"A chemist", Primo Levi wrote in an essay on carbon, "only has to leaf through a treatise, and memories rise up in bunches." When my wife became curious about the whereabouts of former fellow chemistry graduate students, I suddenly remembered one of my peers nicknamed "Padma". In the lab where I was working on an undergraduate project, he was completing his doctorate on the synthesis of spiroaxane sesquiterpenoids. Spiroaxanes are natural products that are found mostly in various marine organisms and mushrooms. The general class of compounds known as sesquiterpenoids contain 15 carbon atoms; they're  made up of 3 basic units of isoprene and can serve as protective agents or chemical messengers.

For life to begin, a combination of inorganic and organic substances need to evolve biochemistry. When 20th century scientists accepted and elaborated on J.B.S Haldane's primordial soup hypothesis, their guesses and suggestive experiments centered mostly around the mature field of organic chemistry. But biochemistry as a science was still in its infancy. Their hunches were like those of aliens trying to account for our transition from hunter gatherer-groups to civilization without understanding the roles of agriculture, division of labor and writing.

By definition, elements, whose atomic nuclei have the same number of protons, and compounds, which have two or more elements bonded together, are both pure substances. Not to confuse the "pure substance" term with chemical "purity" in the analytical sense, what matters more is that pure substances can be anywhere on the spectrum in terms of how they impact humans and the rest of nature. When evaluating chemical elements and compounds from this point of view, the following classification may prove useful.

1. Not Quite Perfect Superheroes: Essential Life-Giving Substances 
 

Two summers ago, I was eating fruit in the sun when I noticed that a wasp had found a fragment of my pear on the deck. The piece was only about a centimeter cubed in volume but heavy enough to prevent the wasp’s takeoff. Soon after its unsuccessful straight-up takeoff attempts, the wasp dragged the little pear morsel across the deck for about two and a half meters until it reached the edge. Once off the deck, the wasp was able to fly away with its meal.

School years are cyclical, so over the years teachers could end up feeling like Sisyphus, forever condemned to rolling a boulder up a hill, watching it go down, only to have to push it up again. Of course, things don't have to be that way. Once in a while, one can get creative, or at least whimsical and spice things up.  And what better time for some carefully orchestrated, chemistry antics than on the last day of school?

This year's finale might turn out to be the most memorable, so we'll save that story for last.

Numerical results are not gospel. After crunching them again, even if they turn out to be valid, time is not lost. Investigating will often teach one something. So to learn a little more, I wondered how the EPA arrived at the figure of   8.92*10^-3 metric tons CO₂/gallon of gasoline.

First, since I'm a middle-aged Canadian half-raised on imperial gallons and half on liters, I'll begin with a more trivial matter---a conversion: