Matter and Interactions Module
The main purpose of this module is to introduce students to theories and models that can help explain some of the properties of materials, changes in those properties, and interactions between materials. The 'small particle theory' is used in the Physical Changes Unit to account for the properties of gases, liquids, and solids, and changes in state. In each of these physical changes the identities of the materials as well as their mass remains the same. In the Chemical Reactions Unit, students consider situations where the identities of the materials change. They learn how to classify materials according to macroscopic properties, and learn that mass is conserved even during chemical reactions. Students then learn about the small particle theory for chemical reactions, and how elements and compounds are composed of small particles—atoms, molecules, and formula units. They can then 'explain' why mass is conserved in chemical reactions (or physical changes) in terms of these small particles. Students then explore how materials are classified and organized according to their physical and chemical properties (Periodic Table), and how the organization can be explained in terms of atoms and ions and the behavior of valence electrons. Finally, they use a simple model to describe ionic and covalent bonds and explain (in simple cases) the chemical composition of molecules and formula units.
Unit PC: Physical Changes
The purpose of this unit is to introduce students to the small particle theory of gases, liquids, and solids. They observe movies of macroscopic phenomena and computer simulations of those phenomena, and then try to explain the phenomena in terms of the small particle theory. The focus is on physical changes only, not chemical reactions. Therefore, the internal structure of 'particles' (atoms and molecules) is not relevant. Students first consider gases and investigate changes in the macroscopic quantities of pressure, volume, temperature, and mass. This leads them to a statement of the 'Gas Properties Relationship' (a form of the Ideal Gas Law). They are then introduced to the small particle theory of gases, and how to 'explain' macroscopic changes in gases in terms of small particles. They learn that temperature is related to the average kinetic energy of particles and that the 'Gas Properties Relationship' has a small particle accounting, the 'SPT Gas Properties Relationship.' Then they consider liquids, solids, and changes of state, first exploring macroscopic relationships and then explaining them in terms of small particle theory.
Unit CR: Chemical Reactions
In Unit PC, students used the small particle model to explain changes to materials (gases, liquids or solids) that do not involve changes to the physical identities of the materials. In this unit, they explore what happens when materials interact in a way such that their chemical identities change. These interactions are called chemical reactions.
Students learn about the evidence supporting the claim that a chemical reaction has occurred. Then they learn to classify materials as elements, compounds, and homogenous and heterogeneous mixtures according to macroscopic criteria. Next they gather evidence to conclude that mass is conserved during chemical reactions. Then they learn about the small particle theory of chemical reactions, and that elements and compounds are composed of small particles—atoms, molecules, and formula units. They become familiar with both pictorial and chemical equation representations of reactions, which 'explain' conservation of mass during reactions in terms of small particles, and consider energy transfer in both exothermic and endothermic reactions.
Students learn about how elements can be classified and organized, and develop a general understanding of the organization of the Periodic Table. Then they learn how the macroscopic organization of the Periodic Table can be simply 'explained' in terms of atoms, ions, and the behavior of valence electrons. They use the Dot Diagram Model to describe both ionic and covalent bonding, which provides students with insight into why molecules or formula units are comprised of very specific numbers of different atoms. Finally, they use what they have learned to evaluate explanations of chemical and physical phenomena.
