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Overview
The ChemSense curricular framework highlights collaborative investigations, representational competence, and chemical change. ChemSense curricular modules are co-developed by teams of researchers, developers, and teachers. Each module contains learning objectives, hands-on experiments, and integrated chemistry tools. See examples of student and teacher work and sample curriculum activities.

Key Chemical Themes: Chemical Change
Our curriculum is designed around a set of five key time-dependent dimensions that we have identified as associated with the particulate nature of matter and chemical reactions: change in (a) connectivity, (b) molecular geometry, (c) aggregation, (d) state, and (e) concentration. Taken together, these dimensions begin to portray the molecular world imagined by chemists to account for observable phenomena. All involve changes in molecular and supramolecular structure that correspond to critical aspects of chemical reactivity. In addition, these time-dependent dimensions cut across more traditional chemical topics, such as acid-base reaction, electrochemistry, solubility, kinetics, and thermodynamics. Sample curriculum activities are available.

Connectivity. The connectivity of atoms to make molecule structures sits at the core of contemporary chemistry. Chemical identity is expressed in terms of the molecular structure. Patterns of observations on many thousands of sophisticated chemical examples have led to one of the most important advances in chemistry: the structure-reactivity relationship. Chemical reactions, that is, the transformation of one set of compounds to another, are changes in chemical identity and are expressed in terms of connectivity changes. These patterns of connectivity are often associated with certain perceptual qualities of a compound.

Molecular Geometry/Shape. Molecular structure involves more than connectivity; molecules also have shape. And chemical changes involve more than changes in connectivity. A complete understanding of chemical reactivity also involves understanding the changes in spatial relationships that accompany chemical change––changes in shape. Sometimes, changes in shape influence greatly the understanding of the chemical process. Changes in biochemical systems are a good example. Other times, the changes take place and there is no particular impact.

State. The state of a molecule within a set of molecules is the full inventory of energy relationships that exist. Heat and light are the two most common sources of energy that influence changes in state. Phase change is an example, where the relationship between molecules depends on the temperature of the environment. When molecules absorb or emit light, this process also involves a change in state.

Aggregation. The aggregation of molecules is influenced by a variety of intermolecular and intramolecular interactions. Why do some salts dissolve in water and others do not? Why do some things mix while others do not? Forces of aggregation also strongly influence our understanding of biochemistry because, in general, multiple molecular units must spontaneously assemble in order for specific chemical reactions to be catalyzed. An understanding of drug design, including mode of action, relies heavily on understanding the relationships that exist in molecular clusters.

Concentration. When materials combine to undergo chemical reactions, large collections of molecules mix, colliding with one another. All measures of concentration express "the number of molecules per unit volume." Changes in concentration affect the number of collisions that can take place between the different substances. The higher the concentration, the more molecules of one substance will be able to collide with those of another. The greater the number of collisions, the greater the likelihood that a productive collision takes place. The effect of concentration on reactions is an important topic in understanding the particulate nature of matter.
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