PRINCHEM LAB 1.1

The names and chemical formulas of compounds are essential vocabulary in chemistry.

The system used in naming substances is called chemical nomenclature, from the

Latin words nomen (name) and calare (to call).

There are more than 50 million known chemical substances. Naming them all

would be a hopelessly complicated task if each had a name independent of all others.

Many important substances that have been known for a long time, such as water (H2O)

and ammonia (NH3), do have traditional names (called common names). For most substances, however, we rely on a set of rules that leads to an informative and unique name

for each substance, a name based on the composition of the substance.

The rules for chemical nomenclature are based on the division of substances into

categories. The major division is between organic and inorganic compounds. Organic

compounds contain carbon and hydrogen, often in combination with oxygen, nitrogen,

or other elements. All others are inorganic compounds. Early chemists associated organic

compounds with plants and animals and inorganic compounds with the nonliving portion of our world. Although this distinction is no longer pertinent, the classification between organic and inorganic compounds continues to be useful. In this section we

consider the basic rules for naming three categories of inorganic compounds: ionic

compounds, molecular compounds, and acids.

Names and Formulas of Ionic Compounds

Recall from Section 2.7 that ionic compounds usually consist of metal ions combined with

nonmetal ions. The metals form the cations, and the nonmetals form the anions.

1. Cations

a. Cations formed from metal atoms have the same name as the metal:

CO3

2- Fe3+ SO4

2- Zn2+ PO4

3- Na+

NO3

- Mg2+ NO -

3

Na+ sodium ion Zn2+ zinc ion Al3+ aluminum ion

Fe iron(II) ion 2+ Cu copper(I) ion +

Fe iron(III) ion 3+ Cu copper(II) ion 2+

b. If a metal can form cations with different charges, the positive charge is indicated by

a Roman numeral in parentheses following the name of the metal:

Ions of the same element that have different charges have different properties,

such as different colors ( FIGURE 2.23).

Most metals that form cations with different charges are transition metals,

elements that occur in the middle of the periodic table, from group 3B to group

2B. The metals that form only one cation (only one possible charge) are those of

group 1A and group 2A, as well as (group 3A) and two transition-metal

ions: (group 1B) and (group 2B). Charges are not expressed when

naming these ions. However, if there is any doubt in your mind whether a metal

forms more than one cation, use a Roman numeral to indicate the charge. It is

never wrong to do so, even though it may be unnecessary.

Zn2+ Ag+

Al3+

 FIGURE 2.23 Different ions of the

same element have different properties.

Both substances shown are compounds of

iron. The substance on the left is Fe3O4,

which contains Fe2+ and Fe3+ ions. The

substance on the right is Fe2O3, which

contains Fe3+ ions.

60 CHAPTER 2 Atoms, Molecules, and Ions

An older method still widely used for distinguishing between differently

charged ions of a metal uses the endings -ous and -ic added to the root of the

element’s Latin name:

Fe ferrous ion 2+ Cu cuprous ion +

Fe ferric ion 3+ Cu cupric ion 2+

Although we will only rarely use these older names in this text, you might

encounter them elsewhere.

c. Cations formed from nonmetal atoms have names that end in -ium:

NH4 ammonium ion + H3O hydronium ion +

These two ions are the only ions of this kind that we will encounter frequently in

the text.

The names and formulas of some common cations are shown in TABLE 2.4

and on the back inside cover of the text. The ions on the left side in Table 2.4 are

the monatomic ions that do not have more than one possible charge. Those on

the right side are either polyatomic cations or cations with more than one possible charge. The ion is unusual because, even though it is a metal ion, it is

not monatomic. It is called the mercury(I) ion because it can be thought of

as two ions bound together. The cations that you will encounter most

frequently are shown in boldface. You should learn these cations first.

GIVE IT SOME THOUGHT

a. Why is CrO named using a Roman numeral, chromium(II) oxide, whereas CaO

is named without a Roman numeral, calcium oxide?

b. What does the -ium ending on the name ammonium ion tell you about the

composition of the ion?

Hg+

Hg2

2+

TABLE 2.4 • Common Cations*

Charge Formula Name Formula Name

1+ H hydrogen ion NH4

ammonium ion

Li+ lithium ion Cu+ copper(I) or cuprous ion

Na sodium ion

K potassium ion

Cs+ cesium ion

Ag silver ion

2+ Mg2 magnesium ion Co2+ cobalt(II) or cobaltous ion

Ca2 calcium ion Cu2 copper(II) or cupric ion

Sr2+ strontium ion Fe2 iron(II) or ferrous ion

Ba2+ barium ion Mn2+ manganese(II) or manganous ion

Zn2 zinc ion Hg2

2+ mercury(I) or mercurous ion

Cd2+ cadmium ion Hg2 mercury(II) or mercuric ion

Ni2+ nickel(II) or nickelous ion

Pb2 lead(II) or plumbous ion

Sn2+ tin(II) or stannous ion

3+ Al3 aluminum ion Cr3+ chromium(III) or chromic ion

Fe3 iron(III) or ferric ion

*The ions we use most often in this course are in boldface. Learn them first.