The Lanthanides, Rare Earth Elements

The lanthanides (or lanthanons) are a group of 15 elements of atomic numbers from 57 through 71 in which scandium (atomic number 21) and yttrium (atomic number 39) are sometimes included. The lanthanide series proper is that group of chemical elements that follow lanthanum in its group IIIB column position of the periodic table. Their distinguishing atomic feature is that they fill the 4f electronic subshell. Actually, only those elements with atomic numbers 58–71 are lanthanides. Most chemists also include lanthanum in the series because, although it does not fill the 4f subshell, its properties are very much like those of the lanthanides. The elements scandium and yttrium are also known as the “rare earths” because they were originally discovered together with the lanthanides in rare minerals and isolated as oxides, or “earths.” Collectively, these metals are also called rare earth elements (REEs). In comparison with many other elements, however, the rare earths are not really rare, except for promethium, which has only radioactive isotopes. Yttrium, lanthanum, cerium, and neodymium are all more abundant than lead in the earth's crust. All except promethium, which probably does not occur in nature, are more abundant than cadmium. The relative abundance and atomic numbers are provided. The more common lanthanide compounds are listed in Section 1. Scandium is a silvery white metallic chemical element, the first member of the first transition-metal series in the periodic table. The name is derived from Scandinavia, where the element was discovered in the minerals euxenite and gadolinite. In 1876, L. F. Nilson prepared about 2 g of high purity scandium oxide. It was subsequently established that scandium corresponds to the element “ekaboron,” predicted by Mendeleyev on the basis of a gap in the periodic table. Scandium occurs in small quantities in more than 800 minerals and causes the blue color of aquamarine beryl. Yttrium is one of the four chemical elements (the others are erbium, terbium, and ytterbium) named after Ytterby, a village in Sweden that is rich in unusual minerals and rare earths. Yttrium is a metal with a silvery luster and properties closely resembling those of rare earth metals. It is the first member of the second series of transition metals. Yttrium is found in several minerals and is produced primarily from the ore material xenotime. Lanthanum is a white, malleable metal; it is the first member of the third series of transition metals, and the first of the rare earths. Lanthanum is found with other lanthanides in the ore minerals monazite, bastnaesite, and xenotime, and in other minerals. It was discovered in 1839 by the Swedish chemist Carl G. Mosander. Scientists have created many radioactive isotopes of lanthanum. Keywords: cerium; chlorides; dysprosium; erbium; europium; gadolinium; kidneys; lanthanides; lanthanum; liver; lungs; monazite; neodymium; nitrates; oxides; scandium; terbium; ytterbium; yttrium