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.Level: Grades 10-12
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).
William Odling constructs a grouping based on analgous properties. He finds a relationship between four of his thirteen groups.
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.
Elements: samples in open culture plates, with the exception of nitrogen
[This story is paraphrased from the CHEMStudy text, Chemistry: Experiments and Principles.]
Things That Burn
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