MeSH

An element of the rare earth family of metals. It has the atomic symbol Pr, atomic number 59, and atomic weight 140.91.

Elements of the lanthanoid series including atomic number 57 (LANTHANUM) through atomic number 71 (LUTETIUM).

Year introduced: 2002

A group of elements that include SCANDIUM; YTTRIUM; and the LANTHANOID SERIES ELEMENTS. Historically, the rare earth metals got their name from the fact that they were never found in their pure elemental form, but as an oxide. In addition, they were very difficult to purify. They are not truly rare and comprise about 25% of the metals in the earth's crust.

Year introduced: 1976

Electropositive chemical elements characterized by ductility, malleability, luster, and conductance of heat and electricity. They can replace the hydrogen of an acid and form bases with hydroxyl radicals. (Grant and Hackh's Chemical Dictionary, 5th ed)

A broad class of substances encompassing all those that do not include carbon and its derivatives as their principal elements. However, carbides, carbonates, cyanides, cyanates, and carbon disulfide are included in this class.

Year introduced: 1998

Substances that comprise all matter. Each element is made up of atoms that are identical in number of electrons and protons and in nuclear charge but may differ in mass or number of neutrons.