From 2000 to 2007, I worked as an illustrator, art developer, writer, and editor for the University of California at Berkeley on a high school chemistry curriculum development project called Living by Chemistry. LBC, headed by Professor Angelica Stacy of UC Berkeley’s Chemistry Department, began with a grant from the National Science Foundation and is being published by Key Curriculum Press.

Menthol molecule: space-filling model

Menthol molecule: ball-and-stick model

The sequence of images to the left emphasizes the importance of discerning structure despite altered orientation. Both molecular models represent dichloromethane (two chlorine atoms and two hydrogen atoms arranged around a central carbon atom), even though their positions make them look different in the first frame.


Molecules with symmetrical structures tend to have an even distribution of bonding electrons, and are therefore called nonpolar. Nonpolar molecules do not interact with receptor sites inside the nose, so gases like nitrogen, carbon dioxide, and oxygen are odorless.

Molecules with asymmetrical structures tend to have a relative excess of bonding electrons (and therefore a negative partial charge) at one end, and a relative deficit of electrons (and therefore a positive partial charge) at the other end. Such molecules are said to be polar. Polar molecules like hydrogen sulfide and ammonia smell because they interact with scent receptor sites and send nerve signals to the brain.

Building ball-and-stick models from a kit.

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