The Space Below Aluminum

Stick with me, I promise this will all make sense in a little bit.

This story starts with diatomic elements like oxygen and hydrogen — not quite the opening you were expecting, I know. Oxygen and hydrogen are diatomic (i.e., they consist of two individual atoms bound together) naturally in their elemental state. They do not exist as single atoms naturally like helium or neon. This seems like a relatively inconsequential fact, but historically, this gave early chemists the biggest pain in the ass.

When John Dalton first proposed the existence of atoms and atomic weights in 1803, chemists were all about the “hydrogen balloon” experiment — the combustion of hydrogen with oxygen creates an impressive fireball and water vapor. They were more scientific in their approach than simply exploding a balloon, and ultimately determined that 2 volumes of hydrogen reacted with 1 volume of oxygen and yielded 2 volumes of water vapor. This result ONLY made sense if hydrogen and oxygen were diatomic — props to Amadeo Avogadro who first proposed this concept in 1811.

Here’s the rub (and ultimately why his hypothesis failed to catch on right away): his initial explanation for how diatomic elements fit into the interpretation of the hydrogen combustion experiment seemed to suggest that atoms would split (he didn’t — Avogadro was extraordinarily careful to use very specific terminology to avoid this very problem, but that’s neither here nor there). In the universe where Dalton is god, anything contrary to the indivisibility of atoms is heresy, so Dalton put the kibosh on Avogadro’s hypothesis immediately. This had the domino effect of resulting in multiple interpretations of the experiment, which then caused the adoption of multiple sets of atomic weights. Subsequently, an entire generation of chemists had to endure the confusion that ensued from multiple sets of relative atomic weights.

It wasn’t until 1860 when Stanislao Cannizzaro revived Avogadro’s hypothesis at the Karlsruhe Congress that the idea of diatomic elements finally saw widespread acceptance. The concept of the atom then moved from metaphysical to practical, and the first benefit was the standardization of atomic weights. Up to this point, chemists were working multiple sets of relative atomic weights, which were the byproduct of multiple interpretations of the aforementioned hydrogen balloon experiments. Now, all atomic weights were standardized, which eliminated a lot of confusion and legitimized chemistry as a science even…