Writing Formulas For Ionic Compounds Practice

Stephanie O'Brien | Tue, 12/01/2020 - 11:52

Writing formulas is one of those concepts in chemistry that requires much practice and repetition for students to gain confidence. Some issues students find challenging when learning to write formulas are identifying when a roman number is needed and what the value of that numeral should be, how and when to use prefixes, when are parentheses needed and what the suffix of a compound name should be.

In a non COVID world, to help students practice writing formulas, I would have students complete an activity where they roll two dice, one with a variety of cations on it and another with various anions on it. The goal was to combine the two dice to create an ionic compound. Students would then write the formula for the ionic compound and the corresponding name. It was a fun way for students to practice formula writing yet wasn't daunting or seem as boring to a student as a worksheet full of practice questions. This year due to restrictions in sharing lab materials a digital alternative was needed. Jessica Mintz (@mintzchemistry) has created a version of the activity that will work in a remote world. The lesson should take about forty minutes.

Download a copy of the following procedure to your Google Drive:Names and Formulas Activity Google Doc

If you use Google Classroom, create a copy for every student when you assign the activity. If you do not use Google Classroom, you canforce a copy for students.

Materials:

Share the Google Doc with students.

Procedure:

Figure 1: TeacherLed.com's dice option

Students will roll dice virtually using a website for digital dice. They need to choose the pink and blue dice from the menu at the top of the screen to match the colors in the Dice Key. After each roll they will match the values of the dice to the key and record the cation and anion in the table provided (see figure 4). They will consider the ratio of ions and write the chemical formula. (They can use SymbolSalad.com for subscripts and superscripts.) Then students will record the name of the compound. An example is provided in the Google Doc. Students need to record 10 different chemical formulas using the dice.

Figure 2: Example showing how to determine the subscripts when considering the ratio of ions required to achieve a neutral charge.

Figure 3: Data table for recording results

Questions:

The following questions are included in Google Doc of the activity as referenced above.

Explain, in terms of electrons, what a positive ion indicates.
Explain, in terms of electrons, what a negative ion indicates.
Explain why ionic compounds are "fixed" in their chemical composition.
Why do some ionic compounds contain a roman numeral?
If element X combines with oxygen to form an ionic compound X₂O , what is the charge of element X? What Group does X belong to on the Periodic Table?

Preparation:

Provide students access to the activity Google Doc noted above.

Credits:

This activity uses the TeacherLed.com Dice option (https://www.teacherled.com/iresources/tools/dice/). It also uses the SymbolSalad.com created by @KevPluck (https://symbolsalad.com/).

Attribution:

Thanks to Jessica Mintz (@mintzchemistry) for revising my Names and Formulas dice activity into a virtual activity.