Burdge/Overby, Chemistry: Atoms First, 2e FM | Page 14

PREFACE

xiv

C H aP te R 5

164

Ionic and Covalent Compounds

bch_lb
Thinking Outside the Box
Functional Groups
Many organic compounds are derivatives of alkanes in which one of the
H atoms has been replaced by a group of atoms known as a functional
group. The functional group determines many of the chemical properties of
a compound because it typically is where a chemical reaction occurs. Table
5.9 lists the names and provides ball-and-stick models of several important
functional groups.
Ethanol, for example, the alcohol in alcoholic beverages, is ethane
(C2H6) with one of the hydrogen atoms replaced by an alcohol (—OH) group.
Its name is derived from that of ethane, indicating that it contains two carbon
atoms.

ta B L e 5 .9

Ethanol
The molecular formula of ethanol can also be written C2H6O, but C2H5OH
conveys more information about the structure of the molecule. Organic
compounds and several functional groups are discussed in greater detail in
Chapter 24.

Organic Functional Groups
Name

Functional group

Alcohol

— OH

Aldehyde

— CHO

Carboxylic acid

— COOH

Amine

Molecular model

—NH2

Visualization. This text seeks to enhance student understanding through a variety of both unique
5.7 CovaLeNt BoNDINg IN text is SPeCIeS
and conventional visual techniques. A truly unique element in this IoNIC the inclusion of a distinctive feature entitled Visualizing compounds we have encountered have been either ionic, held together by ionicneeded to
Chemistry. These two-page spreads appear as bonding;
So far, the
or molecular, held together by covalent bonding; and the ions we have encountered have all been
REVISED PAGES
monatomic ions. However, many common ionic substances contain polyatomic ions, which are
held together by covalent bonding. Moreover, some ionic substances, known as hydrates, actually
contain water molecules within their formulas. In this section, we examine the chemical species
191
S E C T I O N 6.1 The Octet Rule
that are held together by a combination of ionic and covalent bonding.

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190

Figure 6.1

CHAPTER 6

Representing Molecules

The Properties of Atoms

Polyatomic Ions
Metals, such as sodium, easily lose one
or more electrons to become cations.

Na

1s22s22p63s1
IE1 = 496 kJ/mol
EA = +52.9 kJ/mol
r = 186 pm

sodium chloride.

NaCl

Nonmetals, such as chlorine, easily gain
one or more electrons to become anions.

Cl

Ions that consist of a combination of two or more atoms are called polyatomic ions. Because these
ions are commonly encountered in general chemistry, you must know the names, formulas, and
Na+
charges of the polyatomic ions listed in Table 5.10. Although most of the common polyatomic ions
are anions,