Multiple Choice
Which of the following best describes the molecular geometry and polarity of carbon tetrabromide (CBr_4)?
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12. Molecular Shapes & Valence Bond Theory
Molecular Geometry
Multiple Choice
The molecular geometry of the PF3 molecule is ________, and this molecule is ________.
A
linear; nonpolar
B
tetrahedral; polar
C
trigonal planar; nonpolar
D
trigonal pyramidal; polar
Verified step by step guidance1
Step 1: Determine the Lewis structure of PF3. Phosphorus (P) is the central atom bonded to three fluorine (F) atoms. Phosphorus has 5 valence electrons, and each fluorine has 7 valence electrons.
Step 2: Count the total valence electrons: 5 (from P) + 3 × 7 (from F) = 26 valence electrons. Use these electrons to form three P-F single bonds and place lone pairs to satisfy the octet rule.
Step 3: Identify the number of bonding pairs and lone pairs around the central phosphorus atom. There are three bonding pairs (from the three P-F bonds) and one lone pair on phosphorus.
Step 4: Use VSEPR theory to predict the molecular geometry. With three bonding pairs and one lone pair, the electron pair geometry is tetrahedral, but the molecular shape (geometry) is trigonal pyramidal because the lone pair affects the shape.
Step 5: Determine polarity. Since fluorine is more electronegative than phosphorus and the molecule is asymmetrical due to the lone pair, the dipoles do not cancel out, making PF3 a polar molecule.
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