Recognizing Ions for Reaction Prediction
In order to correctly identify types of reactions and to predict the products for a reaction it is important to be able to recognize different types of compounds. In addition, since many compounds involved in these reactions are ionic, it is vital to be able to recognize the formula and charge of the component ions in a chemical formula. This activity is meant to give students practice with these skills.
Ions come in two varieties: monatomic and polyatomic. Monatomic ions based on elements in groups 1, 2, 13, 15, 16, and 17 have predictable ion charges, based on their group membership. The charges are as follows:
You are required to memorize this pattern and to recognize that when an element is part of an ionic compound it has the charge shown in this table based on its group membership.
Other monatomic ions also exist. These ions may have one of two or more possible charges. Mainly, these ions are based on metals in groups 3 - 12 but include the metals tin (Sn), lead (Pb), and bismuth (Bi). You must be able to identify an ion by its charge, based on how it balances that charge with another ion. Remember, names for this type of ion include Roman numerals to show the charge of the ion, for ex., Fe3+ is called iron(III) ion.
Polyatomic ions make up the rest of the possible ions. In chemical formulas these ions will need parentheses if more than one of them is needed to make the compound neutral.
Ionic compounds formulas are formed from pairs of ions. The ions’s formulas are stripped of their charge and the formula shows how many of each ion is needed to form a neutral combination. Here are some example ions and the formulas of compounds they make together:
Fill in the tables for each group with the atomic symbol of the elemental form of the element and the predictably-charged ion it will form in compounds.
Take the following compounds apart into their component ions. Use the example to see how.
Example: Ca3(PO4)2 is made of three calcium ions and two phosphate ions:
3Ca2+ and 2PO43–