Why that Formula?

Pre-Lab Questions

1. Which of the following are monoatomic ions?

Na+1 , OH-1 , Cl-1 , Ca+2 , CO3-2 , SO4-2

2. Which of the following are polyatomic ions?

Na+1 , OH-1 , Cl-1 , Ca+2 , CO3-2 , SO4-2

3. Based on your answers to questions 1 & 2, define

  1. monoatomic ion ______
  1. polyatomic ion ______

Oxidation numbers and the charges of ions give the information needed to write the formulas of many chemical compounds. Only a few guidelines are needed.

  1. In a neutral compound, the charges on ions, of the oxidation numbers, balance out to zero.
  2. One positive charge balances one negative charge.
  3. Ions with positive charges or positive oxidation numbers are written first.
  4. Subscripts show the relative numbers of atoms or ions in a compound.
  5. To show more than one of a polyatomic ion, the symbol is enclosed in parentheses and the subscript follows; for example, Al2(SO4)3.

In this activity you will use paper models to show how chemical formulas are derived from oxidation numbers.

Procedure

  1. Cut out each of the ion squares on your sheet of ion models
  2. Assemble the ion models for six compounds containing the following pairs of ions:
  3. nickel (II) and iodide
  4. nickel (III) and chlorite
  5. zinc and oxide
  6. copper (I) and sulfide
  7. nickel (III) and chlorate
  8. tin (II) and sulfite
  9. copper (II) and iodide
  10. tin( IV)and sulfide
  11. nickel (III) and oxide
  12. copper (II) and sulfite
  13. zinc and hydrogen sulfite
  14. Glue your compound combinations on a sheet of white paper. There must be an equal number of positive and negatives in each compound. This means that some compounds will consist of more than 2 ion squares.
  15. Make a Data Table with the headings “Combining Ions,” “Chemical Formula,” and “Name of Compound.”
  16. Complete the table using the six compounds you made in Step 2.

Analysis

  1. Some compounds are described as “binary compounds.” What does this mean? List the formulas and names of any binary compounds you have constructed.
  2. Which elements on your list form ions with two different oxidation numbers?
  3. Parentheses must be used to show more than one of a polyatomic ion. List the formulas of any compounds on your list where this was necessary.
  4. If the charges on both the ions in compound are of the same magnitude and opposite sign, + or -, did the formula for the compound contain subscripts? Give and example.
  5. Is their a relationship among the subscripts and charges of compounds that do not have charges of the same magnitude but have opposite signs, + or -.
  6. Some elements have more than one oxidation number. To show the oxidation number of such elements in a compound, a Roman numeral is given in the name of the compound. Give names for the following compounds.
  7. UF6
  8. UF5
  9. PbCl2
  10. PbCl4
  11. Describe in complete sentences how you can determine the formula, for a compound, without the use of the ion square.

Grading RubricName______

______Title

______Purpose

Pre-Lab Questions

______#1

______#2

______#3a

______#3b

______Procedure Summary

______Data Table

______Compound models on white paper

Analysis

______#1

______#2

______#3

______#4

______#5

______#6

Glossary

______monoatomic ion

______polyatomic ion