LUTETIUM



Lutetium 3503
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Lutetium

Overview

Lutetium is the heaviest, rarest, and most expensive lanthanide element. The lanthanide elements make up Row 6 of the periodic table. The periodic table is a chart that shows how chemical elements are related to one another. The lanthanides are pulled out into a separate row at the bottom of the table. They are also called the rare earth elements. That name does not fit very well for most lanthanides. They are not really so rare, only difficult to separate from each other. However, lutetium is both rare and difficult to separate from the other lanthanides.

Lutetium was first discovered in the early 1900s by two chemists working independently. It was found in a complex black mineral that had been found near the town of Ytterby, Sweden, in 1787.

Today, there are very few uses for lutetium metal.

SYMBOL
Lu

ATOMIC NUMBER
71

ATOMIC MASS
174.97

FAMILY
Lanthanide
(rare earth metal)

PRONUNCIATION
loo-TEE-she-um

Discovery and naming

In 1787, a Swedish army officer, Carl Axel Arrhenius (1757-1824), found an odd black rock outside the town of Ytterby, Sweden. He gave the rock to a chemist friend, Johan Gadolin (1760-1852), for study. That rock turned out to contain one of the most complex and most interesting minerals ever discovered: yttria. Chemists kept busy for the next century trying to figure out exactly what yttria was made of.

Eventually, they found nine new elements that had never been seen before. Separating these elements from each other was very difficult, however. The nine elements are chemically similar and all behave in nearly the same way. It is very difficult to know whether a sample of yttria contains one, two, three . . . or all nine of the elements.

In 1879 French chemist Jean-Charles-Galissard de Marignac (1817-94) announced the discovery of a new element in yttria. He called the element ytterbium. Other chemists suspected that ytterbium was really a mixture of elements. They searched for ways to separate ytterbium into simpler parts.

It took nearly thirty years to solve this puzzle. And the answer came from three laboratories at nearly the same time. The first to report his results was French chemist Georges Urbain (1872-1938). In 1907, he reported that ytterbium was not an element, but a mixture of two new elements. He called those elements neoytterbium and lutecium. The first name meant "new ytterbium." The second name comes from Lutecia, the ancient name for the city of Paris.

At nearly the same time, German chemist Karl Auer (Baron von Welsbach; 1858-1929) made the same discovery. He suggested different names for the two new elements in ytterbium. He called them cassiopeium and aldebaranium, in honor of the constellation Cassiopeia and the bright star Aldebaran. Today, some German chemists still refer to lutetium as cassiopeium.

A third chemist working on ytterbium was American chemist Charles James (1880-1926). James announced his discoveries after Urbain and Auer. Some authorities give credit for the discovery of lutetium to all three scientists.

None of these early scientists actually saw pure lutetium. Their element was a compound, usually lutetium oxide. The pure metal was isolated only quite recently.

In 1949, the spelling of the element changed from "lutecium" to "lutetium."

Physical properties

Lutetium is a silvery white metal that is quite soft and ductile. The term ductile means capable of being drawn into thin wires. It has a melting point of 1,652 °C (3,006°F) and a boiling point of 3,327° (6,021°F). Its density is 8.49 grams per cubic centimeter.

Chemical properties

Lutetium reacts slowly with water and dissolves in acids. Other chemical properties tend to be of interest only to researchers.

Occurrence in nature

Lutetium is thought to be very rare in the Earth's crust. It occurs to the extent of about 0.8 to 1.7 parts per million. That still makes it somewhat more common than better known elements such as iodine, silver, and mercury. The most common ore of lutetium is monazite, in which its concentration is about 0.003 percent.

Isotopes

There are two naturally occurring isotopes of lutetium, lutetium-175 and lutetium-176. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.

The second of these isotopes, lutetium-176, is radioactive. A radioactive isotope is one that breaks apart and gives off some form of radiation. Some radioactive isotopes occur in nature. Others can be produced by firing very small particles at atoms. These particles stick in the atoms and make them radioactive.

Fourteen artificial radioactive isotopes have also been produced. They have atomic masses of 155, 156, 167-174, and 177-180. None of these isotopes has any commercial use.

Although very rare, lutetium is still more common than iodine, silver, and mercury.

Extraction

Lutetium is the most difficult lanthanide to obtain in pure form. The usual method used begins with either lutetium fluoride (LuF 3 ) or lutetium chloride (LuCl 3 ). An active metal, such as sodium (Na) or potassium (K) is then added to LuF 3 or LuCl 3 to obtain pure lutetium. For example:

Uses

Lutetium is the most expensive lanthanide, selling for about $75 a gram. It is sometimes used as a catalyst in the petroleum industry. A catalyst is a substance used to speed up or slow down a chemical reaction. The catalyst does not undergo any change itself during the reaction. There are virtually no other uses for lutetium.

Compounds

There are no commercially important lutetium compounds.

Health effects

The health effects of lutetium are not known. In such cases, the best advice is to treat the element as if it were very toxic.



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