High Quality Content by WIKIPEDIA articles! Promethium is a chemical element with the symbol Pm and atomic number 61. It is notable for being the only other exclusively radioactive element besides technetium which is followed by chemical elements that have stable isotopes.The existence of promethium was first predicted by Bohuslav Brauner in 1902. During his research on the chemical properties of rare earth elements he found that the difference between neodymium and samarium is larger than between the other lanthanides. This prediction was supported in 1914 by Henry Moseley who, having discovered that atomic number was an experimentally measurable property of elements, found that no known element had atomic number 61. With the knowledge of a gap in the periodic table several groups started to search for the new element in natural environment.

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