Textbook Question
(a) Explain why BrF4- is square planar, whereas BF4- is tetrahedral.
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Ch.9 - Molecular Geometry and Bonding Theories
Chapter 9, Problem 34
Name the proper three-dimensional molecular shapes for each of the following molecules or ions, showing lone pairs as needed: (a) ClO2- (b) SO4 2- (c) NF3 (d) CCl2Br2 (e) SF4 2+
Verified step by step guidance1
Step 1: Determine the total number of valence electrons for each molecule or ion. For example, for ClO2-, count the valence electrons from Cl and O, and add one more for the negative charge.
Step 2: Draw the Lewis structure for each molecule or ion. Arrange the atoms to satisfy the octet rule, and place any extra electrons as lone pairs on the central atom.
Step 3: Use the VSEPR (Valence Shell Electron Pair Repulsion) theory to determine the electron pair geometry around the central atom. Consider both bonding pairs and lone pairs of electrons.
Step 4: Identify the molecular geometry by considering only the positions of the atoms (ignoring lone pairs). For example, if there are four electron pairs and one is a lone pair, the molecular shape is trigonal pyramidal.
Step 5: Name the molecular shape for each molecule or ion based on the arrangement of atoms. For example, a molecule with four bonding pairs and no lone pairs is tetrahedral.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
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, electron pairs, including lone pairs, will arrange themselves to minimize repulsion, leading to specific molecular shapes such as linear, trigonal planar, tetrahedral, and octahedral.
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Lone Pairs and Bonding Pairs
In molecular geometry, lone pairs are pairs of valence electrons that are not involved in bonding, while bonding pairs are shared between atoms. Lone pairs occupy more space than bonding pairs, affecting the overall shape of the molecule. Understanding the distinction between these pairs is crucial for accurately predicting molecular geometry using VSEPR Theory.
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Hybridization
Hybridization is the concept of mixing atomic orbitals to form new hybrid orbitals that can accommodate the bonding and lone pairs in a molecule. This process helps explain the geometry of molecules by determining the types of bonds formed and the angles between them. For example, sp3 hybridization leads to tetrahedral shapes, while sp2 results in trigonal planar arrangements.
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Related Practice
Textbook Question
(b) How would you expect the H¬X¬H bond angle to vary in the series H2O, H2S, H2Se? Explain. (Hint: The size of an electron pair domain depends in part on the electronegativity of the central atom.)
Textbook Question
(a) Does CS2 have a dipole moment? If so, in which direction does the net dipole point? (b) Does SO2 have a dipole moment? If so, in which direction does the net dipole point?
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