piqued my interest, but ultimately was a pretty dry read.
Mendeleev finished his periodic table in the late 1800s, and in the early 1900s, Henry Moseley discovered Atomic Numbers, not Atomic Weights were the main driver of the periodicity of the elements. At that point, there were seven holes-- seven spots where there should have been an element smaller than Uranium. The race was on.
The discovery stories were pretty pedestrian. Researchers from different countries argued very politely that their discoveries were real. I would have liked to know more about the discoverers. Some of them sounded pretty interesting. Moseley was killed in WWI. One died of radiation poisoning. One was a pilot in the french resistance, but these were just mentioned, while the author spent pages talking about X-Ray chromatography and priority.
Notably, 3 of the 7 elements were discovered by women. These women seemed really interesting.
Also, I'd sure love to understand why some nuclei are stable and some aren't. Why can't Technetium create a stable nucleus while everything around it is boring?
Anyway, it's a fascinating subject but a boring read. A better read is in the XKCD What If book -- not online, but somebody's excerpted it here: