Lutetium
Lutetium is a chemical element with symbol Lu and atomic number 71. It is a silvery white metal, which resists corrosion in dry, but not in moist air. It is considered the first element of the 6th-period transition metals and the last element in the lanthanide series, and is traditionally counted among the rare earths.
Identity
- Atomic mass
- 174.967 u
- Category
- Lanthanides
- Group
- 3
- Period
- 6
- Block
- d
- Oxidation States
- +3
- Phase (25 °C)
- Solid
- Appearance
- silvery white
Electronic Structure
- Electron configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d1
- Short configuration
- [Xe] 4f14 5d1 6s2
- Electrons per shell
- 2, 8, 18, 32, 9, 2
- Electronegativity (Pauling)
- 1.27
- Electron affinity
- 33.4 kJ/mol
- 1st ionization energy
- 524 kJ/mol
- Ionization energies
- 524 · 1340 · 2022 · 4370 · 6445 kJ/mol
Physical properties
- Melting point
- 1651.8 °C (1925 K)
- Boiling point
- 3401.8 °C (3675 K)
- Density
- 9.841 g/cm³
- Molar heat capacity
- 26.9 J/(mol·K)
Chemical behavior of lutetium
Lutetium has fifteen outer electrons ([Xe] 4f¹⁴ 5d¹ 6s²) and almost always acts as +3, with low electronegativity (1.27). It is the densest, hardest and highest-melting lanthanide, and forms highly ionic bonds. It oxidizes slowly in dry air. Its Lu³⁺ ions are ideal as a scintillator matrix and as the platform of therapeutic Lu-177.
Reactivity
4 Lu + 3 O₂ → 2 Lu₂O₃
In dry air it tarnishes slowly with a white oxide; in moist air the corrosion progresses. When heated, it burns to the oxide.
2 Lu + 6 H₂O → 2 Lu(OH)₃ + 3 H₂
It reacts slowly when cold and vigorously when hot, releasing hydrogen. The LSO crystals that contain it are insoluble and stable.
2 Lu + 6 HCl → 2 LuCl₃ + 3 H₂
It dissolves in acids giving colorless lutetium(III) salts. The chloride is the route to Yb-176 targets that generate Lu-177.
Lu + 3 F₂ → 2 LuF₃
With fluorine it gives the fluoride, a precursor of scintillator crystals and high-density optical materials.
Notable compounds
| Compound | Formula | Use or importance |
|---|---|---|
| Lutetium oxyorthosilicate | Lu₂SiO₅ | PET detectors (LSO/LYSO) |
| Lutetium oxide | Lu₂O₃ | Scintillators and catalysts |
| Lutetium-177 chloride | ¹⁷⁷LuCl₃ | Targeted radiotherapy |
| Lutetium fluoride | LuF₃ | Optics and laser materials |
| Lutetium tantalate | LuTaO₄ | X-ray scintillators |
Electron shell distribution
View in the atom builderIsotopes
Natural lutetium combines lutetium-175 (¹⁷⁵Lu, ~97.4%), stable, and lutetium-176 (¹⁷⁶Lu, ~2.6%), a primordial radionuclide with a very long half-life used in Lu-Hf dating. Lutetium-177 (¹⁷⁷Lu, 6.6 days) emits beta and gamma and is the leading player in radioligand therapy against tumors.
Occurrence and production
It is the scarcest stable lanthanide together with thulium, at about 0.5 ppm, in monazite, bastnasite and xenotime. It does not form minerals of its own. It is obtained by acid dissolution and extremely fine chromatographic separation, and the metal by electrolysis or reduction with calcium.
History and origin of the name
Georges Urbain separated it in 1907 from Marignac's ytterbium and named it lutetium, after Lutetia, the Latin name of Paris; Auer claimed the same discovery as cassiopeium and the lawsuit lasted decades. The IUPAC sided with Urbain in 1949. From a Parisian curiosity it became a hero of nuclear medicine.
Applications and relevance of lutetium
Uses of the element
As a metal it is barely used free; its value lies in the dense matrix of LSO and LYSO scintillators that detect gammas in every PET scan, and in the Yb-176 target that, when irradiated, generates medical Lu-177.
Uses of its compounds
Lu-177 bound to peptides (Lutathera, Pluvicto) irradiates neuroendocrine and prostate tumors from within. The oxide catalyzes cracking and hydrogenation of high value and the tantalate forms X-ray screens.
Health, safety and environment
Biological role
It has no biological function and the metal is of low toxicity. Therapeutic Lu-177 is administered only in hospitals, with calculated doses and follow-up; PET crystals are not introduced into the body.
Safety
Metallic powder requires control as combustible dust. Lu-177 travels shielded with full traceability and monitors; the risk is radiological and is confined to the hospital environment.
Environment
Its scarcity forces extremely long separations with reagent consumption. In return, every dose diagnoses or treats cancers without surgery. Crystal and target recycling recovers lutetium and yttrium.
Frequently asked questions about Lutetium
Why is lutetium important in PET scanners?
Lutetium is part of scintillator crystals such as LSO and LYSO, used in the detectors of PET scanners. These materials convert the high-energy photons generated in the body into flashes of visible light, which the equipment turns into images. Their high density, detection capability and fast response allow images with good resolution to be obtained in clinically useful times.
Is lutetium dangerous?
Metallic lutetium and its non-radioactive compounds are considered of low toxicity and have no known biological function. The relevant risk comes from the isotope lutetium-177, which is radioactive and must only be handled in licensed medical facilities. The lutetium crystals of PET scanners contain a small proportion of lutetium-176, slightly radioactive, but its contribution is controlled and part of the design and calibration of the equipment.
Where does lutetium come from?
Lutetium is found in rare-earth minerals such as monazite, bastnasite and xenotime, although in very low concentrations. Its extraction requires separating it from other lanthanides through ion exchange and solvent extraction processes. Due to its relative scarcity, its high cost and the complexity of purification, it is used mainly in high-value applications such as medical imaging, radiotherapy and specialized optical materials.
What is the difference between lutetium and gadolinium in diagnostic imaging?
Gadolinium is administered to the patient as a contrast agent in magnetic resonance imaging, where it alters the signal of the tissues to improve visualization. Lutetium, by contrast, is part of the detector crystals of PET scanners and is not introduced into the body. In addition, lutetium-177 can be used therapeutically in targeted radiotherapy. They therefore have different functions: contrast in MRI, detection in PET and oncological treatment.
What is lutetium-177 used for in medicine?
Lutetium-177 is a radioactive isotope used in targeted radiotherapy, also called radioligand therapy. It binds to a molecule that recognizes receptors present in certain tumor cells and releases radiation in a localized way onto the tumor. It is used, for example, in some neuroendocrine tumors and in advanced prostate cancer. It is a specialized hospital treatment, administered under oncological and radiological protection protocols.
Why is lutetium the last lanthanide?
Lutetium closes the lanthanide series because it is element number 71 and presents the most complete electron configuration within that sequence. Although it is sometimes classified as a transition metal because of its properties, it is traditionally included at the end of the lanthanides. Its final position explains why it is one of the densest and most expensive elements of the series, with very selective applications in medicine and advanced technology.
What is lutetium used for in industrial catalysis?
Lutetium can act as a catalyst or catalytic component in specialized chemical processes such as petroleum cracking, hydrogenation, alkylation and polymerization. Its high cost prevents it from being routine in large-volume processes, but it can be justified when it improves the selectivity, stability or yield of a reaction. In practice, it is a niche catalyst reserved for industrial processes of high added value.
Main sources consulted: PubChem, Royal Society of Chemistry, NIST, IUPAC. Last revision: November 2026.