Multiple Choice
What is the molecular geometry of CO_2?
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12. Molecular Shapes & Valence Bond Theory
Molecular Geometry
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What is the molecular geometry of PH3?
A
Trigonal pyramidal
B
Trigonal planar
C
Bent
D
Tetrahedral
Verified step by step guidance1
Identify the central atom in PH3, which is phosphorus (P), and note that it is bonded to three hydrogen (H) atoms.
Determine the number of valence electrons on the central atom (phosphorus). Phosphorus has 5 valence electrons.
Count the total number of electron pairs around the phosphorus atom by adding the bonding pairs (3 P-H bonds) and lone pairs. Since phosphorus has 5 valence electrons and forms 3 bonds, it has 1 lone pair remaining.
Use the VSEPR (Valence Shell Electron Pair Repulsion) theory to predict the molecular geometry. With 3 bonding pairs and 1 lone pair, the electron pair geometry is tetrahedral, but the molecular shape is trigonal pyramidal because the lone pair affects the shape but is not seen in the molecular geometry.
Conclude that the molecular geometry of PH3 is trigonal pyramidal due to the presence of three bonded atoms and one lone pair on the central phosphorus atom.
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