Making Scents of Molecular Geometry
Making Scents of Molecular Geometry

"We know a lot about what we hear, but we don't know much about how we smell," explained Upper School science teacher Jeffrey Rubel to his Honors Chemistry students.

Students are currently working on a unit about molecular geometry, polarity, and intermolecular forces. One of Mr. Rubel's goals is to make each unit relevent. "Chemistry can often seem very disconnected from a student's lived experience," shared Mr. Rubel. "This lesson on smell was designed to demonstrate how what we have been discussing about molecular geometry can affect how students experience the world through smell."

The class included an introduction to the characteristics of odor molecules, a brief history on the study of smell, and a discussion on why it's so hard to make robots that smell. The lesson concluded with a smell lab assignment.

To start, students learned that the relationship between smell and molecular geometry is "quite nuanced," explained Mr. Rubel. "Yes, there is some correlation between a molecule's shape and its smell, but it's a lot more complicated than that. There's still a lot we don't know."

An overview of smell studies history illustrated how the understanding of smell is still evolving. Mr. Rubel shared the contributions of scientists from the 1940s through the 2010s. "I wanted to show students how our knowledge is still developing. It's important to know that our knowledge grows through the contributions of many people over many generations," shared Mr. Rubel.

Students were especially interested in the challenges of developing robots that can detect smell, discussing the question, "why is that so hard?"

"If you put all of the molecules in the robot, it's hard to get them all together and manipulate them," suggested a student. "We don't even know all of the shapes," replied another.

"Smell is a psychological thing and it takes place in the head," added Mr. Rubel. "We can get a robot to detect the presence of a molecule, but it's much harder to get it to know how the brain registers those molecules as a specific smell."

"Like dogs depend more on smell and we rely more on eyesight," observed a student. "They have more receptors and are lower to the ground. But not everyone can have a dog, so a robot could help a lot of people."

"Yes! Diseases have smells and if we had robots that smell we could maybe catch these things," said Mr. Rubel. "It could be an astronomical development in the medical world. This discussion showed students why what we're studying matters and how it can save lives," said Mr. Rubel.

Students then enthusiastically took part in a hands-on lab, stopping by 16 stations to determine unlabeled scents through their masks.

"This smells like nail polish," remarked a student. "This is kind of strange, is it licorice?" asked another.

"I didn't say this would be easy," said Mr. Rubel. "It can be very hard to smell out of context, isolated in a small glass vial."

"Eww, this is not a good smell at all!" observed a student. "What is carraway? It's a spice," explained another student.

At the completion of the lab, students compared their results with the answer key which also included the molecular structures of each smell. The lab allowed students to compare molecular geometries to a molecule's smell, identifying if smells they mixed up had similar shapes.

"I think this hammered home that the relationship between smell and geometry is really tricky," added Mr. Rubel. "In some cases, students did mix up smells with similar shapes; in other cases, molecules with very different smelled quite similar."

"How do you get the molecules to align?" asked a student.

"Maybe one of you can go and get a Ph.D. and help answer some of these questions," smiled Mr. Rubel. "I'm on it!" added a student.