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Question: Why did we switch from Latin to English in naming the elements in the Periodic Table?
No such switch has occurred. From the late 1700's to the present, English has adopted the Latin names, mostly ending in –ium, for nearly all newly discovered elements: 91 out of 92. The 23 older elements, discovered prior to 1776, often have different names in English than in Latin. Some simply lack the Latin suffix (for example, carbon vs. carbonium), but others, often rooted in the Germanic origins of English, have nothing in common with the universally-used Latin-based symbols that appear in the Periodic Table. Examples include iron (Fe), gold (Au), and lead (Pb).
So why, I wonder, did you think that the naming of elements switched from Latin to English? If anything, the reverse seems to be the case. The few non-Latin names are the oldest not the youngest. As a teacher, however, I have learned that nearly every question contains a germ of truth. And I think that's true of yours. Looking at the last 235 years of element naming, we can see that the root to which –ium has been added to form new names has gradually drifted away from Latin roots referring to minerals (for example, calc-ium, literally 'limestone'-'element'), physical properties (oxy-gen, 'acid-making'), or mythical beings (Titan-ium). In their place have come more familiar-but only rarely English-roots. Now that I have identified the germ of truth underlying your question, I will try to answer the question itself: Why did this shift occur?
The single most important factor appears to be that many new elements occur only rarely and lack any useful properties. Physical theory predicted their existence, and scientists have vied for the honor of being the first to observe them, usually as expected byproducts of nuclear reactions, whether in bomb-testing or in laboratory settings. But these typically radioactive and quick-decaying elements do not occur in substances found in everyday life, nor, in most cases, possess any practical value. So the Latin, and English, names for many of them derive not from the Latin roots referring to attributes of the discovered elements, nor from the proper names of powerful gods, but rather from the personal attributes of the discoverers: their hometown, nationality, favorite physicist, laboratory location. Examples include americium, berkelium, and californium, which were named by scientists in the U.S.A., Berkeley (home of a prominent research university), and California; dubnium, named after the town of Dubna, site of a proton accelerator in Russia; and einsteinium and fermium, honoring famous nuclear physicists: Albert Einstein and Enrico Fermi.
So, although there's been a shift away from Latin roots in the formation of element names, the shift is not toward English roots but rather to a wide variety of essentially accidental variables.
NOTE: If you want to know more about the elements and their names, I recommend the following website, from which I gathered much of the information in my answer: http://www.vanderkrogt.net/elements/.
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