Materials Included In Kit

Prelab Preparation

1. Remove one card from each set. You may want to remove a different card for each group. Suggested cards are Blue 11.7; Yellow 13.8, 34.0 or 42.1; Pink 24.7 or 36.2; Green 16.7; White 48.4; and Lavender 19.5 or 29.3. Do not remove Green 38.7 or White 37.0. These cards represent the sequencing problem that was incurred by arranging the elements according to atomic mass.
2. Shuffle each set separately.

Lab Hints

• Enough materials are provided in this kit for 30 students working in teams of 3 or for 10 groups of students. This activity can reasonably be completed in one 45- to 50-minute class period. The prelaboratory assignment may be completed before coming to lab. The post-lab questions and analysis should be completed while the students still have the cards arranged.
• Students should have a basic understanding of atomic structure, elements, atomic mass and atomic number.
• Each set of cards may be kept in an envelope marked with a group number to aid in keeping track of the cards as they are returned by each group.
• Make a list of group numbers and which card is pulled from each corresponding set for easy reference when checking each group’s prediction of the missing card and for returning the cards to the correct sets.

Teacher Tips

• This is a great activity to introduce the history and arrangement of the periodic table as well as understanding the nature of science.
• The inconsistency of the green 38.7 and the white 37.0 cards represents the dilemma with arranging the elements by atomic mass. Ask students to look at a modern periodic table and find similar examples (elements 18 and 19, 27 and 28, and 52 and 53). Mendeleev assumed and proposed that when the family properties did not coincide with increasing atomic mass, the atomic masses were in error. Atomic numbers (the number of protons) were not known at the time.
• To reinforce the importance of family properties, focus on elements 18 and 19. Discuss with students the inconsistencies with the arrangement if argon, a noble gas, and potassium, a highly reactive alkali metal, were placed in the periodic table according to their corresponding atomic masses.
• Be careful to not take the analogy between the cards in the activity and the elements in the periodic table too far. The numbers do not represent atomic masses of actual elements. The focus should be on classification, discovering patterns and trends, and problem-solving.
• Keeping in mind the spirit of discovery, remind students that there is no single correct answer for the arrangement of the cards. Mendeleev’s first published table of the elements (1869) had the elements listed in order of increasing atomic mass in columns, so similar family properties were found in horizontal rows. The vertical arrangement of families appeared two years later, in 1871. The important thing to remember is students must be able to justify their arrangements.
• Students can recreate the excitement that followed the prediction and discovery of one of Medeleev’s missing elements—germanium—with “Density Is a Periodic Property” Super Value Kit, available from Flinn Scientific (Catalog No. AP6268).

Answers to Prelab Questions

1. Define classification.

   Classification is a method of arranging or organizing components of a group according to common characteristics.

2. Describe an everyday example of two-dimensional classification not mentioned in the Introduction or Background sections.

   Organizing music CDs by type and alphabetically, books by genre and alphabetical by author, clothes by type (e.g., pants, shirts, socks) and color.

3. Why is it helpful to classify the elements?

   By classifying the elements, investigating and keeping track of characteristics becomes easier, reasonable predictions can be made, and better models for explanations can be developed.

Sample Data

1. Describe the characteristics of the cards. How are they alike? How are they different?

   Each card has a number that includes one digit to the right of the decimal (tenths). Each card is one of six different colors. All the cards are the same rectangular shape and size.

2. What property did you use to arrange the cards in one long row?

   The cards were arranged according to increasing numerical value.

3. Describe the two-dimensional classification of your final arrangement in the following manner. a) How are the cards arranged in each row? b) What property do the cards in a column have in common? c) What exceptions to the pattern, if any, are found in your arrangement?

   a) In each row, the numerical value of the cards increases from left to right. b) All the cards in a column have the same color. The numerical value of the cards in a column increases roughly by 10 from one row to the next. c) In row four, two numbers, 38.7 and 37.0, are not in sequence according to increasing numeric value.

4. Predict the properties (number and color) of the missing card. Give reasons for your prediction.

   Students should be able to predict the color of the missing card and give a reasonable estimate of the number. Example: If the yellow card 34.0 is “missing” from the deck, the number on the card can be estimated two ways—as the average of either the two cards above and below it in sequence or the cards to the left and right of it.

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Answers to Questions

5. What property or properties of the cards in the final arrangement show a repeating or periodic pattern?

   The sequence of colors—blue, yellow, pink, green, white and lavender—repeats with each new row.

6. Elements in each column in the periodic table are known as a family and rows are called periods. Would these names also be appropriate for your arrangement of cards? Explain.

   These names would also be appropriate for the arrangement of the cards. Members of the same family often have common characteristics. Each column of cards has the common characteristic of color. Period is a good description for each row since the color pattern is repeating, or periodic.

7. Elements in the first column of the periodic table belong to the alkali metal family. Name the alkali metals and describe two chemical properties that the alkali metals share.

   The alkali metals are lithium, sodium, potassium, rubidium, cesium and francium. Alkali metals have one outer energy level electron, are highly reactive, and have low melting points and densities. Note: Hydrogen, although often placed at the top of the first column, is not included with the alkali metals.

8. Mendeleev arranged the elements in order of increasing atomic mass. Today the elements are arranged in order of increasing atomic number (number of protons), a property not known during Mendeleev’s time. Based on your results, give a possible explanation why this was a better method.

   If the cards were arranged by increasing numeric value, two cards would be out of place according to the property of color. Arranging the elements by atomic number instead of atomic mass allowed the elements with common family properties to be appropriately placed. (See elements 18 and 19, 27 and 28, and 52 and 53.)

References

Special thanks to Fran Zakutansky, Pascack Valley High School, Hillsdale, NJ, for sharing this activity with Flinn Scientific.

Introduction

Have you ever gone to a video store to find a particular movie? The videos are arranged, or classified, according to type, as well as alphabetically. This arrangement is an example of two-dimensional classification. All the videos in a particular section have something in common and are arranged A to Z. When you come to a different section, the alphabetical arrangement is repeated. Experience for yourself how a method of two-dimensional classification led to the modern-day arrangement of the elements known as the periodic table.

Concepts

• Patterns and trends
• Periodic table
• Two-dimensional classification

Background

In the years 1868–1870, Dmitri Mendeleev (1834– 1907), a professor of chemistry at the University of St. Petersburg in Russia, was writing a new textbook called Principles of Chemistry. More than 60 individual elements were known, along with a great many facts about their properties. Mendeleev knew the atomic masses of the elements, their densities, boiling points, and melting points. What was missing was a way to organize these facts, a way to understand how individual facts related to each other—in short, a way to classify the elements. The following quote from Mendeleev reveals his thoughts at the time:

“I wished to establish some sort of system of elements in which their distribution is not guided by chance... but by some sort of definite and exact principle.”

Mendeleev decided to arrange the elements according to atomic mass. He wrote out the exact atomic masses (as they were known at the time) in the margin of a list of the elements, and then wrote out separate cards for each of the elements with the atomic mass and other chemical and physical properties. Using these cards, Mendeleev played “chemical solitaire” for several hours, finally copying to a sheet of paper the arrangement he had worked out with the cards. With slight modification, this became Mendeleev’s first Periodic Table of the Elements. Periodic refers to the repeating pattern of certain properties of the elements when properly arranged. This organization of the elements into a logical table is perhaps one of the greatest achievements in the history of science. Other chemists had developed tables of the elements, but Mendeleev’s table was different because he left gaps for several elements yet to be found based on the patterns and trends he discovered. He even accurately predicted the properties of these missing elements!

Experiment Overview

The purpose of this activity is to arrange a set of 29 out of 30 numbered cards of different colors in rows and columns that will display certain patterns and trends. Students will then predict the number and color of the missing card. 

Materials

Prelab Questions

1. Define classification.
2. Describe an everyday example of two-dimensional classification not mentioned in the Introduction or Background sections.
3. Why is it helpful to classify the elements?

Procedure

1. Look through the set of cards. Write a general description of the characteristics or properties of the cards in the Observations section on the Periodic Table Analogy Worksheet.
2. Place all the cards in a logical sequence in one long row. Describe the property of the cards you used to do this on the worksheet.
3. Keeping the cards in the same order from step 2, arrange the cards in several rows so the each card in a column has a common property with the other cards in the same column. In other words, decide where to break the original arrangement to begin each new row so a pattern results.
4. It may be impossible to keep the cards in the same original order and have all the cards in a column with a common property. Discuss which property is more appropriate for classifying the cards—the property used to sequence the cards in a row, or the common property of the cards in a column. Arrange the cards appropriately.
5. Once the group has finalized the arrangement of cards, describe the resulting two-dimensional classification system on the worksheet, and note any exceptions to the pattern.
6. One card is missing. Predict the properties (color and number) of the missing card on the worksheet.
7. Answer the Post-Lab Questions and Analysis.
8. Return the cards as instructed by the teacher.

Student Worksheet PDF

12703_Student1.pdf