Using a Gallery Walk inquiry activity to guide students through naming binary ionic compounds with variable charges

example slide comparing copper I chloride and copper II chloride

While students usually do well with naming binary ionic compounds of fixed charge, many students struggle with naming ionic compounds that contain ions of variable charge. Common mistakes include:

  • Failing to indicate charge using a Roman numeral
  • Thinking that the Roman numeral indicates the number of atoms instead of the charge
  • Failing to notice the differences in two compounds that vary only by differing charge
  • Not understanding how the combination of the same two elements can lead to two different formulas
  • Not realizing that two compounds that contain the same atoms but have different formulas can have very different properties

To address these misconceptions, I designed a gallery walk to introduce students to the concept of ionic compounds that contain cations of variable charges. Students may have previously seen some examples of compounds that are formed with these elements, but have not been taught the rules for naming them. They have been taught and have extensively practiced forming and naming binary ionic compounds of fixed charge, so they are familiar with the general rules of naming ionic compounds (name the cation first, the anion ends in –ide) as well as the idea of balanced charge in ionic compounds.

A gallery walk is an activity in which students explore multiple images or texts that are placed around the room. As they walk around, they make observations. This activity was designed as a digital gallery walk, but it can also be printed out and used in the traditional format with students writing observations as they move through the “gallery”. During the activity, students explore names, formulas, images and sometimes extra information about related compounds. As they progress through the gallery, students are prompted to make specific observations and compare and contrast the compounds. I did this as a  activity (a Google Slides add-on that allows teachers to see student responses to questions in real time), but it could also be done with a different program (such as – another digital program that allows teachers to review student work in real time or even screen monitoring programs). A digital whiteboard program such as would also be another option to present this activity, but this method would allow all students to see each other’s observations, which may change the way the students engage with the exploration. One of the particular strengths of this activity is the discussion that occurs as the teacher can see the real-time student responses, but if this is not possible then students would probably benefit from seeing each other’s responses, as they do in a gallery activity where they make observations and leave them at each image on a sticky note.


example slide from activity, comparing platinum II chloride and platinum iV oxide

Figure 1: Slide #3 compares platinum II chloride and platinum IV oxide.


By the end of the activity, students should self-discover the meaning of the names and the rules that guide them:

  • Roman numerals are used to indicate charge
  • The charge on the anion and number of anions must be used to determine the charge on the cation

Students also discover several facts about various compounds of the same elements:

  • Charge on the cation can change the color of the compound
  • Different compounds have different properties, including reactivity and toxicity


Figure 2: Slide #7 shows four colorful solids containing chromium with different charges.


The activity begins with a simple comparison of two compounds, increasing in information on each slide and leading student through the discovery process (see figures 1 & 2 for examples). The slides are also intentionally designed to address common misconceptions as students move through the activity (see Table 1). 


Table 1: Concepts addressed




Slide 2

PbS and PbS2

  • Students compare two compounds that only differ in the subscript of the anion
  • Introduces students to the idea of two possible formulas for the same set of ions

Slide 3

PtCl2 and PtO2

  • Students compare two compounds that have the same cation and same anion subscript, but have different roman numerals in the name
  • Shows two formulas of the same subscripts but different charge

Slide 4

FeO and Fe2O3

  • Students compare two compounds of the same elements that have different subscripts
  • Unit cells models for each are shown, as is the name of the mineral and a picture of solid sample of each
  • Students visually see a difference in the solids, and compare the different cations of iron

Slide 5

Hg2Cl2 and HgCl2

  • Students compare two compounds of the same elements that have different subscripts
  • Toxicity of each compound is compared, as well as a historical application
  • Students are asked what chemical formula is unique to identify the exception for mercury(I), which brings the conversation back to a reminder of the general rules of writing ionic formulas

Slide 6

CuCl and CuCl2

  • Students compare two compounds of the same elements that have different subscripts
  • Students label the charges in each compound, and visually see a difference in color between the two

Slide 7

CrO3, CrCl3, CrO2and Na2CrO4

  • Students compare different compounds of chromium
  • Students identify the charges of the cations, and while they are not asked about the chromium ion, it does begin to introduce the concept/existence of polyatomic ions

Slide 8

SnCl2 and SnCl4

  • Check for understanding of names to formula
  • Students examine images of two reagent bottles
  • Shows importance of reading reagent bottles very carefully

Slide 9

Cr2O3, TiO2, Sb2O3, CdS, CdSe

  • Final slide checks for understanding of formula to name
  • Shows application of various compounds (pigment in paint)


It took about 30 minutes for my students to work through in Pear Deck. After this activity, we transitioned into a traditional practice of ionic naming with students being asked to give names or formulas for the corresponding given information.

In previous years in which material was presented via direct instruction, students really struggled with the meaning and purpose of Roman numerals in ionic nomenclature. After using this activity to allow students to self-discover the purpose and meaning behind the numerals, comprehension was greatly increased and mastered more quickly. This was accomplished by having students do the thinking through higher order tasks (comparisons, predictions) and guiding questions. Students were much more engaged in the activity than they were during a traditional lesson and the side conversations regarding application of the different compounds was engaging for both the students and the teacher. This activity also has the opportunity for extension by having students find their own pairs of related compounds. Ultimately, an activity in which a student is actively engaged will always net greater gains across the board, and this introduction to ions of variable charge provides just such an opportunity.


Access the Google Slides: 

Thank you to Thomas Jankowski for his review and suggestions during the creation of this activity.