We did another chalk talk today. It was less successful. The task was to compare and contrast ionic and molecular bonds. They had done this for homework, taking notes from their book as they read. I think it was less successful because it was less open-ended;there was more a sense of needing to have a correct answer to put up there.
After the chalk talk, I clarified, we reviewed electronegativity, I gave them examples of polar bonds, we reviewed salts (and how they are always ionic), and we diagrammed a salt (KOH) and a polar molecule (NH3) dissolved in water. The KOH was on their homework.
A hint to remember for next year–Hydroxides are confusing examples of salts, because of their OH bond. When you tell students to memorize OH, NH, OC, and NC as important polar bonds, and then give them a salt with an hydroxide ion, they get confused. It is too many concepts to deal with at once. Save the hydroxide ions for when they are good at polar/ionic classification, and after salts and hydroxide ions have been reviewed.
I made up more practice problems having them diagram the dissolution of ionic and polar compounds.
I just realized today that I forgot to emphasize “like dissolves like.” I consider that fairly central to the concept of dissolution. I will have to figure out a way to bring that in.
