RARE EARTH ELEMENTS

Cerium, symbol Ce, soft, gray metallic element that is the most abundant of the rare earth elements. Cerium is in the lanthanide series of the periodic table. Its atomic number is 58.

Dysprosium, symbol Dy, metallic element with an atomic number of 66. Dysprosium is one of the rare earth elements in the lanthanide series of the periodic table. The element was discovered in 1886 by Paul Émile Lecoq de Boisbaudran, who separated one of its compounds from an oxide of holmium.

Dysprosium is 42nd in abundance among the elements in the earth's crust. The compounds of dysprosium are found in gadolinite, xenotime, euxenite, and fergusonite in Norway, the United States, Brazil, India, and Australia. Its salts are either yellow or yellow-green in color, the most common being a chloride (DyCl3), a nitrate (Dy(NO3)3·5H2O), and a sulfate (Dy 2(SO4)3·8H2O). The salts of dysprosium have an extremely high magnetic susceptibility. Dysprosium usually occurs as the white oxide dysprosia (Dy2O3), with erbium and holmium, two other rare earth elements.

Dysprosium melts at about 1412° C (about 2574° F), boils at about 2567° C (about 4653° F), and has a specific gravity of 8.55. The atomic weight of dysprosium is 162.50.

Metallic erbium has a bright silvery luster. Erbium oxide, Er2O 3, is a rose-red compound slowly soluble in many mineral acids, forming a series of rose-colored salts, solutions of which have a sweet, astringent taste.

Europium, symbol Eu, soft, silvery metallic element that is among the least abundant of the rare earth elements. Europium is in the lanthanide series of the periodic table; its atomic number is 63.

Gadolinium, symbol Gd, silvery white metallic element with an atomic number of 64. Gadolinium is one of the rare earth elements in the lanthanide series of the periodic table. It is named after the Finnish chemist John Gadolin.

Holmium is one of the least abundant of the rare earth metals, ranking 55th in order of abundance of the elements in the earth's crust. Holmium has an atomic weight of 164.93. It melts at about 1474° C (about 2685° F), boils at about 2700° C (about 4892° F), and has a specific gravity of 8.8. Holmium occurs in gadolinite and other minerals containing rare earths. Holmium oxide, Ho2O3, a grayish-white powder, and a few salts, such as the sulfate, have been prepared.

Lanthanum (Greek lanthanein, "to escape notice"), symbol La, metallic element with an atomic number of 57. Lanthanum is one of the rare earth elements of the periodic table. Lanthanum is often regarded as the first member of the lanthanide series, to which it gives its name.

Lanthanum was discovered by the Swedish chemist Carl Gustav Mosander in 1839. It burns in air at about 450° C (about 842° F) to form lanthanum oxide, La2 O3. It forms colorless trivalent salts, including one of the strongest trivalent bases, which is used by analytical chemists. It generally occurs with other rare earth elements in such minerals as apatite and monazite and in certain kinds of calcite and fluorspar. It is fairly common, ranking 28th in order of abundance of the elements in the earth's crust.

Lutetium, symbol Lu, silvery white metallic element with an atomic number of 71. Lutetium is one of the rare earth elements of the periodic table.

Lutetium was discovered independently by two investigators, the French chemist Georges Urbain in 1907 and the Austrian chemist Carl Auer von Welsbach about the same time. It was named by Urbain, who derived the word from Lutetia, the ancient name of Paris. Lutetium occurs in various rare earth minerals, usually associated with yttrium. It is the rarest of the rare earth elements and ranks 59th in order of abundance of the elements in the earth's crust. Several trivalent salts are known. A natural radioactive isotope of lutetium that has a half-life of about 30 billion years is used in determining the age of meteorites in relation to the age of the earth.

Neodymium, symbol Nd, silvery metallic element with an atomic number of 60. Neodymium is one of the rare earth elements in the lanthanide series of the periodic table. Neodymium was isolated in 1885 by the Austrian chemist Baron Carl Auer von Welsbach, who separated it from praseodymium. Neodymium and praseodymium had previously been regarded as a single element, called didymium. Neodymium ranks 27th in order of abundance of the elements in the earth's crust. It forms trivalent salts, which are rose-red or reddish-violet in color.

Praseodymium, symbol Pr, silvery metallic element with an atomic number of 59. Praseodymium is one of the rare earth elements in the lanthanide series of the periodic table.

Praseodymium was discovered in 1885 by the German chemist Carl Auer von Welsbach, who separated it from neodymium. A mixture of the two elements had formerly been considered a single element, called didymium. Praseodymium is a paramagnetic metal that corrodes rapidly in moist air. It forms green trivalent salts.

Samarium, symbol Sm, hard, brittle, lustrous metallic element. Samarium is one of the rare earth elements in the lanthanide series of the periodic table. The atomic number of samarium is 62.

Terbium, symbol Tb, metallic element with an atomic number of 65. Terbium is one of the rare earth elements in the lanthanide series of the periodic table.

Terbium was discovered in 1843 by the Swedish chemist Carl Gustav Mosander. It ranks about 58th in natural abundance among the elements in crustal rock. It occurs in minute quantities as a white oxide known as terbia, Tb2O3, in such minerals as gadolinite.

Thulium, symbol Tm, silver-gray metallic element that is the rarest of the rare earth elements. Thulium is in the lanthanide series of the periodic table; the atomic number of thulium is 69.

Thulium was discovered in 1879 by the Swedish chemist Per Teodor Cleve. Thulium ranks 61st in abundance among the elements in the crust of the earth and is found in small quantities in such rare earth minerals as euxenite, gadolinite, and blomstrandine. The metal can be isolated by reduction of its oxide, Tm2O3, and is soft, malleable, and ductile.

Ytterbium, symbol Yb, soft, malleable, ductile metallic element that has a bright, silvery luster. Ytterbium is one of the rare earth elements in the lanthanide series of the periodic table. The atomic number of ytterbium is 70.

In 1878, the Swiss chemist Jean Charles de Marignac separated a new substance from the rare earth elements and named it ytterbium. In 1907 and 1908, however, the French chemist Georges Urbain and the Austrian chemist Carl Auer von Welsbach independently separated Marignac's ytterbium into two elements, which are now called ytterbium and lutetium.

Yttrium was isolated by the Swedish chemist Carl Gustav Mosander in 1843. Yttrium metal can be prepared by the reduction of yttrium triflouride (YF3) with calcium. It oxidizes readily in air to the oxide Y2O3 and dissolves in hot water to form the hydroxide Y(OH)3. Yttrium ranks about 29th in abundance of the elements in the earth's crust. Yttrium is found as an oxide in most of the rare earth minerals.

Yttrium melts at about 1522° C (about 2772° F), boils at about 3338° C (about 6040° F), and has a specific gravity of 4.47. The atomic weight of yttrium is 88.906. Yttrium is sometimes included among the rare earth elements.