THE MENDELEEV PUZZLE

This curriculum module is designed to open an introductory high school chemistry course. The first activity uses samples of the chemical elements, magnets, and conductivity testers for students to develop skills in drawing conclusions--and in evaluating the usefulness of such conclusions. In the second activity, paralleling Mendeleev's assembly of a periodic table, students create their own classification scheme of elements using "element cards" (their real identities are disguised). This is an excellent opportunity to discuss the landmark historical development and the many ways to represent the periodic table. In the third, more open-ended activity, students learn introductory laboratory techniques and a specific format for recording observations -- reflecting the decades of work on elements that led to the discovery of periodicity.

Table of Contents

• Overview
  
• Activity 1: Elements and Conclusions
  
• Activity 2: Mendeleev Cards
  
• Activity 3: Chemical and Physical Changes Lab

Overview

The first activity uses samples of the chemical elements, magnets, and conductivity testers. Students are first introduced to chemical elements in order to develop the process skill of drawing conclusions and evaluating the usefulness of conclusions. Rather than recording observations of elements, students must look for similiarties and differences among the elements they observe, each group of students investigating a different physical property of the same elements. Each group produces a poster for class discussion. Then students must generate conclusions which cover two or more properties of elements . To generate as many different answers as possible, students must first write conclusions individually, then as a small group. Large group evaluation of the usefulness of a conclusion focuses on whether or not the conclusion is supported by the observed properties of the elements, and whether or not it is an observation rather than a conclusion.

The second activity uses cards on which elements are identified only by a letter meant to disguise their identities. Chemical and physical properties are listed in a format borrowed from the chemistry faculties at St. John's University and the College of St. Benedict, Collegeville, Minnesota. Students create their own classification scheme in a simulation of the process by which Dmitri Mendeleev organized information into a periodic table. Two options exist: (1) teachers can focus student inquiry toward the standard grid-type form of the periodic table, or (2) students can be encouraged to create their own classification structure. In both options, students are constantly challenged to defend the criteria they use for classifying elements into groups. In the historico-investigative method, students should repeat historical experiments to determine the physical and chemical properties of the elements before classifying their properties. Mendeleev's classification used existing data and was a theoretical rather than investigative approach. His theory did however, lead him to predict the existence and properties of undiscovered elements. Their discovery provided empirical data to support his theory. A unique approach to a hands-on method of creating a Mendeleevian classification for "nuts and bolts" is proposed by Mark Volkmann in The Science Teacher (January 1996).

The third activity is more open-ended. Students are introduced to laboratory techniques and a specific format for recording observations. They mix chemicals without any preconceptions of what may occur in each procedure. From standard textbook definitions given by the instructor, they must create a criteria of their own to distinguish a physical change from a chemical change. The criteria must consist of observable evidence. The procedures chosen include some obvious physical or chemical changes, and some which can be interpreted with less certainty, creating another opportunity for students to defend their conclusions in a peer review. I believe this is a reasonable approximation to the discovery process that Mendeleev and his precursors experienced discovering the sixty-some elements that provided enough of a data base to create a useful generalization such as the periodic law. Student lab reports are evaluated not on whether or not a physical or chemical change is correctly identified, but by how successfully they defend their conclusions based on the observations they made in lab. A large group criteria is then created, hopefully, leading to some consensus. Finally, a lab performance assessment is used via laserdisc, in which students observe a new experiment, make observations, write and defend their conclusions.

Although many students have some previous knowledge of chemistry, they are not allowed to use textbooks until after the three activities are completed. The module has been piloted in a standard college prepartory course and in a course modified for at-risk learners. In both classes, the students were grouped heterogeneously by grade level and ability (no tracking).

History of Elements Classification Schemes

1817

According to Van Spronsen, the first observation of a relationship betwwen the atomic weights (equivalent weight) of elements was made by Johann Wolfgang Dobereiner, of the University of Jena. He found three-member groups of analgous element (triads), for which the equivalent weight of the middle element was the arithmetic mean of the weights of the other members of the triad. He concluded that this relationship must reflect some general principle--which he could not identify.

1827

Leopold Gmelin, University of Heidelberg, expands Dobereiner's triads--again in 1843 and 1852. He was the only other well-known chemist to study this relationship before 1850.

1845

Oliver Gibbs, Rumford professor at Harvard, classifies elements on the equivalents, isomorphism (crystalline form), combining relationships, and types of compounds.

1850

Max von Pettenkofer, Universiyt of Munich, revives Prout's hypothesis of primary matter. Prout believed that all elements were whole number multiples of hyddrogen. Hence, elements would not be indivisible, but have a smaller unit of structure. Pettenkofer expanded Dobereiner's triads. He noted that similar elements formed and arithmetic series and the difference between elements in each series was 8 or a multiple of 8.

1851

Jean Baptisite Dumas, Sorbonne, compared families of elemnts with families of organic comounds. He revived Prout's hypothesis and further refined his system to involve complicated arithmetic progresssions.

1852

Peter Kremers added to Dobereiner's triads. He surmised that four was the atomic weight of a basic element. Multiplication by an odd number yielded a metalloid, even-numbered weights related to non-metals.

1853

John Gladstone's analogies fell into three categories--elements with identical weights, those with weights that are multiples of each other, and those in triads.

1854-55

Josiah Cooke, Harvard, based his system on more than atomic weight--he used isomorphism, electronegativity, physical properties, chemical reactions. His system, like the others, failed to establish a continuous system including all the elemtns because ot the underlying idea that elements could be built up from some simpler form.

1857

Ernst Lessen, Wiesbaden, believed that all elements except niobium could fit into triads. The attempt to classify all elements was encouraging, the results difficult to justify.

William Odling constructs a grouping based on analgous properties. He finds a relationship between four of his thirteen groups.

1860

Matthew Lea, Philadelphia, finds new relationships between atomic weights, even considering negative atomic weights. He attempts to show that the sums and differences of atomic weights gave the numbers 44 or 45. He attempts to predict atomic weights for elements not yet discovered.

1862

Van Spronsen considers this to be the birth year of the periodic system--he lists six discoverers, including Mendeleev. In 1862, Alexander de Chancourtois presented a system showing periodicity as a function of atomic weight in a three-dimensional representation. His Vis Tellurique, so named because tellurium was at the center, was a spiral encompassing a cylinder (also known as the telluric screw).

1865

John Newlands constructs a system of classification based on octaves. His use of atomic weights did not reflect the precision available. His work was ridiculed as having no more basis than if he had chosen an alphabetical listing as a classification.

Odling revises his system to contain 57 elements (Newlands had only used 24), and arranges them in order of increasing atomic weight. Definite groups and subgroups aand gaps in the series (which may have been predictions of undiscovered elements) were the main features of this system. However, he could not explain the relationships his table showed, assuming it would have to include valence.

1867

Gustavus Hinrichs, Iowa State, stated that the properties of of chemical elements are functions of thier weights. He proposed a spiral chart and also had vacant spaces.

1868

As early as 1864, Julius Lothar Meyer, University of Tubingen, presented a system based on valence, but he could for the table could not.

Bibliography

• Mendeleev, Dmitri, An Attempt Towards A Chemical Conception of the Ether, Trans. Kamensky, Longmans, Green , and Co., London 1904.
• Mendeleev, Dmitri, Principles of Chemistry, 6th ed. American Dome Library Co., 1904.

• Ihde, Aaron, The Development of Modern Chemistry, Dover Publications, New York, 1984.
• Jaffe, Bernard, Crucibles: The Story of Chemistry, 4th ed., Dover Publications, New York, 1976.
• Kauffman, George, "American Forerunners of the Periodic Law," Journal of Chemical Education 46(1969).
• Kedrov, B. M., Dictionary of Scientific Biography, New York: Scribner's Sons,1970-
• Leicester, Henry , The Historical Background of Chemistry, Dover Publications, New York, 1971.
• Mazurs, Edward G., Types of Graphic Representation of the Periodic System of Chemical Elements, by author, 1957.
• O'Connor, Davis, Haenisch, MacNab, McClellan, Chemistry: Experiments and Principles, Raytheon Education Company (Heath Division), 1968.
• Pauling, Linus, General Chemistry, Dover Publications, New York,1988.
• Rawson, Don, "The Process of Discovery: Mendeleev and the Periodic Law," Annals of Science, 31 (1975).
• Seshadri, (ed.), Mendeleev's Periodic Classification of Elements, Hindustan Publishing Company, 1973.
• Van Spronsen, J. W., The Periodic System of Chemical Elements, Elsevier, 1969.
• Van Spronsen, J. W. "The Priority Conflict Between Mendeleev and Meyer," Journal of Chemical Education 46(1969).
• Vucinich, Alexander, "Mendeleev's Views on Science and Society," Isis, 42(1967).

Representations of the Element Classification Schemes

• Allchin, Douglas, "The Periodic Table?: On Diagrams in Science," SHiPS News 4(#3): 5-8.
• Mazurs, Edward G., Types of Graphic Representation of the Periodic System of Chemical Elements, by author, 1957.

Activity 1: Elements and Conclusions

• Boss/Reporter -- speaks in large group
• Intimidator -- watches clock, keeps group on task
• Scribbler -- creates poster
• Go-fer -- gets paper, markers, tape, returns tray of elements

Elements: samples in open culture plates, with the exception of nitrogen

• sulfur (lump),
• carbon (graphite rod and piece of charcoal),
• nickel (shot),
• bismuth (crystalline form),
• lead (shiny foil and dull strip),
• silicon (lump),
• copper (strip),
• iron (strip)
• nitrogen (flask full of air, stoppered)

• luster
• magnetism
• conductivity
• color
• odor
• particle size

Teaching strategy

• Demonstrate proper use of magnet and conductivity tester.
• Solicit examples of observations and conclusions from students.
• Assign task: each group is to list conclusions about the elements in their tray for the property they observe.
• When poster is complete, use magnet and/or conductivity tester if they were not assigned as your property.
• Posters are taped to walls--bosses read and explain their group's result.
• Assign task: each student is to write three conclusions which combine information from two properties.-- Intimidator will initial notebooks. Scribbler makes a list of best conclusions from group--turn in to instructor.
• Instructor uses list of conclusions for large group discussion on these topics:
• Are the conclusions verified by the data? How can we tell which conclusion might be the most useful?
• Following discussion, use "The Fable of the Lost Child" (below) to suggest that a conclusion which addresses the largest sample of data may be the most useful. (Also great fun-- segment from Monty Python's Holy Grail, in which Arthur helps a village to decide if a person is a witch).

The Fable of the Lost Child

[This story is paraphrased from the CHEMStudy text, Chemistry: Experiments and Principles.]

Lessons from the story can be organized using the following lists on the board or overhead:

Things That Burn

• flagpoles
• tree limbs
• broom handles
• pencils
• chair legs

• paperweights
• rocks
• marbles

- - - - - - - -
Cylindrical

• pipe
• pop bottles
• car axles

• newspapers

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© The Bakken Updated: April 6, 2007