jan 1, 1913 - Radioactivity P3

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Frederick Soddy and Kazimierz Fajans found in 1913 that although these substances emitted different radiation, many of these substances were identical in their chemical characteristics, so shared the same place on the periodic table. They became known as isotopes.
Austrian chemist Friedrich Paneth cited a difference between real elements and simple substances , also determining that the existence of different isotopes was mostly irrelevant in determining chemical properties.

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