3.091 | Fall 2018 | Undergraduate

Introduction to Solid-State Chemistry

Instructor Insights

Interview: “Why this Matters” Moments

In this section, Prof. Jeffrey Grossman discusses the importance of putting concepts from the classroom into real-world context_._

"I hear from students, all the time, that as soon as I put the ‘Why This Matters’ moment in front of them, they sit at the edge of their seats."
— Prof. Jeffrey Grossman

Just because I’m teaching a lecture on the periodic table, or on Lewis structures, or on X-ray generation, that doesn’t mean I can’t connect the topic the students are learning to some bigger-picture question or something that’s more broadly accessible. I want to make sure that we have that connection in every single lecture. So I always take what I call a “Why This Matters” moment (it’s really my “Why This Matters” five moments, or ten!), and I connect what we’ve learned in that lecture to some pressing global challenge or some technology that the students all know or can relate to.

The question “How can a single chemical reaction feed billions?” is a perfect example. When I’m teaching about balancing chemical reactions, and about yield and limiting reagents (the chemicals that will run out first in a given reaction), I use the reaction of fixing nitrogen as the example. Now fixing nitrogen has enabled us to overcome one of the biggest problems in agriculture, which was to have enough fertilizer. Plants really need nitrogen, and though 78% of the air is nitrogen, that form of nitrogen is useless to plants. They can’t use the N2 molecule, nitrogen gas, but they can use the NH3 molecule, which is ammonia. The question is, how do you make nitrogen gas into ammonia? And that’s called fixing. I tell my students about the Haber-Bosch process, which enabled that to happen at a global scale, and then I ask some fun questions that are related to what we just learned, like “Okay, what is the limiting reagent? If we fix nitrogen for the next thousand years, are we going to run out of N2 in the air?”

I like to take these questions and examine them at a larger scale. And what you realize is that no, we won’t run out of nitrogen in the air for a long, long time. But it also helps you to connect something that we just learned to a really important problem, which is how to have enough fertilizer, enough ammonia, to feed billions of people. When the Haber-Bosch process was invented, it resulted in an uptick of population growth on planet Earth, because now you could make enough NH3 to feed many, many more people. That’s a great example of taking a simple chemical concept and giving it a bigger context.

For another example, when we cover the discovery of the electron, which is so important for the foundations of chemistry, I talk about how electrons were discovered in an experiment with a cathode ray tube, but I also talk about how the electron made a blip on the screen in that experiment, and that’s how we knew a lot about it. We knew that the electron was there, we knew that the electron could be detected.

Why This Matters Excerpt: The Age of Atomic Design

And so that’s when we get into the structure of the atom. But what about that blip itself? What’s that about? And then we talk about the invention of television and screens, and using electrons to make images. So the “Why This Matters” moment involves asking, “How did that happen, and what was the chemistry that was needed to have the ability to paint with electrons, and how is that useful to you even today?”

This is something we can do in any class we teach, whether it’s advanced algebra or Python programming or civil engineering. Every time we teach, we can take what we’re teaching and try to give it some sort of context, and give the students an example of how what they’ve just learned connects to something else. I hear from students, all the time, that as soon as I put the “Why This Matters” moment in front of them, they sit at the edge of their seats. They get really interested. It helps keep them engaged in what we’re learning. The “Why This Matters” moment is also really important for me, because it makes me excited and every year it makes me come up with new ideas for how to relate the material to some bigger-picture aspect of my students’ lives.

Course Info

As Taught In
Fall 2018
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Instructor Insights