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Ch.9 - Molecular Geometry and Bonding Theories
All textbooksBrown 14th EditionCh.9 - Molecular Geometry and Bonding TheoriesProblem 25b,c,d,e,f
Chapter 9, Problem 25b,c,d,e,f

Give the electron-domain and molecular geometries for the following molecules and ions: (b) AsCl5 (c) NO2- (d) CS2 (e) SF4 (f) BrF5

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Step 1: Draw the Lewis structure for the molecule or ion. For NO2-, the Lewis structure would have Nitrogen in the center, bonded to two Oxygen atoms. There is also an extra electron due to the negative charge, which is placed on the Nitrogen atom as a lone pair.
Step 2: Determine the electron-domain geometry. This is based on the number of electron domains - regions where electrons are most likely to be found. These include bonding pairs and lone pairs of electrons. For NO2-, there are three electron domains (two bonding and one lone pair), so the electron-domain geometry is trigonal planar.
Step 3: Determine the molecular geometry. This is based on the positions of the atoms, not the electron domains. For NO2-, the molecular geometry is bent or V-shaped, because the lone pair of electrons on the Nitrogen atom pushes the Oxygen atoms down, creating a bent shape.
Step 4: Remember that the presence of lone pairs can distort the shape of the molecule from the basic shape predicted by the number of bonding pairs alone. In this case, the lone pair on Nitrogen distorts the shape from a perfect trigonal planar to a bent shape.
Step 5: Finally, it's important to note that the actual bond angles in the molecule can be slightly less than the ideal angles predicted by the electron-domain geometry, due to the greater repulsion of lone pairs compared to bonding pairs.

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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 a molecule. It is determined by the number of electron domains, which can include single bonds, double bonds, triple bonds, and lone pairs. For example, a molecule with four electron domains adopts a tetrahedral geometry.
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Molecular Geometry

Molecular geometry describes the three-dimensional arrangement of the atoms in a molecule, considering only the positions of the nuclei and not the lone pairs. It is influenced by the electron-domain geometry but differs when lone pairs are present, as they occupy space and can alter bond angles. For instance, in a molecule with a tetrahedral electron-domain geometry and one lone pair, the molecular geometry would be trigonal pyramidal.
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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 around a central atom. According to VSEPR, electron pairs will arrange themselves to minimize repulsion, leading to specific molecular shapes. This theory helps in determining both electron-domain and molecular geometries by considering the number and type of electron domains.
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Related Practice
Textbook Question

Give the electron-domain and molecular geometries for the following molecules and ions: (a) BeF2

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Textbook Question

Draw the Lewis structure for each of the following molecules or ions, and predict their electron-domain and molecular geometries: (a) AsF3 (b) CH3+ (c) BrF3 (d) ClO3- (e) XeF2 (f) BrO2-

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Textbook Question

The figure that follows contains ball-and-stick drawings of three possible shapes of an AF4 molecule. (a) For each shape, give the electron-domain geometry on which the molecular geometry is based. i.

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Textbook Question

The figure that follows contains ball-and-stick drawings of three possible shapes of an AF4 molecule. (a) For each shape, give the electron-domain geometry on which the molecular geometry is based. iii.

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