Matter & Energy


Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.

Praseodymium

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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 (see Magnetism) metal that corrodes rapidly in moist air. It forms green trivalent salts.

Praseodymium is widely distributed in nature and ranks 37th in order of abundance of the elements in the crust of the earth. It is found in cerite and other rare earth minerals. It is used, with small amounts of other rare earth metals, in magnesium alloys and in misch metal, an alloy used for cigarette-lighter flints and as a deoxidizer in alloys and vacuum tubes. A mixture of praseodymium and neodymium is used to tint goggles for welders.

Praseodymium melts at about 931° C (1708° F), boils at about 3520° C (about 6368° F), and has a specific gravity of 6.64. The atomic weight of praseodymium is 140.9.