Chemistry - A Molecular Science

(Nora) #1
Chapter 4 The Ionic Bond

4.0 Introduction

4.5 Polyatomic Ions

4.1 Ionic Bonding

4.6 Naming Ionic Compounds

4.2 Naming and Predicting Ions

4.7 Structure of Ionic Compounds

4.3 Relative Sizes of Ions

4.8 Chapter Summary and Objectives

4.0


INTRODUCTION


The valence electrons in metals are at relativ


ely high potential energies, so metals have


low ionization energies, while the unfilled valen


ce orbitals in nonmetals are at relatively


low potential energies, so nonmetals have high


electronegativities. Electrons seek to lower


their potential energy whenever possible, so


when metal atoms combine with nonmetal


atoms, the high-energy valence electrons of the metal are


transferred


to the low-energy


orbitals of the nonmetal. The result is that


the metal becomes a cation and the nonmetal


becomes an anion. The oppositely charged ions are held together by an electrostatic force called an


ionic bond


, and the compounds between me


tals and nonmetals are called


ionic


compounds


. Ionic compounds are not molecular becau


se each cation in an ionic solid is


surrounded by a number of anions, none of whic


h is uniquely associated with the cation.


The situation is quite different in the


bonds between two nonmetals because the energy


difference between the valence orbitals of tw


o nonmetals is relatively small. Thus, when


nonmetals bond to one another, the valence electrons are


shared


rather than transferred.


The resulting bond is known as a


covalent bond


, and compounds composed only of


nonmetals are called


covalent



  • or


molecular


, as individual molecules are readily


identified. The properties of ionic and molecular substances are quite different. In this chapter, we discuss the ionic bond and ionic compounds. The covalent bond and molecular compounds will be discussed in Chapters 5 and 6.


4.4 Oxidation States

4.9 Exercises
* Although covalent compounds are not

discussed until the next chapter,

we define them here so that we c

an compare ionic compounds to them

in this chapter.

THE OBJECTIVES OF CHAPTER 4 ARE TO: •

discuss the properties of ions;

(^) •
define oxidation states and show how they are determined in ions and molecules;
(^) •
demonstrate how to name ionic compounds;
(^) •
explain how to predict the formulas of binary ionic compounds; and
(^) •
explain why ionic compounds are not molecular.
Chapter 4 The Ionic Bond
© by
North
Carolina
State
University

Free download pdf