is Julius Thomsen's birthday. Thomsen was a Dutch chemist who first identified a need for a period on the periodic table with a valence number of zero. His reasoning was based on how some periods had positive valences and others had negative valence, so there must be a period where the transition occurs between positive and negative. He also predicted these elements should have atomic weights of 4, 20, 36, 84, and 132.
His hypothesis would be later be shown to be correct. In 1895, Carl von Linde would discover these elements and call them the noble gases
. Find out more about Thomsen and what else occurred on this day in science history
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