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ACTIVITY in Periodic Table, Identifying an Unknown. Last updated March 25, 2020.


In this activity, students learn about periodic trends by organizing cards and then determining the information on a missing card.

Grade Level

High school


By the end of this lesson, students should be able to

  • Understand why the periodic table is organized the way it is.
  • Understand that trends on the periodic table exist.

Chemistry Topics

This lesson supports students’ understanding of

  • the periodic table
  • periodic trends


Teacher Preparation: 10 minutes

Lesson: 15 minutes


  • A set of cards (see "Downloads" Student Activity Cards.pdf)


  • No specific safety precautions are needed to be observed for this activity.

Teacher Notes

  1. Print out enough sets of cards so that students may work in pairs. A set is all nine cards, individually cut.
  2. Give each group a set of cards and ask them to not look at the cards. Shuffle and remove one card faced down so that they do not know what is on the missing card.
  3. Ask the students to now look at the remaining cards and figure out the pattern that will allow them to determine the information on the missing card (color of dot, color and number of stars, top number, and bottom number).
  4. Tell students that not all of the information contained on the card follows a pattern, but most of the patterns can be seen in rows and columns.
  5. Students should be given about 10 minutes to manipulate the cards and determine the information on the missing card as you move about the room assisting and checking results by comparing their guesses to the missing card.
  6. After checking each group’s answers, you can discuss how Mendeleev used this method to arrange elements on the periodic table and use this analogy to explain how he was able to accurately predict the properties of the then undiscovered element germanium.
  7. Assessment: Have students write a description of how well they were able to determine the information on the missing card. Have them explain how the periodic table may be used to predict properties of unknown elements.