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Polyatomic Ions
Can a group of atoms have a charge?
Name Coursework Stamp #___
Why?
Do you know you eat a lot of “-ates”? Next time you look at a food
label, read the ingredients and you will likely find a number of
ingredients that end with “-ate,” such as sodium phosphate or
calcium carbonate. Did you ever wonder what the chemical
formulas of these ingredients look like? In this activity we will
explore polyatomic ions, which are groups of atoms that carry a
charge. These ions are found in our food ingredients, natural
waterways, and many other chemical compounds you encounter
every day.
MODEL 1-Types of Ions
1. Use Model 1 to complete the table below.
2. Consider the terms “monatomic” and “polyatomic” as they are used in Model
- Write a definition for each of these terms. It may be helpful to break the words apart (i.e., poly – atomic). Make sure your group comes to consensus.
a. Monoatomic –
b. Polyatomic—
3. What types of elements (metals or nonmetals) are shown in the polyatomic
ions in Model 1?
b. Write the chemical formula for the chlorite ion, including its
charge.
Model 2 – Common Polyatomic Ions
10. What is the only polyatomic ion that is a cation?
11. How are bicarbonate and carbonate related?
12. Predict the chemical formula and charge for the bisulfate ion.
13. How are the chromate and dichromate related?
14. Bromine forms polyatomic ions with structures similar to those of chlorine.
Using the halogens family of polyatomic ions as a model, predict the name of & formula of the BrO 4 1- ion.
15. Identify the polyatomic ion in each of these ionic compounds. Write out the
name and formula of ions including their charges. a. CaCO 3 b. Mg(OH) 2 c. NH 4 Cl
Model 3-Ternary Ionic Compounds
16. How are ternary ionic compounds in Model 3 different from binary ionic
compounds (NaCl, MgO, CaBr 2 , etc.) that you’ve seen previously? Hint: Consider the meaning of the word “ bi nary.”
17. Consider the compound calcium hydroxide in Model 3.
a. How many hydroxide ions (OH1-) are combined with a
calcium ion (Ca2+)?
b. Thinking in terms of net ionic charge, is your answer to part a the
only combination of calcium and hydroxide that should exist in nature? Explain.
21. Many of the chemical formulas in Model 3 include parentheses. Which
one of the following statements summarizes the appropriate use of parentheses in ternary ionic compounds? For the three statements that do not apply in all cases, show at least one counter example from the chemical formulas in Model 3.
- Parentheses are used around any ion that is used more than once in a formula unit.
- Parentheses are used around any polyatomic ion.
- Parentheses are used around any polyatomic ion used more than once in a formula unit.
- Parentheses are only used around polyatomic anions used more than once in a formula unit.
22. Write the chemical formulas for the following ternary ionic
compounds.
a. Calcium sulfate b. Zinc nitrate c. Lithium phosphate
d. Potassium
permanganate
e. Aluminum sulfite f. Magnesium bicarbonate
23. Name the following ternary ionic compounds.
a. BaSO 4 b. NH 4 NO 3 c. K 2 Cr 2 O 7
d. Ca(NO 3 ) 2 e. Mg(CH 3 COO) 2 f. Al 2 (CO 3 ) 3
24. If you were asked to go to the chemical storage area and
retrieve a bottle of “sulfate,” could you do so? Explain. (Assume you have permission from your teacher to go into the storage area.)
25. When asked to classify sodium acetate (NaCH 3 COO) as
either an ionic or covalent compound, Thomas responded with, “Sodium acetate is both ionic and covalent.” Explain why Thomas gave this answer (and why he is correct).
