrange themselves in a trigonal planar shape to be as far apart as possible (120° bond angles).
Conclude that the molecular geometry of BF3 is trigonal planar, not trigonal pyramidal, tetrahedral, or bent, because those geometries involve lone pairs or different numbers of bonding pairs.
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