The Moseley Experiment
How we know what we know about the order of the elements on science’s most famous table
I’ve written about Dimi Mendeleev before — he’s probably one of my favorite famous chemists. He’s just so prototypical Russian in how he looks, and I imagine that contrasting with how brilliant he was as a scientist. I don’t even know if “Dimi” was his nickname or not, but to me, it fits. In terms of popular contributions to the science, it’s hard to beat his development of the periodic table — the most famous table in chemistry, if not all of science. He characterized all the elements systematically and recognized patterns, which was not all that unique among similar efforts that were ongoing at the time. Further, his organization of similar elements based on his pattern recognition into a table that was simple and logical was received with little fanfare until he made three bold predictions about some missing elements. All these predictions turned out to be uncannily accurate, and thus, the legend of Mendeleev was born.
The first principle of Dimi’s organization of the table was to order elements by atomic weight. This seemingly simple task was actually not possible until chemists finally agreed on one set of atomic weights. Until 1860, there were two sets, the “O=8” set and the “O=16” set; my discussion on the Avogadro Hypothesis…
