ACP Chemistry Cornerstone Activity
Nomenclature — The Ionic Compounds Puzzle
Purpose
In this experiment you will determine the ratios with which ions combine to form ionic compounds,
and to write the corresponding empirical formulas.
Introduction
Ionic compounds consist of positively charged ions (cations) and negatively charged ions (anions)
stacked together in an orderly fashion (a crystal!). The empirical formula of the ionic compound,
which is the smallest whole number ratio of the ions, depends upon the number of positive
charges in the cation, and the number of negative charges in the anion. The ions combine in a
ratio that allows all positive charges to balance all negative charges.
This activity will allow you to see the relationship of positive to negative charges in ionic
compounds, and how to write empirical formulas for ionic compounds based upon this
relationship.
Materials
Be certain that you can identify the equipment and reagents listed below, before starting the
experiment.
 scissors
 page with cation puzzle pieces
 page with anion puzzle pieces
 laboratory notebook, or the Ionic Puzzle Answer Sheet
Procedure
1. Cut out the puzzle pieces from the sheets provided. Cut them out quickly — they need
not be perfect! There are three or four of each type. Keep each type in a separate stack.
2. Arrange the stacks of cations in alphabetical order in a horizontal line on the lab bench.
3. Arrange the stacks of anions in alphabetical order in a horizontal line on the lab bench.
4. Work through the formulas in the data section, below (or on the answer sheet.) Model the
charge balancing by placing the puzzle pieces together such that each positive charge
(+) from a cation neighbors a negative charge (-) from an anion. You may need more
than one cation and/or anion to achieve this. Every completed ionic compound puzzle will
be a rectangle, if you correctly balance charges.
5. Write the formula for each ionic compound by writing the formula for the cation, leaving
out the charge, and writing a subscript for the number of cations required for the model,
and writing the formula for the anion, leaving out the charge, and writing a subscript for
the number of anions required in the model. Use parentheses for polyatomic ions if more
than one is needed.
Pre-activity Assignment
Answer the following pre-activity questions. Record your answers in your laboratory notebook or
on a blank piece of notebook paper, according to the instructions from your teacher
1. What is an ion?
2. What makes an ion a cation?
3. What makes an ion an anion? (Isn't that a mouthful to say!)
4. What is an empirical formula?
Activity
Part A. Use the ion puzzle pieces to make each of the compounds in the 5 x 5 matrix. Examine
the relationship of the number of puzzle pieces of each ion type and how the empirical formula is
written. Pay particular attention to the subscripts in the empirical formulas. In each box, write the
compound name and the empirical formula.
Part A.
anions Ffluoride
O2oxide
N3nitride
NO3 nitrate
SO3 2sulfite
cations
Na+
sodium
Al3+
aluminum
Pb4+
lead (IV)
Pb2+
lead (II)
NH4+
ammonium
Part B. Given the names and empirical formulas in the matrix, fill in all of the blank boxes, including ions.
Part B.
anions
cations
KCl
potassium chloride
Ca(C2H3O2)2
calcium acetate
Fe(OH)3
iron (III) hydroxide
FeSO4
iron (II) sulfate
Cu3PO4
copper (I) phosphate
Post-activity Questions
Answer the following questions in your lab notebook or on a separate sheet of paper.
1. What is a monatomic ion? Give three examples.
2. What is a polyatomic ion? Give three examples.
3. What makes ionic compounds charge neutral?
4. What type of solids do ionic compounds make?
5. Why do ionic compounds have empirical formulas and not molecular formulas?
6. Do you expect lead (II) chloride and lead(IV) chloride to have the same chemical
properties? Explain.