“How does structure influence reactivity?” is a question of connection between chemical structure and behavior. The specific ways in which the submicroscopic particles of matter interact with each other and are transformed into different chemical species depend on their atomic composition and molecular structure. The types of atoms present in a molecule and their relative arrangement in space affect the distribution of the electrons that can participate in bonding processes with other particles. Understanding how molecular structure affects electron distribution, and how this in turn determines how different particles interact and react with each other is critical to design the synthesis of desired materials and to control chemical processes.
These formative assessments were developed by past ACCT cohort members.
The Dietary Calories formative assessment asks students to do an energy survey to probe how students think about energy in their diets. The formative assessment task reveals students’ thinking about structure-property relationships and chemical mechanism by getting students to look at food labels to try to figure out where in the ingredients the calories come from. Students are asked to share and explain their thinking about the energy content in food and justify their explanations based on models of structural formulas of some ingredients. Students reveal even more thinking about structure-property relationships when asked to explain the relationships between the energy content in food and the energy changes witnessed in combustion reactions.
This formative assessment was designed to target students’ thinking around the structure-property relationships in an accessible, real-world context. This is done through targeting noncovalent interactions. The understanding of this topic is critical for students’ reasoning about observable properties of matter.
In “How strong an acid is vinegar?” the students explore the nonlinear relationship between the concentration of a weak acid and the pH of the solution. This formative assessment targets the question “how does structure influence reactivity?” Students need to understand the behavior of strong and weak acids to comprehend phenomena like buffering capacity.
This formative assessment looks at two household chemicals (table salt and sugar) and compares their properties while looking at how they dissolve in water. The “Salt vs. Sugar” formative assessment explores students’ thinking about the question “How does structure influence reactivity?” The main idea that is being targeted is for students to think about what is happening at the molecular level during the solution process. This activity is important for students because it helps create a context for what some of the vocabulary and concepts mean by providing tangible examples of these concepts (such as the concept of saturation).