Praseodymium

Praseodymium is a soft, silvery lanthanide with the configuration [Xe] 4f3 6s2. Like most lanthanides it forms compounds mainly in the +3 state, and Pr^3+ ions have two 4f electrons whose electronic transitions absorb specific wavelengths of light. That is why praseodymium salts are leek-green in solution. The 4f orbitals are buried beneath filled 5s and 5p shells, so they barely interact with neighbouring atoms, and the absorption bands are unusually sharp. Praseodymium can also reach +4 in some solid oxides, as in its stable black oxide, Pr6O11.

Praseodymium is chemically so similar to its neighbour neodymium that the two were long thought to be a single element. Today its main use is alongside neodymium in rare-earth permanent magnets, where praseodymium can substitute for part of the neodymium in Nd-Fe-B alloys. Praseodymium-doped zircon is the bright 'praseodymium yellow' used in ceramic glazes. Didymium glass, containing praseodymium and neodymium, absorbs the intense yellow light of hot sodium, which is why glassblowers wear didymium goggles. Praseodymium also strengthens magnesium alloys used in aircraft engines.

Discovery

In 1841 Carl Gustaf Mosander extracted from cerium an earth he called didymium, from the Greek didymos, 'twin', because it seemed inseparable from lanthanum. In 1885 the Austrian chemist Carl Auer von Welsbach showed that didymium was itself a mixture. By repeated fractional crystallization of ammonium didymium nitrate, he separated it into praseodymium, the 'green twin' (Greek prasios, leek-green), and neodymium, the 'new twin'. Pure praseodymium metal was first made in 1931.