To explore the molecular structure of matter and how it can affect the physical characteristics of a specific material.
By the time they study high-school chemistry, students should grasp the idea that a wide variety of phenomena can be explained by alternative arrangements of vast numbers of invisible, tiny, moving parts. In secondary school, the general architecture of the atom and the roles played by the main constituents of the atom in determining the properties of materials comes into play. Students should learn that though materials differ greatly in shape, density, flexibility, texture, toughness, color, and many other ways, everything is really made up of a relatively few kinds of basic material combined in various ways. (Science for All Americans, p. 46.)
Begin the lesson by saying to students, "Carbon is a very special element because it plays an important role in the chemistry of life. You can find carbon everywhere, from the foods that you eat to the gasoline in your car's fuel tank to the fabrics in the clothes that you wear. Carbon is even used to make bicycle frames."
Then refer students to the Calfee Designs Webpage and ask them to read the Our History. Discuss how carbon is used to make the bike frames and why.
On The Mineral Gallery, have students work in pairs to look up the minerals diamond and graphite. Ask them to list the properties of each mineral and to compare how they differ and how they are alike. Students should notice, for example, that both are composed of carbon. They may also list other properties; for example, graphite is soft, diamond is hard, and so on.
When students have finished their lists, say, "When we looked up diamond and graphite on The Mineral Gallery website, we found that both substances were made up of only carbon atoms. Yet the two materials couldn't be more different. While graphite is soft and slippery, diamond is the hardest substance known to us. If both are made only of carbon, what gives them different properties?"
Have students read Is Carbon Hard Or Soft? Have each student perform the activity in which a four-sided pyramid and a cube are built out of straws. Each student should determine which shape is strongest by devising various ways to test for the strength of each shape and write his/her explanations in his/her science notebook.
Have students explain why the pyramid is like diamond and the cube is like graphite by referring to the diagrams of the structures of the two substances. Also refer them to illustrations of diamonds and graphite on the MathMol page. Ask students to determine if these illustrations help to explain why graphite is soft and diamond is hard.
Next, have students view the Java applets on graphite and diamond found on the Reciprocal Net Common Molecules website. Ask students to describe how the animations demonstrate that diamond is hard and graphite is soft.
Once students have discovered that the differences in the two materials lie in the way the carbon atoms form bonds with each other, have them view and compare the fullerene or buckeyball molecules in the MathMol database and the java animation from Reciprocal Net Common Molecules. Again, discuss how the molecular structure, as demonstrated by the diagram and the java applet, help to explain the properties of the materials.
Finally, students should look up lonsdaleite in the Mineralogy Database. This is a rare, hexagonal polymorph of diamond, believed to be formed when meteoric graphite falls to earth. When this happens, heat and stress transform the graphite into diamond, but it retains graphite's hexagonal crystal lattice. A polymorph is a mineral with the chemical equivalence (i.e., containing the same amount of the same elements) of another mineral but with a different arrangement of atoms. Compare the information on the lonsdaleite chart with that on the diamond chart.
- Where is the principal difference? (Have students click on the link for the crystal system of each mineral.)
- Are they the same?
- What are the differences?
- Lonsdaleite is thought to be extraterrestrial in origin. What does this tell you about carbon?
Have students draw a flow chart in which they explain what happens to the graphite molecule when lonsdaleite is formed.
Explain to students that the fullerene was named after Buckminster Fuller, who designed Geodesic Domes.
Assess student understanding by asking the following questions:
- Why is this name appropriate?
- If you had to rename the diamond and graphite molecules based on how their structure looks, what would you name them? Explain your answers.
MathMol (Mathematics and Molecules) is designed to serve as an introductory starting point for those interested in the field of molecular modeling. The Water and Ice module on the site is also a good source for exploring the properties of a substance based on its molecular structure. MathMol also includes a hypermedia textbook for students in grades 6-12 and links to public domain software that can be used for molecular modeling.
The book Carbon, by Sparrow Giles, provides additional information related to this topic.
For an additional Physical Setting lesson for grades 9-12, go to the Science NetLinks lesson entitled Earth Movers.