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# Experiment Naming Ionic and Molecular Compounds

Note that permanganate, chromate, and dichromate each have a metal and a nonmetal.

Note: There are additional tables of polyatomic ions available online and in textbooks. This table includes only the most common ions encountered in general chemistry classes.

Here are a few helpful hints for naming polyatomic ions:

a. Suffixes: the name of the ion usually ends in “-ite” or “-ate.” A low oxidation state will have an ion ending in “-ite,” versus a higher oxidation state that ends in “-ate.” The oxidation state is dependent upon a calculation of the charges of the polyatomic ion. Figure 5 shows the calculations of the oxidation state for the sulfite ion (SO3

2-) and the sulfate ion (SO4

2-). A simple algebraic calculation is done to determine the oxidation state for each polyatomic ion by solving for “x” since we know that oxygen (O) carries a 2- charge:

Experiment Naming Ionic and Molecular Compounds

Figure 5. Algebraic calculations for the oxidation state of the polyatomic ions sulfite and sulfate.

b. Prefixes: “hypo-” indicates the very lowest oxidation state and “per-” indicates the very highest oxidation state. Figure 6 shows the calculations of the oxidation state for the hypochlorite ion (ClO-) and the perchlorate ion (ClO4

-). A simple algebraic calculation is done to determine the oxidation state for each polyatomic ion by solving for “x” since we know that oxygen (O) carries a 2- charge:

Figure 6. Algebraic calculations for the oxidation state of the polyatomic ions hypochlorite and perchlorate.

Experiment Naming Ionic and Molecular Compounds

c. Few polyatomic ions have positive charges. These ions have names ending in “-onium.” For example, ammonium (NH4

+) and hydronium (H3O +).

d. There are a few exceptions to these rules. The following polyatomic ions were once thought to be monatomic ions so they end in “-ide:” hydroxide (OH-), cyanide (CN-), and peroxide (O2

2-).

Naming Polyatomic Ion Compounds

Example 9: Writing a Metal + Polyatomic Ion Name: KNO2 1. Read the formula and look at the subscripts.

KNO2 2. Determine if the metal ion has a fixed charge or variable charge.

K = Group IA = fixed charge = 1+

3. Record the entire name of the cation.

K = potassium

4. Record the entire name of the anion.

NO2 = nitrite

5. Write the name of the ionic compound.

potassium nitrite

Example 10: Writing a Metal + Polyatomic Ion Formula: Gold(I) Nitrate