Multiple Choice
What is the molecular geometry of CHClO (formaldehyde)?
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12. Molecular Shapes & Valence Bond Theory
Molecular Geometry
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What is the molecular geometry of PF_3?
A
Trigonal planar
B
Tetrahedral
C
Trigonal pyramidal
D
Bent
Verified step by step guidance1
Determine the Lewis structure of PF_3 by counting the total valence electrons: Phosphorus (P) has 5 valence electrons, and each Fluorine (F) has 7 valence electrons. Since there are 3 fluorines, total valence electrons = 5 + (3 × 7) = 26 electrons.
Draw the skeletal structure with phosphorus as the central atom bonded to three fluorine atoms. Distribute the remaining electrons to satisfy the octet rule for each atom, placing lone pairs where necessary.
Count the number of bonding pairs and lone pairs around the central phosphorus atom. In PF_3, there are three bonding pairs (one for each P-F bond) and one lone pair on phosphorus.
Use the VSEPR (Valence Shell Electron Pair Repulsion) theory to predict the molecular geometry. Four regions of electron density (3 bonding pairs + 1 lone pair) around phosphorus correspond to a tetrahedral electron geometry.
Since one of the four regions is a lone pair, the molecular geometry (shape) is trigonal pyramidal, not tetrahedral or trigonal planar.
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