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Ch.9 - Molecular Geometry and Bonding Theories
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook
All textbooksBrown 14th EditionCh.9 - Molecular Geometry and Bonding TheoriesProblem 87a
Chapter 9, Problem 87a

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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Determine the number of valence electrons for each central atom: P, Br, Cl, and Al.
Add or subtract electrons based on the charge of the ion: add one electron for negative charges and subtract one for positive charges.
Calculate the total number of electrons around the central atom by adding the electrons from the fluorine atoms (each F contributes one electron to the central atom).
Check if the total number of electrons around the central atom exceeds 8, which would indicate more than an octet.
Identify which ions have central atoms with more than 8 electrons, indicating an expanded octet.

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Key Concepts

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

Octet Rule

The octet rule is a chemical principle that states atoms tend to bond in such a way that they have eight electrons in their valence shell, achieving a stable electron configuration similar to that of noble gases. This rule is particularly relevant for main group elements, which typically form bonds to fulfill this requirement. However, some elements, especially those in the third period and beyond, can expand their octet due to available d-orbitals.

Expanded Octet

An expanded octet occurs when an atom has more than eight electrons in its valence shell. This phenomenon is common in elements from the third period of the periodic table and beyond, such as phosphorus, sulfur, and chlorine, which can utilize their d-orbitals to accommodate additional electrons. Understanding which elements can expand their octet is crucial for predicting the bonding and structure of certain molecules and ions.
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Lewis Structures

Lewis structures are diagrams that represent the bonding between atoms in a molecule and the lone pairs of electrons that may exist. They are essential for visualizing the arrangement of electrons and determining whether an atom has achieved an octet or an expanded octet. By drawing Lewis structures for the given ions, one can easily identify the number of electrons surrounding the central atom and assess compliance with the octet rule.
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Related Practice
Textbook Question

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

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Textbook Question

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

Consider the molecule PF4Cl. (c) Predict the molecular geometry of PF4Cl. How did your answer for part (b) influence your answer here in part (c)?

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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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Textbook Question

Consider the molecule PF4Cl. (a) Draw a Lewis structure for the molecule, and predict its electron-domain geometry.

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