Lutetium

Lutetium (English: Lutetium, symbol: Lu) is a chemical element with atomic number 71. It is the heaviest of the lanthanide series, a group of elements known as the rare earth elements. In its natural state, it is a silvery-white, hard metal that oxidizes gradually in air.

Lutetium occurs in the earth's crust in minute quantities and is usually found alongside other lanthanides in minerals such as monazite and bastnäsite. Its extraction is costly because its chemical properties are very similar to those of the neighbouring lanthanides, requiring specialized separation methods known as ion exchange or solvent extraction.

History of Discovery

Lutetium was identified between 1907 and 1908, when different scientists working independently separated it from the element then known as ytterbia. Among those credited are the French scientist Georges Urbain and the Austrian scientist Carl Auer von Welsbach. The name 'lutetium' derives from 'Lutetia', the former Latin name for Paris.

Physical and Chemical Properties

Lutetium is one of the hardest and densest of the lanthanides. It has a higher melting point and boiling point than other lanthanides. Its most common oxidation state is +3, so most of its compounds contain Lu(III), such as lutetium oxide (Lu₂O₃). Unlike some other lanthanides, Lu(III) has no unpaired 4f electrons, making it colourless and non-paramagnetic.

Isotopes

The stable naturally occurring isotope is Lu-175, which makes up the majority of naturally occurring lutetium. Lu-176 also occurs naturally and has an extremely long half-life. The decay of Lu-176 to hafnium is used in a dating method known as the Lu-Hf system, which geologists employ to determine the age of rocks and early crustal material.

Applications

Commercial use of lutetium is limited due to its high cost. Its compounds are used as catalysts in petroleum cracking in refineries, and lutetium oxyorthosilicate (LSO), a scintillating crystal used in medical imaging devices called PET scanners. The radioactive isotope Lu-177 is used to treat certain types of tumours, particularly neuroendocrine tumours, when bound to targeted molecules.