Chemistry - A Molecular Science

5.0 Introduction

5.6 Determining Lewis Structures

5.1 The Covalent Bond

5.7 Resonance

5.2 Bond Polarity

5.8 Formal Charge and Oxidation State

5.3 Naming Binary Covalent Compound

s

5.9 Practice with Lewis Structures

5.4 Lewis Symbols of the Elements

5.10 Chapter Summary and Objectives

5.5

Lewis Structures o

f Diatomic Molecules

5.11

Exercises

Chapter 5 The Covalent Bond

5.0

INTRODUCTION

We concluded Chapter 4 with the observation that

ionic substances

are extended networks

of large numbers of ions and not individual molecules. For example, in a crystal of NaCl, six chloride ions are bound to each sodium i

on, but no one chloride ion can be clearly

identified with any one sodium ion. This is

because the charge on the ions is spherical,

which makes the ionic bond non-directional. However, in compounds that are composed only of nonmetals, the bond between the atoms is

directional. For example, in ICl, each

iodine atom is bound to a clearly identifiable c

horine atom, so there are distinct molecules

of ICl, and ICl is said to be a

molecular substance

. Bonds that are directional are called

covalent bonds

. Whereas ionic bonds usually form

between metals and nonmetals,

covalent bonds are formed between nonmetals.

We discuss the nature of the covalent bond

in this chapter, and then, in Chapter 6, we look at the impact that directional bonds have on the structures of molecules and consider two theories for the covalent bond. THE OBJECTIVES OF CHAPTER 5 ARE TO: •

discuss the theory of the covalent bond; distinguish between the ionic bond and the covalent bond; • describe how covalent compounds are named; • define Lewis structures and •

show how to generate them;

define bond polarity; • describe resonance and its effects; • define formal charge and explain how to determine it; and • distinguish between formal charge and oxidation state. •

Chapter 5 The Covalent Bond

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