Atomic number 71

Lutetium

Lu
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− phase

Shells Orbitals 4f 5d 6s

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71 electrons in 6 shells: 2, 8, 18, 32, 9, 2.

Shells are a teaching model: an electron does not travel on a ring at a fixed distance.

Category: Lanthanide
Period: 6
Block: d
Standard atomic weight: 174.97(1) Da
Electron configuration: [Xe] 4f¹⁴ 5d¹ 6s²
Phase at 25 °C: solid
Melting point: 1652 °C
Boiling point: 3402 °C
Density: 9.84 g/cm³
Electronegativity (Pauling): 1.27
Discovered: 1907, Georges Urbain

Neighbours in the table

Yb Hf

Lutetia, the ancient name for Paris, gives lutetium its name, according to Los Alamos and CIAAW, the atomic-weights commission of IUPAC, the International Union of Pure and Applied Chemistry. The name came from Georges Urbain, a French chemist. Chemists working on ytterbium were getting different results from the same experiments, according to Jefferson Lab’s history on PubChem’s record. Some blamed poor procedures or faulty equipment.

Urbain drew another conclusion: ytterbium was not one element but a mixture of two. The Swiss chemist Jean Charles Galissard de Marignac had named ytterbium in 1878, according to Jefferson Lab (1879 in Los Alamos’s history). In 1907 Urbain described a way to split Marignac’s ytterbium into the pair, Los Alamos reports. He called them neoytterbium, meaning new ytterbium, and lutecium. Carl Auer von Welsbach, an Austrian chemist, reached the same pair independently, Jefferson Lab says. Los Alamos gives his rival names as aldebaranium and cassiopeium.

Its configuration, [Xe] 4f¹⁴ 5d¹ 6s², fills the 4f subshell and adds one 5d electron. Los Alamos describes the metal as silvery white and relatively stable in air.

Where it is found

Jefferson Lab estimates 0.8 milligrams of lutetium in each kilogram of the Earth’s crust and 1.5 × 10⁻⁷ milligrams in each litre of seawater. Los Alamos finds traces of it in almost every mineral that contains yttrium. Monazite, a phosphate of cerium, lanthanum, thorium, neodymium and yttrium, holds about 0.003 per cent lutetium and is a commercial source. Today the element comes mainly from monazite sand by ion exchange, according to Jefferson Lab.

The metal itself is hard to make. Jefferson Lab ranks lutetium among the hardest elements to prepare, and the pure metal was isolated only in recent years, Los Alamos says. One route reduces anhydrous LuCl₃ or LuF₃, the chloride or fluoride with no water bound to it, with an alkali or alkaline earth metal.

Natural lutetium is a blend of two isotopes. Lutetium-175, the only stable one, makes up 97.414 per cent of the atoms in CIAAW’s 2024 table. Lutetium-176 supplies the other 2.586 per cent, and it is radioactive.

Why it matters

The half-life of lutetium-176, the span in which half of any sample decays, is 3.76 × 10¹⁰ years in the evaluation of the International Atomic Energy Agency (IAEA). In that evaluation every decay is beta-minus, in which the nucleus gives out an electron. The Atomic Mass Data Center gives 37.01 billion years and a positron-emission branch of 0.45 per cent, in which the nucleus gives out a positive electron. Each beta-minus decay leaves hafnium-176, in IUPAC’s notes.

In a mineral, two ratios carry the date: hafnium-176 to hafnium-177, and hafnium-176 to lutetium-176. Together they have dated minerals and rocks, IUPAC’s hafnium notes say. The long half-life lets them date some of the oldest rocks of Earth and the Solar System. With other isotope data from the oldest rocks, lutetium-hafnium ages let geologists infer Earth’s crust separated chemically within a few hundred million years of the Solar System’s first solids.

Los Alamos reports virtually no commercial uses for lutetium other than catalysis. Stable lutetium nuclides, atoms of one mass, give off pure beta radiation after activation by slow neutrons. Los Alamos says they can be used as catalysts in cracking, which splits large hydrocarbon molecules, in hydrogenation, which adds hydrogen, and in polymerisation, which builds chains. Jefferson Lab credits radioactive lutetium isotopes with the same role in cracking petroleum products.

Properties

Properties of lutetium Standard atomic weights from IUPAC/CIAAW (abridged, 2024); other values from PubChem's periodic table, kelvin converted to °C.
Property	Value	Unit	Source
Atomic number	71
Standard atomic weight	174.97(1) Da	Da	IUPAC/CIAAW 2024
Melting point	1652 °C	°C	Los Alamos: 1652 °C
Boiling point	3402 °C	°C	Los Alamos: 3402 °C
Density	9.84 g/cm³	g/cm³
Electronegativity (Pauling)	1.27
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹
Phase at 25 °C	solid

Safety

Lutetium metal is a flammable solid with the signal word Danger in 88.2% of the company reports behind its classification under the Globally Harmonized System (GHS). Another 7.8%, or 4 of 51 reports, find that it meets no hazard criteria. Like other rare-earth metals it is thought to have low toxicity, though information is still limited, Los Alamos says. The precautions are in the PubChem Laboratory Chemical Safety Summary for lutetium.

Questions

Why is lutetium not called cassiopeium?

The Austrian chemist Carl Auer von Welsbach separated the element too, earlier than the French chemist Georges Urbain and independently in CIAAW's account, or at nearly the same time in Jefferson Lab's. He named it cassiopeium after the constellation Cassiopeia. Urbain published his results before Auer, so IUPAC adopted Urbain's name in 1949, CIAAW says. In that year the spelling also changed from lutecium to lutetium, according to Los Alamos.

Is lutetium radioactive?

Natural lutetium contains one radioactive isotope. Lutetium-175, about 97.4 per cent of the atoms by Los Alamos's figure, is the only stable one. The remaining 2.6 per cent is lutetium-176, which is radioactive. Its half-life is 3.76 × 10¹⁰ years in the evaluation of the International Atomic Energy Agency (IAEA).

What is lutetium-177 used for?

Lutetium-177 has potential in radioimmunotherapy, radiation treatment carried to cancer cells by antibodies, for small, soft tumours and in medical imaging, according to IUPAC's isotope notes on PubChem's record. Its half-life is 6.6443 days in the Atomic Mass Data Center evaluation, which lists beta-minus emission for every decay.

How is lutetium used in scientific research?

Lutetium-175 has served as a yield tracer when plutonium in urine is measured by inductively coupled plasma mass spectrometry (ICP-MS), in IUPAC's notes. A yield tracer is an isotope added to a sample so that losses during the analysis can be tracked. Lutetium-176 goes into labelling experiments that count the absolute amount of a given protein inside a cell, IUPAC adds.