Ch.9 - Molecular Geometry and Bonding Theories

Brown - Chemistry: The Central Science 14th Edition

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Brown 14th Edition

Ch.9 - Molecular Geometry and Bonding Theories

Problem 86a

Chapter 9, Problem 86a

An AB2 molecule is described as having a tetrahedral geometry. (a) How many nonbonding domains are on atom A?

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Identify the central atom in the molecule AB2, which is atom A.

Understand that a tetrahedral geometry implies that there are four electron domains around the central atom. These domains can be either bonding pairs of electrons or lone pairs (nonbonding pairs).

Recognize that in the molecule AB2, there are two bonds between atom A and two B atoms. These two bonds account for two of the electron domains.

Since the geometry is tetrahedral with four electron domains and only two are used for bonding, the remaining two domains must be nonbonding.

Conclude that there are two nonbonding domains (lone pairs) on atom A in the AB2 molecule with tetrahedral geometry.

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Key Concepts

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

Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. In the case of an AB2 molecule with tetrahedral geometry, the central atom A is surrounded by two B atoms and the spatial arrangement is determined by the repulsion between electron pairs, including both bonding and nonbonding pairs.

VSEPR Theory

Valence Shell Electron Pair Repulsion (VSEPR) theory is a model used to predict the geometry of individual molecules based on the repulsion between electron pairs in the valence shell of the central atom. According to VSEPR, the shape of the molecule is determined by minimizing the repulsion between these electron pairs, which can include bonding pairs and lone pairs.

Nonbonding Domains

Nonbonding domains refer to regions in a molecule where electron pairs are present but are not involved in bonding with other atoms. In a tetrahedral AB2 molecule, the presence of nonbonding domains on atom A affects the overall geometry and can influence the angles between the bonded atoms, which is crucial for understanding the molecular shape.

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Consider the following XF₄ ions: PF₄^-, BrF₄^-, ClF₄⁺, and AlF₄^-. (a) Which of the ions have more than an octet of electrons around the central atom?

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Consider the following XF4 ions: PF4-, BrF4-, ClF4+, and AlF4-. (c) Which of the ions will have an octahedral electron-domain geometry?

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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?

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Textbook Question

Consider the molecular orbitals of the P2 molecule. Assume that the MOs of diatomics from the third row of the periodic table are analogous to those from the second row. (c) For the P2 molecule, how many electrons occupy the MO in the figure?

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Textbook Question

An AB2 molecule is described as having a tetrahedral geometry. (b) Based on the information given, which of the following is the molecular geometry of the molecule: (i) linear, (ii) bent, (iii) trigonal planar, or (iv) tetrahedral?

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