Chemistry of Everyday Things

Rationale

In High School chemistry, we spend much time on the structure of the atom, the arrangement of electrons around the nucleus and the position of the atom on the periodic table. We do indeed look at bonding and maybe get into the shape of a molecule and how that might influence the properties of a substance. I would argue that a typical beginning high school chemistry student will have the impression that chemistry is all about individual atoms and less about the molecules themselves and the arrangement of said molecules. Phillip Ball in the opening chapter of "Stories of the Invisible: A guided Tour of Molecules" states that "molecules are the smallest units of meaning in chemistry." ¹ He makes the analogy that atoms are like letters and that molecules are like words, where longer words are more subtle and the order of the letters (atoms) are important. He suggests that we can invent new molecules (words) that can replace whole sentences and tell new stories. ¹ A molecule is the fundamental piece of matter. Certainly by changing some atoms in large molecules we can subtly change the properties of that substance, and so, knowledge of the atomic structure is important but more secondary.

Roald Hoffmann suggests that chemistry is the science of molecules and their transformations. Some molecules are just waiting to be discovered, whereas many more molecules are waiting to be made in the laboratory. Nearly ten million new compounds have been made by man. ² They are not found naturally. Primo Levi in "The Monkey Wrench" likens a chemist to an engineer who just builds and dismantles very tiny constructions. ³ Yaron, Leinhardt and Karabinos in their paper identifying critical resources for thinking in Chemistry, suggest that chemists analyze matter to determine its composition, they synthesize and design new combinations for particular purposes and that they explain actions and reactions of molecules at the atomic and macroscopic level. This movement from levels of scale makes chemistry a difficult topic to master. Their analysis of recent chemistry findings and Nobel prizes showed an emphasis on synthesizing or design activities, analytic activities and explanation activities. ⁴ The activity of designing and synthesizing refers to the construction of new materials for desired properties. We can now make synthetic skin, blood and bone. We can make an information highway from glass. We can make materials that repair themselves, that swell and flex like muscles, that repel any ink or paint, that capture the energy of the sun. ¹ We are now in a position to design a material for a specific application.

This unit is designed for students to make observations at the macro-level and then link molecular structure at the nano-level to the properties. Most of Chemistry 1 involves very small molecules and so the basic properties of these individual molecules will be used as building units for bigger molecules. It is not unreasonable to expect Chemistry 1 students to link small molecules with weak intermolecular forces to gaseous behavior, long stringy molecules to more fluid behavior and small polar molecules to strong crystalline structures. Some consideration will be given to assembly and the relationship to both overall structure and the nature of sub units. Analogies will be made with the macro-level. For example the strong fibers of the body such as skin and nails are made from keratin which consists of proteins twisted together like a piece of twine or strong rope. Looking at various ropes/string and what makes them strong will help students understand the assembly process at the molecular level. If students understand that bonds are strong attraction between atoms and that intermolecular forces are also attractive forces that are just weaker, then they should be able to understand at a simplified level what is necessary to bring about some of the desired properties.

Again Roald Hoffmann suggests that the synthesis of molecules puts chemistry very close to the arts and represents a highly creative activity. ² Since I teach gifted students, I want to show them the opportunities to be creative in the scientific world. They always seem to relish these opportunities to design something new and should be encouraged to develop this type of thinking. Whenever a teacher is able to show how what has been learned can be applied to the 'real world', then the learning seems to be both deeper and richer. So with this unit, I would like students to think of a material that they think would be useful or even fanciful, and then determine the required properties of this material at the macro-level and then translate these properties to molecular structural requirements. As mentioned above this may only entail designing the necessary sub-units without actually designing an assembly process.

The design of the material and sub units would be the culminating activity for the unit.

The first activity of the year for my Chemistry 1 class is an examination of several substances that are similar and the students are asked to distinguish between them. They compare three metals- one is malleable, one has a very low density and one is stiff. They compare three liquids- one has an odor, one is more viscous. Three plastics are compared and again they vary in ability to be stretched, flexibility and transparency. Finally the interaction of water with three white powders is studied. One dissolves in water, one repels water and one absorbs the water. So I start the year with the idea that chemistry is about why different substances have different properties. An early unit in my Chemistry 1 course is an exploration of the properties of solids, liquids and gases. The students then relate these properties to the arrangement of the particles of matter. At this point, we refer to particles and really do not distinguish between atoms or molecules but rather establish the particulate nature of matter. At this early stage, students are able to recognize that if water is a liquid at room temperature and that carbon dioxide is a gas, then there must be a stronger attraction between the water particles than the carbon dioxide particles. The subsequent units that follow include atomic structure, basic bonding, nomenclature, moles, stoichiometry, etc. The fourth quarter begins with a second unit on bonding when Lewis structures, VSEPR and intermolecular forces are discussed. From there, we study the solution process and look at the impact polarity has on solubility. I would see this unit coming after the solubility unit, almost at the end of the year and tying together the opening units. Now, the students have the tools to see the connections.

The unit would begin by looking at plastics and their varying properties and relating these differences to molecular structure. Since nanotechnology is very hot now and some exciting work is being done at a local college, the University of Pittsburgh, nanotubes and some other nanomolecules will be studied. These series of examples will give students an opportunity to see the connection between the properties and molecular structure so that they can then give free rein to their imaginations.

While we will not be focusing on actual production methods for these molecules, I would like to discuss the responsibility of making products that are not detrimental to the environment. While plastics are materials that we use everyday in large quantities, they have filled our landfills and even broken down to give toxic substances. I would like

students to realize, that rather than looking at recycling as a tool at the end of product use, material design should look at eliminating waste and having end products be biodegradable. The principles of green chemistry will also be part of the unit.