Lutetium (Lu)
“The last lanthanide — named after Paris, and now injected into patients as radioactive lutetium-177 to hunt down tumours.”
How its electrons are arranged
Computed from the aufbau principle, with known real-world exceptions applied automatically.
Characteristics
- Electron configuration [Xe] 4f¹⁴ 5d¹ 6s² — the fourteenth and final electron closes the 4f subshell, so lutetium ends the lanthanide row and opens the 5d transition series; its three valence electrons (5d¹ 6s²) give the familiar Lu³⁺ ion.
- The lanthanide record-holder: hardest, densest (about 9.8 g/cm³) and highest-melting (1663 °C) of the whole rare-earth family.
- Natural lutetium mixes stable lutetium-175 with radioactive lutetium-176, whose 37-billion-year half-life lets geologists date ancient rocks and meteorites by the lutetium–hafnium clock.
- One of the scarcest rare earths — the crust holds well under one part per million of it — which keeps the metal among the costliest of the lanthanides.
A silvery-white metal that is unusually hard and heavy for a rare earth — it is the densest, hardest and highest-melting of all the lanthanides. It also tarnishes only slowly, so a polished surface keeps its shine longer than most of its more reactive cousins.
Where you meet it
✦ Uses
- Targeted cancer therapy: lutetium-177 drugs such as Lutathera and Pluvicto bolt a tumour-seeking molecule onto a beta-emitting lutetium atom, delivering radiation straight into neuroendocrine and prostate tumours.
- PET-scanner detector crystals: lutetium oxyorthosilicate (LSO/LYSO) scintillators turn the arriving gamma rays into measurable flashes of light.
- LuAG (lutetium aluminium garnet) scintillators and phosphors serve in medical-imaging detectors and bright white LEDs.
- Lutetium salts work as strong Lewis-acid catalysts in petroleum refining and fine-chemical synthesis.
◍ Everyday examples
- A patient receiving Lutathera therapy at an oncology hospital carries lutetium-177 in the bloodstream for days while it homes in on tumour cells.
- Monazite — the heavy beach-sand mineral being explored along Bangladesh’s Cox’s Bazar coast — carries traces of every lanthanide, lutetium included.
- Meteorite ages reported by research groups worldwide are often pinned down by the slow decay of lutetium-176 into hafnium-176.
History & name
In 1907 three chemists independently wrested a new element out of ytterbia: Georges Urbain in Paris, Carl Auer von Welsbach in Vienna and Charles James in the USA. The Urbain–Welsbach priority fight went before an international commission, which ruled for Urbain in 1909; he crowned the element after Lutetia, the Roman town that stood where Paris now rises. James, who had spent years of patient fractional crystallisations, courteously withdrew his claim, while Welsbach’s rival name “cassiopium” lingered in German-language books for decades before fading away.