The Foundations of Chemistry

IONS AND IONIC COMPOUNDS

So far we have discussed only compounds that exist as discrete molecules. Some com-
pounds, such as sodium chloride, NaCl, consist of collections of large numbers of ions.
An ionis an atom or group of atoms that carries an electric charge. Ions that possess a
positivecharge, such as the sodium ion, Na, are called cations.Those carrying a nega-
tivecharge, such as the chloride ion, Cl, are called anions.The charge on an ion must

2-3

Figure 2-6 Formulas and models

for some molecules. Structural

formulas show the order in which

atoms are connected but do not

represent true molecular shapes.

Ball-and-stick models use balls of

different colors to represent atoms

and sticks to represent bonds; they

show the three-dimensional shapes

of molecules. Space-filling models

show the (approximate) relative sizes

of atoms and the shapes of

molecules.

2-3 Ions and Ionic Compounds 53

H 2 O, water H O H

H 2 O 2 , hydrogen HHOO

peroxide

CCl 4 , carbon

tetrachloride Cl C

Cl

Cl

Cl

C 3 H 8 , propane

C 2 H 5 OH,

ethanol

CCCH

H H H

HHH

H

CCOH

H H

HH

H

Chemical Formula Structural Formula Ball-and-Stick Model Space-Filling Model

The words “cation” (kat-i-on)

and “anion” (an-i-on) and their

relationship to cathode and anode

will be described in Chapter 21.