# In Chemistry, students draw upon data, reasoning, and prior knowledge to figure out core ideas.

In the second block of Chemistry, our focus is on how electrons determine chemical properties. This block we won't do many labs, though we'll make up for that during build week, when we introduce equilibrium with four long labs. In most classes I provide a list of problems and the students work on them either alone or in groups, asking me questions as they come up. I've chosen and ordered the problems to try to guide the students through a new topic, so they can figure out ideas for themselves based on data, reasoning, and prior knowledge. After the students have worked through the ideas on their own and have some conceptual idea of what's happening, then I give a brief, informal introductory lecture on the topic to solidify their understanding and make sure they have the standard terminology down.

We started with a week on stoichiometry and basic chemical calculations. In a normal class, I would have to teach each type of problem as a separate procedure, but at Proof School, with a few definitions the students got to work and successfully completed most of them. As a former Proof School math teacher put it, the problems are mathematically simple, so even if it doesn't feel easy, the students can figure them out. Some of the composition problems (based on data used by Dalton in developing the Atomic Theory) led us into a discussion of oxidation states of main group metals. On a quiz focused on nomenclature, students dug deeper into oxidation state patterns in the periodic table. The "mod 8" pattern became clear, and some noticed an additional pattern that foreshadowed the subshells of quantum mechanics.

We then started our studies of quantum mechanics. Students observed continuous and discrete spectra in lamps, and the emission spectrum of atomic hydrogen. They studied the emission lines of hydrogen to look for the patterns described by Balmer and Rydberg, then tried to recreate Bohr's work describing the hydrogen atom using a "solar system" model. About half the class has already seen calculus, so we did a brief discussion of Schrodinger's Equation and then students looked at the hydrogen atom wavefunctions using Wolfram Alpha. Students developed the idea of effective nuclear charge by looking at data and thinking about familiar physics. Some started to look at the data used to create quantitative electronegativity scales. With this background, they were ready to make the connections between the hydrogen atom wavefunctions, electron configurations, and the periodicity of the periodic table.

In the remaining weeks of the block, we'll look at Lewis structures in some detail, geometry prediction, and introduce molecular orbital theory. We'll also review energy concepts as we discuss bond energies, and review phases as we study intermolecular forces.

*-- Emily Eames*