Lutetium

Lutetium is a silvery-white, dense metallic element with atomic number 71. It is the last lanthanide in the periodic table and is among the rarest naturally occurring rare-earth elements.

Lanthanide: A series of 15 metallic elements from lanthanum to lutetium, characterized by filling of the 4f electron shell. Lutetium is the series’ final element, though its placement with the lanthanides has a historical complication.
Lutetium-177: A radioactive lutetium isotope used in targeted radionuclide therapy for certain cancers. This isotope delivers beta radiation to tumors when attached to molecules that bind cancer cells.
Georges Urbain: A French chemist who identified lutetium in 1907 while studying ytterbia. Urbain’s work established one of the competing claims to the element’s discovery.
Lawrencium: A radioactive synthetic element with atomic number 103, placed at the end of the actinide series. Like lutetium among lanthanides, lawrencium’s position at an f-block boundary is debated.
Atomic number: The number of protons in an atom’s nucleus, which determines the element’s identity. Lutetium’s 71 protons distinguish it from every other element.
Lutetium oxyorthosilicate: A lutetium-containing scintillator crystal used to detect gamma rays in positron emission tomography scanners. Its dense, fast-scintillating crystals help PET scanners detect annihilation photons.
Carl Auer von Welsbach: An Austrian chemist who independently separated ytterbium into ytterbium and cassiopeium, later called lutetium. His independent discovery led to a priority dispute with Urbain.
Yttrium: A metallic element with atomic number 39, chemically similar to the lanthanides but outside their series. Yttrium is grouped with rare earths despite not being a lanthanide, highlighting the difference between chemical grouping and table position.
Electron configuration: The arrangement of electrons among an atom’s energy levels and orbitals. Its filled 4f shell helps distinguish lutetium’s chemistry from that of earlier lanthanides.
Lutetium aluminum garnet: A crystalline material used as a laser host and in optical and scintillation applications. Lutetium’s heavy ions contribute to the useful optical and radiation-detection properties of this garnet.

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Group 3 elementBroader topic: Some periodic-table conventions place it below yttrium in Group 3.