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Thulium (Tm). Diagram of the nuclear composition, electron configuration, chemical data, and valence orbitals of an atom of thulium-169 (atomic number
Thulium (Tm). Diagram of the nuclear composition, electron configuration, chemical data, and valence orbitals of an atom of thulium-169 (atomic number: 69), the most common isotope of this element. The nucleus consists of 69 protons (red) and 100 neutrons (orange). 69 electrons (white) successively occupy available electron shells (rings). Thulium is a lanthanide in period 6, and the f-block of the periodic table. It melts at 1545 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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