One of my high-school age learners is working on chemistry with me this year. We went through the standard high school curriculum up through the point of stoichiometry. After that point, the curriculum branches off into topics like oxidation-reduction reactions, acids and bases, and so forth. We found that picking up the topics in order was starting to be tiresome. And so, as we are wonderfully spoiled with a non-traditional learning environment where we expect learning to be driven by curiosity and exploration, we started to wander in search of a better method of study.
What we hit upon was browsing around various resources, finding interesting topics and questions and doing a kind of guided cooperative research discussion. I provide some background knowledge, we both contribute curiosity and questions, and we are both enjoying it and learning a lot.
Lately we’ve been investigating some basic organic chemistry, looking at the structure of alkanes (hydrocarbons with only single bonds connecting the carbons). The textbook gave us a table of the melting points and boiling points of the different alkanes and we noticed something surprising. The boiling points increase in a smooth logarithmic curve, but the pattern in the melting points is much more erratic and is not even always increasing as the number of carbons increases. Here’s a graph he made. Orange dots are boiling points, green dots are melting points. The x-coordinates are proportional to the number of carbons in each alkane.
What’s up with those first three – methane, ethane, and propane? And then look how they’re paired off for a while – butane close to pentane, hexane close to heptane, and octane super close to nonane. So strange! We’re curious and we’re investigating.
We found this excellent web application, MolView, that allows easy 3D modeling of molecules. We think the different non-structural isomers of the various alkanes may explain the strange pattern in their melting points.
Anyone know the answer to our mystery?