Like most concepts in chemistry, intermolecular forces takes a bit of imagination and critical thinking to fully comprehend and apply when explaining a variety of situations. Though demonstrating the presence of these forces in a simple and explicit manner can easily be done, I wanted to change how I introduced IMFs a bit this year by focusing on a more data-to-concepts approach.
In an effort to align an old VSEPR lesson to NGSS, I told my students that we were going to look at the data available from the real molecules on the pHET simulation we were using and specifically look for patterns. Finding patterns is a cross-cutting concept; one of the three dimensions of NGSS.
When describing abstract concepts like chemical bonding, it always seems to feel far too easy for both teachers and students to resort to the “wants” and “needs” of atoms. After all, we understand what it means to want, need, or like something, so it often feels appropriate (and easier) to use a relatable metaphor or subtly anthropomorphize these atoms to accommodate our students’ current reasoning abilities. While predicting the types of bonds that will form and the general idea behind how atoms bond can be answered correctly using such relatable phrases or ideas, the elephant in the room still in remains—do our students really understand why these atoms bond?
In this blog post, I'll discuss how I've expanded my use of model kits within my chemistry class to help explore a variety of topics with my students.
I have always struggled teaching the concept of bonding. What is a chemical bond? Is it just covalent or ionic? What about hydrogen bonds? Are those real bonds or just attractive forces pretending to be bonds? If they are not official bonds, what do we call them? How about intermolecular forces? How are those different from salt crystals that attract to other salt crystals but are called ionic bonds? How about "electronegativity"? If there is a metal nonmetal compound but it is just shy of the "cut off" for the difference between polar covalent and ionic, what type of bond is it? Essentially, as I got confused over the years, this translated into confused students and rushing on to get to the next unit in an attempt to cut my losses.
We just finished an introduction into ionic and covalent bonding. Somehow I wanted to try to figure out what they did or did not take away from the experience but because we just finished semester exams, I did not want to do another test or quiz. Instead, I tried a "card sort".
In this Activity, students compare polystrene and cornstarch packing materials ("peanuts"). Both are made of polymers, but because of their composition, they behave very differently in various solvents. Students extrapolate how these differences in behavior relate to environmental effects, such as filling landfills with non-biodegradable materials.
In this Activity, students build models of polarized water molecules using K’nex toy components and adhesive Velcro. Students investigate hydrogen bonding by shaking the models in various ways. They observe the resulting interactions and relate their observations to physical states of water and the difference between strong bonds and weak attractions.
In this Activity, students first prepare a gel using the superabsorbent polymer sodium polyacrylate (found in certain diapers) and water. The gel is split into piles and samples of different compounds are sprinkled on the piles. Students determine that ionic compounds break down the gel, while covalent compounds have no effect on the gel.
In this Activity, students use their deductive reasoning skills as they identify formulas of unknown elements and compounds modeled by paperclips. Each color of paperclip represents a different element, with linkages between different paperclips in appropriate ratios representing 20 unknowns.