Ch.9 - Molecular Geometry and Bonding Theories

Problem 28a3

Chapter 9, Problem 28a3

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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Identify the central atom (A) and the surrounding atoms (F) in the AF4 molecule.

Determine the number of electron domains around the central atom. In this case, there are 5 electron domains (4 bonding pairs and 1 lone pair).

Recognize that the electron-domain geometry for 5 electron domains is trigonal bipyramidal.

Understand that the molecular geometry is derived from the electron-domain geometry by considering only the positions of the atoms. With one lone pair, the molecular geometry is seesaw.

Conclude that the electron-domain geometry for the given AF4 molecule shape is trigonal bipyramidal, and the molecular geometry is seesaw.

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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 helps predict the overall shape of the molecule based on the number of electron domains. For example, a central atom with four electron domains will have a tetrahedral electron-domain geometry.

Molecular Geometry

Molecular geometry describes the three-dimensional arrangement of the atoms in a molecule, which is influenced by the electron-domain geometry. While electron domains include lone pairs, molecular geometry focuses solely on the positions of the atoms. For instance, a tetrahedral electron-domain geometry can lead to different molecular geometries, such as tetrahedral or trigonal pyramidal, depending on the presence of lone pairs.

VSEPR Theory

Valence Shell Electron Pair Repulsion (VSEPR) theory is a model used to predict the shape 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 geometries. This theory is essential for understanding how the shapes of molecules, like AF4, are determined by their electron-domain arrangements.

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Related Practice

Textbook Question

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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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.

The figure that follows contains ball-and-stick drawings of three possible shapes of an AF4 molecule. (c) Which of the following elements will lead to an AF4 molecule with the shape in (iii): Be, C, S, Se, Si, Xe? i.

ii.

iii.

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Textbook Question

Give the approximate values for the indicated bond angles in the following molecules: (a)