Multiple Choice
Which of the following molecules has a molecular structure that differs from its electron-pair geometry?
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12. Molecular Shapes & Valence Bond Theory
Molecular Geometry
Multiple Choice
What is the molecular geometry of NF_3?
A
Tetrahedral
B
Trigonal pyramidal
C
Bent
D
Trigonal planar
Verified step by step guidance1
Step 1: Determine the Lewis structure of NF_3 by counting the total valence electrons. Nitrogen has 5 valence electrons, and each fluorine has 7 valence electrons, so total valence electrons = 5 + 3 \(\times\) 7 = 26 electrons.
Step 2: Draw the nitrogen atom in the center bonded to three fluorine atoms with single bonds. Each bond accounts for 2 electrons, so 3 bonds use 6 electrons, leaving 20 electrons to be placed as lone pairs.
Step 3: Complete the octets of the fluorine atoms by placing 6 electrons (3 lone pairs) around each fluorine. This uses 18 electrons (3 fluorines \(\times\) 6 electrons each).
Step 4: Place the remaining 2 electrons as a lone pair on the nitrogen atom. Now nitrogen has 3 bonding pairs and 1 lone pair.
Step 5: Use VSEPR theory to determine the molecular geometry. With 3 bonding pairs and 1 lone pair, the electron geometry is tetrahedral, but the molecular shape (ignoring the lone pair) is trigonal pyramidal.
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