1s² 2s²p⁶ 3s²p⁶d¹⁰ 4s²p⁶d¹⁰f⁴ 5s²p⁶ 6s²

History

Neodymium, Greek neos + didymos (new twin).   In 1841, Mosander, extracted from cerite a new rose-colored oxide, which he believed contained a new element.  He named the element didymium, as it was an inseparable twin brother of lanthanum.  In 1885 Baron Carl Auer von Welsbach, an Austrian chemist,  separated didymium into two new elemental components, neodymia and praseodymia, by repeated fractionation of ammonium didymium nitrate by means of spectroscopic analysis..  While the free metal is in misch metal, long known and used as a pyrophoric alloy for light flints, the element was not isolated in relatively pure form until 1925. 

Neodymium is frequently misspelled as neodynium.  Today, neodymium is primarily obtained through an ion exchange process of monazite sand (Ce,La,Th,Nd,Y)PO₄, a material rich in rare earth elements, and through electrolysis of its halide salts.

Characteristics

The silvery-white metal oxidizes easily in air and reacts with water, displacing hydrogen gas.  Although another of the "rare" earth metals, neodymium is actually more abundant than many better known metals such as gold, silver, tin and lead.  Neodymium quickly tarnishes in air.  The tarnishing forms an oxide layer that falls off, which exposes the metal to further oxidation.  Although a "rare earth metals," it constitutes 38 ppm of Earth's crust.

It is present in the minerals monazite and bastnasite, which are principal sources of rare-earth metals.  The element may be obtained by separating neodymium salts from other rare earths by ion-exchange or solvent extraction techniques, and by reducing anhydrous halides such as NdF₃ with calcium metal.  Other separation techniques are possible.  Neodymium exists in two allotropic forms, with a transformation from a double hexagonal to a body-centered cubic structure taking place at 863^oC.

Misch metal, used in lighter flints, is about 18% neodymium. The element is also used in the manufacture of artificial rubies for laser applications.

Occurrence

Neodymium is never found in nature as the free element; rather, it occurs in ores such as monazite sand (Ce,La,Th,Nd,Y)PO₄ and bastnasite (Ce,La,Th,Nd,Y)(CO₃)F that contain small amounts of all the rare earth metals. Neodymium can also be found in Misch metal; it is difficult to separate it from other rare earth elements.

Applications

Neodymium makes up about 18% of Misch metal, a material that is used to make flints for lighters. Neodymium is also a component of didymium glass, which is used to make certain types of welder's and glass blower's goggles. Neodymium is added to glass to remove the green color caused by iron contaminants.  It can also be added to glass to create violet, red or gray colors.  Some types of glass containing neodymium are used by astronomers to calibrate devices called spectrometers and other types are used to create artificial rubies for lasers. Some neodymium salts are used to color enamels and glazes.

• Neodymium colours glass in delicate shades ranging from pure violet through wine-red and warm grey. Light transmitted through such glass shows unusually sharp absorption bands; the glass is used in astronomical work to produce sharp bands by which spectral lines may be calibrated. Neodymium is also used to remove the green colour caused by iron   contaminants from glass.
• Neodymium is used in the strongest permanent magnets known - Nd₂Fe₁₄B.   These magnets are cheaper, lighter, and stronger than samarium-cobalt magnets.   Neodymium magnets appear in high-quality products such as microphones, professional loudspeakers, in-ear headphones and computer hard disks where low mass, small volume, or strong magnetic fields are required.
• Probably because of similarities to Ca²⁺, Nd³⁺ has been reported to promote plant growth. Rare earth element compounds are frequently used in China as fertilizer. 
• Size and strength of volcanic eruption can be predicted by scanning for neodymium isotopes.  Small and large volcanic eruptions produce lava with different neodymium isotope composition. From the composition of isotopes, scientists predict how big the coming eruption will be, and use this information to warn residents of the intensity of the eruption.
• Certain transparent materials with a small concentration of neodymium ions can be used in lasers as gain media for infrared wavelengths (1054-1064 nm), e.g. Nd: YAG (yttrium aluminium garnet), Nd:YLF (yttrium lithium fluoride), Nd:YVO₄ (yttrium orthovanadate), and Nd:glass. The current laser at the UK Atomic Weapons Establishment (AWE), the HELEN 1-TW neodymium-glass laser, can access the midpoints of pressure and temperature regions and is used to acquire data for modeling on how density, temperature and pressure interact inside warheads. HELEN can create plasmas of around 10⁶K, from which opacity and transmission of radiation are measured.
• Neodymium glass (Nd:Glass) solid-state lasers are used in extremely high power (terawatt scale), high energy (megajoules) multiple beam systems for inertial confinement fusion.   Nd:Glass lasers are usually frequency tripled to the third harmonic at 351 nm in laser fusion devices.

Compounds

Neodymium compounds include

Isotopes

Naturally occurring Neodymium is composed of 5 stable isotopes,  ¹⁴²Nd, ¹⁴³Nd, ¹⁴⁵Nd, ¹⁴⁶Nd and ¹⁴⁸Nd, with ¹⁴²Nd being the most abundant (27.2% natural abundance), and 2 radioisotopes,  ¹⁴⁴Nd and ¹⁵⁰Nd. In all, 31 radioisotopes of Neodymium have been characterized, with the most stable being ¹⁵⁰Nd with a half-life (T_½) of >1.1×10¹⁹ years, ¹⁴⁴Nd with a half-life of 2.29×10¹⁵ years, and ¹⁴⁷Nd with a half-life of 10.98 days. All of the remaining radioactive isotopes have half-lives that are less than 3.38 days, and the majority of these have half-lives that are less than 71 seconds. This element also has 4 meta states with the most stable being ¹³⁹Nd^m (T_½ 5.5 hours), ¹³⁵Nd^m (T_½ 5.5 minutes) and ¹⁴¹Nd^m (T_½ 62.0 seconds).

The primary decay mode before the most abundant stable isotope, ¹⁴²Nd, is electron capture and the primary mode after is beta minus decay.  The primary decay products before ¹⁴²Nd are element Pr (praseodymium) isotopes and the primary products after are element Pm (promethium) isotopes.

Precautions

Neodymium has a low-to-moderate acute toxic rating; however its toxicity has not been thoroughly investigated. As with other rare earths, neodymium should be handled with care.   The metal should be kept under light mineral oil or sealed in a plastic material.

Neodymium dust and salts are very irritating to the eyes and mucous membranes, and moderately irritating to skin.  Breathing the dust can cause lung embolisms, and accumulated exposure damages the liver.

Neodymium metal dust is a combustion and explosion hazard.  Neodymium also acts as an anticoagulent, especially when given intravenously.

Neodymium magnets have been tested for medical uses such as magnetic braces and bone repair, but biocompatibility issues have prevented widespread application.