Lutetium (symbol Lu, atomic number 71) is a chemical element belonging to the lanthanide series of the periodic table. It is classified as a transition metal and is the last element in the lanthanide series, sometimes considered a rare earth metal. Lutetium is a silvery-white, hard, dense metal with a high melting point of 1,663 °C (3,025 °F) and a boiling point of 3,402 °C (6,156 °F). The element has a hexagonal close‑packed crystal structure at ambient conditions.
Physical and Chemical Properties
- Atomic weight: 174.967 u
- Electron configuration: [Xe] 4f¹⁴ 5d¹ 6s²
- Density: 9.84 g·cm⁻³ (at 20 °C)
- Oxidation states: +3 is the most stable; +2 and +1 are observed in some compounds under specific conditions.
- Reactivity: Lutetium metal oxidizes slowly in air, forming a protective oxide layer; it reacts readily with water and acids, producing lutetium(III) salts.
Occurrence and Production
Lutetium is one of the least abundant of the lanthanides in the Earth's crust, with an average concentration of about 0.5 mg·kg⁻¹. It is typically recovered as a by‑product of the extraction of other rare earth elements, particularly from monazite and bastnäsite ores. Commercial production involves solvent extraction, ion‑exchange, or precipitation techniques to separate lutetium from other lanthanides.
Applications
- Catalysis: Lutetium compounds, especially lutetium(III) oxide (Lu₂O₃), serve as catalysts in petrochemical cracking and polymerization processes.
- Medical Imaging: Lutetium‑177, a radioisotope, is employed in targeted radionuclide therapy for certain cancers, notably neuroendocrine tumors.
- Optoelectronics: Lutetium aluminum garnet (Lu₃Al₅O₁₂, LAG) doped with cerium is used as a scintillator material in high‑energy physics detectors and PET scanners.
- Research: Lutetium is utilized in the synthesis of specialized organometallic complexes and as a standard in high‑resolution mass spectrometry.
Isotopes
Naturally occurring lutetium consists of two stable isotopes: ^175Lu (97.41 %) and ^176Lu (2.59 %). ^176Lu is weakly radioactive with a half‑life of about 3.78 × 10¹⁰ years, decaying by beta emission to hafnium‑176. Over 30 radioisotopes of lutetium have been identified, with ^177Lu being the most important for medical applications.
Safety and Handling
Elemental lutetium is considered to have low toxicity, but its salts can be irritants. Radioactive isotopes, particularly ^177Lu, require careful handling to limit radiation exposure. Standard laboratory safety protocols for metals and radioactive materials apply.
Historical Context
Lutetium was first isolated in 1907 by Swedish chemist Georges Urbain, who named it after “Lutetia,” the Latin name for Paris, where the research was conducted. Independent claims of discovery were also made by French chemist Carl Auer von Welsbach (who proposed the name “cassiopeium”) and the German chemist Charles James, but Urbain’s nomenclature ultimately prevailed.
