Chemistry - A Molecular Science

6.0 Introduction

6.4 Valence Bond Theory and Hybridization

6.1 Molecular Shapes

6.5 Molecular Orbital Theor

y and Delocalized Bon

ds

6.2 Central Atoms with Expanded Valence

Shells

6.6 Chapter Summary and Objectives

6.3 Larger Molecules

6.7 Exercises

Chapter 6 Molecular Structure & Bonding

6.0

INTRODUCTION

A molecule is characterized by its three-dime

nsional structure, which is the arrangement

of its nuclei. The positions of the nuclei

are determined by the lengths of the bonds

between them and the angles at which those bon

ds intersect. A molecular structure plays a

key role in determining both the physical a

nd chemical properties of the molecule. The

positions, strengths, and polarities of the bonds

influence a molecule's reactivity. Size and

shape are primary factors in governing the ce

llular processes in which biomolecules, like

proteins and DNA, participate. The structure of

a molecule dictates whether it is a solid,

liquid, or gas at a given set of conditions.

In this chapter, we apply increasingly sophisticated models to the study of structure

and bonding. We first use the valence-shell

electron-pair repulsion model (electrostatic

arguments) to describe the arrangements of

electron groups around an atom. Then we

explain how and why bonds are formed w

ith valence bond theory. We conclude the

chapter with a brief introduction into molecular orbital theory to explain shortcomings in the valence bond theory and to introduce

the electronic structure of molecules.

THE OBJECTIVES OF CHAPTER 6 ARE TO: •

explain the VSEPR (

valence-

shell

electron-

pair r

epulsion) model and demonstrate how to use

it to predict the geometry of the electron regions around a central atom;

(^) •
show how to extend the VSEPR model to larger molecules;
(^) •
describe valence bond theory;
(^) •
distinguish between sigma and pi bonding;
(^) •
define hybridization and show how it is used;
(^) •
use molecular orbital theory to explain delocalized bonding; and
(^) •
infer the structure and bonding in a
molecule from its Lewis structure.
Chapter 6 Molecular Structure & Bonding
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