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Promethium (Pm). Diagram of the nuclear composition, electron configuration, chemical data, and valence orbitals of an atom of promethium-145 (atomic
Promethium (Pm). Diagram of the nuclear composition, electron configuration, chemical data, and valence orbitals of an atom of promethium-145 (atomic number: 61), an isotope of this element. The nucleus consists of 61 protons (red) and 84 neutrons (orange). 61 electrons (white) successively occupy available electron shells (rings). Promethium is a lanthanide in period 6, and the f-block of the periodic table. It melts at 1042 degrees Celsius. The trend across the lanthanide series arises from the failure of electrons filling an inner f-subshell (here, within the 4th ring) to shield outer (valence) electrons from increasing nuclear charge.
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Photo credit: © CARLOS CLARIVAN/SCIENCE PHOTO LIBRARY / Alamy / Afripics
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