Lutetium

2008/9 Schools Wikipedia Selection. Related subjects: Chemical elements

71 ytterbium ← lutetium → hafnium Y ↑ Lu ↓ Lr Periodic Table - Extended Periodic Table
General
Name, Symbol, Number	lutetium, Lu, 71
Element category	transition metals
Group, Period, Block	n/a, 6, d
Appearance	silvery white
Standard atomic weight	174.967 (1)  g·mol−1
Electron configuration	Xe 6s2 4f14 5d1
Electrons per shell	2, 8, 18, 32, 9, 2
Physical properties
Phase	solid
Density (near r.t.)	9.841  g·cm−3
Liquid density at m.p.	9.3  g·cm−3
Melting point	1925  K (1652 ° C, 3006 ° F)
Boiling point	3675  K (3402 ° C, 6156 ° F)
Heat of fusion	ca. 22   kJ·mol−1
Heat of vaporization	414   kJ·mol−1
Specific heat capacity	(25 °C) 26.86  J·mol−1·K−1
Vapor pressure P(Pa) 1 10 100 1 k 10 k 100 k at T(K) 1906 2103 2346 (2653) (3072) (3663)
Atomic properties
Crystal structure	hexagonal
Oxidation states	3 (weakly basic oxide)
Electronegativity	1.27 (Pauling scale)
Ionization energies ( more)	1st:  523.5   kJ·mol−1
	2nd:  1340  kJ·mol−1
	3rd:  2022.3  kJ·mol−1
Atomic radius	175   pm
Atomic radius (calc.)	217  pm
Covalent radius	160  pm
Miscellaneous
Magnetic ordering	no data
Electrical resistivity	( r.t.) (poly) 582 nΩ·m
Thermal conductivity	(300 K) 16.4  W·m−1·K−1
Thermal expansion	( r.t.) (poly) 9.9 µm/(m·K)
Young's modulus	68.6  GPa
Shear modulus	27.2  GPa
Bulk modulus	47.6  GPa
Poisson ratio	0.261
Vickers hardness	1160  MPa
Brinell hardness	893  MPa
CAS registry number	7439-94-3
Selected isotopes
Main article: Isotopes of lutetium iso NA half-life DM DE ( MeV) DP 173Lu syn 1.37 y ε 0.671 173Yb 174Lu syn 3.31 y ε 1.374 174Yb 175Lu 97.41% 175Lu is stable with 104 neutrons 176Lu 2.59% 3.78×1010 y β- 1.193 176Hf
References

Lutetium (pronounced /ljuːˈtiːʃiəm/) is a chemical element with the symbol Lu and atomic number 71. A silvery-white rare metal, lutetium is the heaviest member of the rare-earth group. Its radioactive isotope is used in nuclear technology to determine the age of meteorites. lutetium usually occurs in association with yttrium and is sometimes used in metal alloys and as a catalyst in various processes. A strict correlation between periodic table blocks and chemical series for neutral atoms would describe lutetium as a transition metal because it is in the d-block, but it is a lanthanide according to IUPAC.

Characteristics and applications

Lutetium is a silvery white corrosion-resistant trivalent metal that is relatively stable in air. Lutetium is the heaviest and hardest of the rare earth elements. Lutetium has the highest melting point of any lanthanide, probably related to the lanthanide contraction.

This element is very expensive to obtain in useful quantities and therefore it has very few commercial uses. However, stable lutetium can be used as catalysts in petroleum cracking in refineries and can also be used in alkylation, hydrogenation, and polymerization applications.

Lutetium-176 (¹⁷⁶Lu) has been used to date the age of meteorites.

Lutetium aluminium garnet (Al₅Lu₃O₁₂) has been proposed for use as a lens material in high refractive index immersion lithography.

Lutetium-177 (¹⁷⁷Lu), when bound to Octreotate (a somatostatin analogue), is used experimentally in targeted radionuclide therapy for neuroendocrine tumours.

Cerium-doped lutetium oxyorthosilicate (LSO) is currently the preferred compound for detectors in positron emission tomography (PET.)

History

Lutetium (Latin Lutetia meaning Paris) was independently discovered in 1907 by French scientist Georges Urbain, Austrian mineralogist Baron Carl Auer von Welsbach and American chemist Charles James. All of these men found lutetium as an impurity in the mineral ytterbia which was thought by Swiss chemist Jean Charles Galissard de Marignac (and most others) to consist entirely of the element ytterbium.

The separation of lutetium from Marignac's ytterbium was first described by Urbain and the naming honour therefore went to him. He chose the names neoytterbium (new ytterbium) and lutecium for the new element but neoytterbium was eventually reverted back to ytterbium and in 1949 the spelling of element 71 was changed to lutetium.

The dispute on the priority of the discovery is documented in two articles in which Urbain and von Welsbach accuse each other of publishing results influenced by the published research of the other.

The commission on atomic mass, which was responsible for the attribution of the names for the new elements, settled the disputed in 1909 by granting priority to Urbain and adopting his names as official ones. A obvious problem with this decision was that Urbain was one of the four members of the commission.

Welsbach proposed the names cassiopium for element 71 (after the constellation Cassiopeia) and aldebaranium for the new name of ytterbium but these naming proposals where rejected (although many German scientists in the 1950s called the element 71 cassiopium).

Occurrence

Found with almost all other rare-earth metals but never by itself, lutetium is very difficult to separate from other elements. Consequently, it is also one of the most expensive metals, costing about six times as much as gold.

The principal commercially viable ore of lutetium is the rare earth phosphate mineral monazite: (Ce, La, etc.) PO₄ which contains 0.003% of the element. Pure lutetium metal has only relatively recently been isolated and is very difficult to prepare (thus it is one of the most rare and expensive of the rare earth metals). It is separated from other rare earth elements by ion exchange and then obtained in the elemental form by reduction of anhydrous LuCl₃ or LuF₃ by either an alkali metal or alkaline earth metal.

Isotopes

Naturally occurring lutetium is composed of 1 stable isotope ¹⁷⁵Lu (97.41% natural abundance) and 1 long-lived beta-radioactive isotope ¹⁷⁶Lu with a half-life of 3.78×10¹⁰ years (2.59% natural abundance). The last one is used in the radiometric dating (see Lutetium-hafnium dating). 33 radioisotopes have been characterized, with the most stable being naturally occurring ¹⁷⁶Lu, and artificial isotopes ¹⁷⁴Lu with a half-life of 3.31 years, and ¹⁷³Lu with a half-life of 1.37 years. All of the remaining radioactive isotopes have half-lives that are less than 9 days, and the majority of these have half-lives that are less than a half an hour. This element also has 18 meta states, with the most stable being ^177mLu (T_½=160.4 days), ^174mLu (T_½=142 days) and ^178mLu (T_½=23.1 minutes).

The known isotopes of lutetium range in atomic weight from 149.973 (¹⁵⁰Lu) to 183.961 (¹⁸⁴Lu). The primary decay mode before the most abundant stable isotope, ¹⁷⁵Lu, is electron capture (with some alpha and positron emission), and the primary mode after is beta emission. The primary decay products before ¹⁷⁵Lu are element 70 (ytterbium) isotopes and the primary products after are element 72 (hafnium) isotopes.

Applications

Lutetium is very expensive (upwards of $100 per gram) to obtain on useful quantities and therefore it has very few commercial uses. Some commercial applications include:

• Use as a pure beta emitter, using lutetium which has been exposed to neutron activation. A tiny amount of lutetium is added as a dopant to gadolinium gallium garnet (GGG), which is used in magnetic bubble memory devices.
• Use as a catalyst in the petroleum industry, or in organic light-emitting diodes (OLEDs).
• Research into possible uses for targeted radiotherapy for the development of new cancer therapies.
• Cerium-doped lutetium orthosilicate (Lu₂SiO₅:Ce), known as LSO, is a scintillator used mainly for Positron Emission Tomography.

Compounds

Fluoride: LuF₃, Chloride: LuCl₃, Bromide: LuBr₃, Iodide: LuI₃, Oxide: Lu₂O₃, Sulfide: Lu₂S₃, Nitride: LuN

Intermetalic compounds:

• Lutetium aluminium garnet

Precautions

Like other rare-earth metals lutetium is regarded as having a low degree of toxicity but it and especially its compounds should be handled with care nonetheless. Metal dust of this element is a fire and explosion hazard. Lutetium plays no biological role in the human body but is thought to help stimulate metabolism.