How to spot ionic compounds
Students often struggle to identify types of compounds and name them appropriately. The first step is to identify if a compound is primarily ionic or covalent. Ionic compounds are often solid with crystalline forms. Covalent compounds on the other hand, can be gases, liquids, or solids and the solid state may or may not be crystalline. That’s not very concrete. The periodic table is a help. For the second step, locate the elements on the periodic table. Ionic compounds are generally comprised of a metal (cation) and nonmetal (anion) so locating the elements position on the periodic table is helpful. If the elements in the compound are on opposite sides of the stair-step line, it is likely the compound is ionic. If the elements in the compound are located very close together on the periodic table or are both on the right side of the stair-step line, the chances are the compound is covalent. Once bond type is decided, the appropriate set of nomenclature rules can be followed to name the compound correctly.
Here are 2 simple activities that help.
In the first activity, students work in small groups to combine ion cards and to name the resulting ionic compounds. Then, for a real-world connection to their card practice, students research the main ingredient in each of several common household products and identify the compound as binary or ternary. These activities are appropriate for a class of 30 high school students working in groups of 4-6 students and later in pairs.
Next Generation Science Standards
Grades 9—12
Physical Science- Chemistry
Matter and its Interactions
Materials
- 30 Index Cards
- Pen
- Timer
Preparation and procedure
- Gather the materials needed.
- On each of 10 index cards, write the symbol and charge for a different metal. Likewise, create 10 nonmetal cards, and 10 polyatomic ion cards. If you decide to include any transition metals, make sure that students are familiar with the rule of using Roman numerals as a part of the compound name to indicate the charge of the cation formed by the transition metal, e.g., copper(II) sulfate.
- Set up 5 lab stations in your classroom so that the groups can rotate.
- At each station, place 6 cards: 2 metals, 2 nonmetals, and 2 polyatomic ions.
- Divide your class into 5 groups. The class rotates through the stations, spending about 10 min at each.
- While at a station, each student picks a card and pairs with another student in the group to create an ionic compound. The group creates as many compounds as possible using the cards available at the station.
- As they create ionic compounds, students fill in a data table like the one below. Some compounds will be binary, and some, ternary. (Binary compounds consist of 2 elements, and ternary compounds consist of 3.)
- For the second activity, divide the groups into pairs. Students then research and determine the main ingredient in each of the following common household products: caustic drain cleaner, antacid tablets, table salt, baking soda, and bleach. Afterwards, they should record these ingredients’ chemical names, write their chemical formulas, and identify them as binary or ternary.
Generating Explanations
Have students take several examples of the compounds from their list and draw Lewis structures to show how electrons are being transferred. They may then create 3-D models of the structures like the one of common table salt seen here.
For additional practice, students can take several examples of the compounds from their list and draw Lewis structures to show how electrons are being transferred. They may then create 3-D models of the structures.
For additional practice students can identify bond type with lab tests in our Chemical Bonding Kit and investigate structure further with Molymod molecular model sets. Establishing the connections among location on the periodic table, the compound’s physical and chemical properties, the shape of the compound, the compound name and formula make putting together the chemistry puzzle pieces much easier.
