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Ch.9 - Molecular Geometry and Bonding Theories
All textbooksBrown 15th EditionCh.9 - Molecular Geometry and Bonding TheoriesProblem 86b
Chapter 9, Problem 86b

An AB3 molecule is described as having a trigonal-bipyramidal electron-domain geometry b. Based on the information given, which of the following is the molecular geometry of the molecule:
i. trigonal planar
ii. trigonal pyramidal
iii. T-shaped or
iv. tetrahedral?

Verified step by step guidance
1
Identify the electron-domain geometry of the molecule. The problem states that the AB3 molecule has a trigonal-bipyramidal electron-domain geometry.
Understand the electron-domain geometry: A trigonal-bipyramidal geometry typically involves five electron domains around the central atom.
Determine the number of lone pairs: Since the molecule is AB3, it has three bonded atoms and two lone pairs on the central atom.
Analyze the effect of lone pairs: In a trigonal-bipyramidal geometry, lone pairs prefer equatorial positions to minimize repulsion. With two lone pairs, the molecular geometry becomes T-shaped.
Conclude the molecular geometry: Based on the analysis, the molecular geometry of the AB3 molecule with two lone pairs in a trigonal-bipyramidal electron-domain geometry is T-shaped.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Electron-Domain Geometry

Electron-domain geometry refers to the spatial arrangement of all electron domains (bonding and lone pairs) around a central atom. In the case of an AB3 molecule with trigonal-bipyramidal electron-domain geometry, there are five electron domains, which can include bonding pairs and lone pairs. This geometry helps predict the overall shape of the molecule based on the repulsion between these electron domains.
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Molecular Geometry

Molecular geometry describes the three-dimensional arrangement of atoms in a molecule, considering only the positions of the nuclei of the atoms. It is influenced by the electron-domain geometry but differs when lone pairs are present. For an AB3 molecule with trigonal-bipyramidal electron-domain geometry, the molecular geometry can vary depending on the presence of lone pairs, leading to shapes such as trigonal planar or T-shaped.
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VSEPR Theory

Valence Shell Electron Pair Repulsion (VSEPR) theory is a model used to predict the geometry of molecules based on the repulsion between electron pairs. According to VSEPR, electron pairs will arrange themselves to minimize repulsion, leading to specific molecular shapes. This theory is essential for determining the molecular geometry of an AB3 molecule with trigonal-bipyramidal electron-domain geometry, as it helps identify the resulting shape based on the arrangement of bonding and lone pairs.
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Related Practice
Textbook Question

The iodine bromide molecule, IBr, is an interhalogen compound. Assume that the molecular orbitals of IBr are analogous to the homonuclear diatomic molecule F2. (a) Which valence atomic orbitals of I and of Br are used to construct the MOs of IBr?

Textbook Question

The iodine bromide molecule, IBr, is an interhalogen compound. Assume that the molecular orbitals of IBr are analogous to the homonuclear diatomic molecule F2. (c) One of the valence MOs of IBr is sketched here. Determine whether each of the following statements about this orbital is true: i. This is an antibonding orbital. ii. The larger contribution is from the I atom. iii. The energy of the molecular orbital is closer in energy to the valence atomic orbitals of Br than to those of I.

Textbook Question

An AB3 molecule is described as having a trigonal-bipyramidal electron-domain geometry. a. How many nonbonding domains are on atom A?

Textbook Question

Fill in the blank spaces in the following chart. If the molecule column is blank, find an example that fulfills the conditions of the rest of the row. Molecule Electron-Domain Hybridization Dipole Geometry of Central Atom Moment? Yes or No CO2 sp3 Yes sp3 No Trigonal planar No SF4 Octahedral No sp2 Yes Trigonal bipyramidal No XeF2

Textbook Question

The lactic acid molecule, CH3CH(OH)COOH, gives sour milk its unpleasant, sour taste. e. What are the approximate bond angles around each carbon atom in the molecule?