Materials Included In Kit

Additional Materials Required

Safety Precautions

This laboratory activity is considered nonhazardous. Remind students to exercise caution when working with scissors.

Disposal

Cards may be stored for future use.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs. This activity can reasonably be completed in one 45- to 50- minute class period. The prelaboratory assignment may be completed before coming to the lab. The postlab questions and analysis should be completed after class.
• Students should have a basic understanding of atomic structure, elements, atomic mass and atomic number.
• Once each group cuts their element card sheet into individual cards, each set of cards may be kept in an envelope with a group number. Makes keeping track of the cards and ensuring their complete return easier.

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.
• Students can recreate the excitement that followed the prediction and discovery of one of Mendeleev’s missing elements—geranium—with “Density Is a Periodic Property” Super Value Kit, available from Flinn Scientific (Catalog No. AP6268).

Answers to Prelab Questions

Sample Data

Students should arrange their cards in the following order. Realize that GBA or GAB are both logical arrangements for period three.

Answers to Questions

1. What characteristics in the element square you constructed are periodic?

   All characteristics are periodic of the value of the trait in the squares of a period all show incremental change and the family squares are constant in the same trait.

2. Do the weights of the elements in each family change by roughly the same amount as you go down the row? Is weight periodic?

   Yes, weights of the elements in each family do change by roughly the same amount as you go down a family. No, weight is not periodic. For example, weight does not increase from Te (tellurium) to I (iodine)

3. Refer to the periodic table you constructed, is the change in weight between elements periodic?

   No, the present day periodic table is not periodic with respect to weight. If the weight is periodic then the atomic number is not and vice versa.

4. How does the periodic table used today differ from the earlier versions, in particular Mendeleev?

   Mendeleev’s original periodic table was periodic in respect to weight. Modern periodic tables are not classified by weight.

5. Based on your results, give a possible explanation why modern day periodic tables are organized differently than Mendeleev’s original periodic table?

   Arranging the elements by atomic number instead of atomic mass allowed the elements with common family properties to be appropriately placed.

References

Special thanks to Dr. Tim Schaap, Retired, Elk Grove High School, Elk Grove, IL, for sharing this activity with—providing the idea and the instructions for this activity to Flinn Scientific.

Kauffman. 1969. American Forerunners of the Periodic Chart. J. Chem. Ed, 46, p 128.

Rignes et al. 1989. Discovering the Periodic Table. J. Chem. Ed, 69, p 701.

Wolfenden. 1969. The Noble Gases and The Periodic Table. J. Chem. Ed, 46, p 569.

Introduction

Have you ever gone to the video store and looked for a specific 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 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

• Periodic table
• Period vs. family
• 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. A horizontal row of elements on the periodic table is known as a period. Family is a concept of “same.” Families are present in vertical columns; so that each element has the same value. Scientists originally thought that weight was a family concept, even though the weights were not the same for every element. They found if you added the top and bottom element weight in a family and divided it by two, it always gave the weight of the element in the middle of that column. 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 nine elements from the periodic table without their name or atomic number.

Materials

Prelab Questions

1. Identify the meaning of every letter of number in the potassium box located below. Use a chemical handbook for help if necessary.
   {14129_PreLab_Figure_1}

Safety Precautions

This laboratory activity is considered nonhazardous. Please follow all laboratory safety guidelines.

Procedure

1. Your instructor will give each lab group a sheet containing nine elements from the periodic table without their name or atomic number.
2. Using scissors, cut along the dotted lines resulting in nine element cards.
3. Arrange these nine elements into three rows and three columns according to the definition of periodic and family found in the background section.
4. Each element lists characteristics of weight, density, boiling point, melting point, valences, number of isotopes and number of radioactive isotopes. Determine which characteristics are periodic and which are constant. Note: Constant changes may occur if you add the characteristics in the top and bottom element of a family and divide by to yield the property of the middle element.

Student Worksheet PDF

14129_Student1.pdf