Atomic number 60

Neodymium

Nd
+ phase
− phase

Shells Orbitals 4f 6s

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60 electrons in 6 shells: 2, 8, 18, 22, 8, 2.

Shells are a teaching model: an electron does not travel on a ring at a fixed distance.

Category: Lanthanide
Period: 6
Block: f
Standard atomic weight: 144.24(1) Da
Electron configuration: [Xe] 4f⁴ 6s²
Phase at 25 °C: solid
Melting point: 1024 °C
Boiling point: 3074 °C
Density: 7.01 g/cm³
Electronegativity (Pauling): 1.14
Discovered: 1885, Carl Auer von Welsbach

Neighbours in the table

Pr Pm

For 44 years neodymium hid inside a substance chemists took for an element. In 1841 Carl Gustav Mosander drew a rose-coloured oxide from the mineral cerite and named its element didymium, the twin. The name marked an inseparable twin brother of lanthanum, in Los Alamos’s words, or its similarity to lanthanum, in the history by CIAAW, IUPAC’s atomic-weights commission.

In 1885 the Austrian Carl Auer von Welsbach split didymium in two. He used repeated fractionation of ammonium didymium nitrate, separating the salt bit by bit over many rounds of crystallisation. He named one part neodymium, the new twin, and the other praseodymium; their salts differed in colour, Los Alamos notes.

Sixty electrons fill neodymium’s shells as 2, 8, 18, 22, 8 and 2, written [Xe] 4f⁴ 6s². In Jefferson Lab’s listing its oxidation state is +3, the charge an atom would hold with fully ionic bonds. Los Alamos also gives neodymium states of +4 and +2.

The metal’s bright silvery lustre does not last. Neodymium tarnishes quickly in air. Its oxide flakes off and bares fresh metal to attack, so the metal is kept under mineral oil or sealed in plastic, Los Alamos notes. Praseodymium, next door, resists corrosion in air somewhat better. Heated past 863 °C, the metal’s atoms rearrange into a different crystal packing, Los Alamos reports.

Where it is found

Neodymium makes up an estimated 41.5 milligrams of each kilogram of the Earth’s crust in Jefferson Lab’s figures, while seawater holds about 2.8 × 10⁻⁶ milligrams per litre. It occurs in monazite and bastnasite, the principal sources of the rare-earth metals on Los Alamos’s page. Monazite sand has the formula (Ce, La, Th, Nd, Y)PO₄ in Jefferson Lab’s account, a phosphate carrying neodymium alongside cerium, lanthanum, thorium and yttrium.

Praseodymium and neodymium compounds were produced in California in 2023 and 2024, the US Geological Survey reports, where bastnaesite was mined as a primary product at Mountain Pass.

Natural neodymium is a mix of seven isotopes. In CIAAW’s mole fractions, neodymium-142 is the commonest of them at 27.2 per cent of atoms, ahead of neodymium-144 at 23.8 per cent and neodymium-146 at 17.2 per cent. The heaviest, neodymium-150, makes up 5.6 per cent. The Atomic Mass Data Center lists nuclides from neodymium-124 to neodymium-163.

Why it matters

Neodymium tints glass in delicate shades from pure violet through wine-red to warm grey, Los Alamos reports, and such glass lets light through with unusually sharp absorption bands. Astronomers have used those bands to calibrate spectral lines. Neodymium also cancels the green that iron impurities give glass, in Jefferson Lab’s account, and didymium glass, the old twin mixture, goes into goggles for welders and glass blowers. Glass containing neodymium can serve as a laser material producing coherent light, and some of its salts colour enamels and glazes.

Neodymium makes up about 18 per cent of misch metal, the alloy behind lighter flints, according to Jefferson Lab. Neodymium-iron-boron magnet block appears, with neodymium-praseodymium oxide and samarium-cobalt alloy, among the potential stockpile acquisitions for fiscal 2024 and 2025 in the US Geological Survey’s report. Neodymium-iron-boron alloys can also stand in for cobalt in magnets. Neodymium oxide of at least 99.5 per cent purity rose from 49 dollars a kilogram in 2020 to 134 in 2022, then fell to an estimated 56 in 2024.

One natural isotope opens a route to another element. Neodymium-146 captures a neutron to become neodymium-147, which beta-decays to promethium-147, in IUPAC’s isotope table on PubChem’s record. That product, whose half-life is 2.6 years, serves as a radioactive power source.

Properties

Properties of neodymium Standard atomic weights from IUPAC/CIAAW (abridged, 2024); other values from PubChem's periodic table, kelvin converted to °C.
Property	Value	Unit	Source
Atomic number	60
Standard atomic weight	144.24(1) Da	Da	IUPAC/CIAAW 2024
Melting point	1024 °C	°C	Los Alamos: 1024 °C
Boiling point	3074 °C	°C	Los Alamos: 3074 °C
Density	7.01 g/cm³	g/cm³
Electronegativity (Pauling)	1.14
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f⁴
Phase at 25 °C	solid

Safety

Most company reports to the European Chemicals Agency, 56.4% of 463, find that neodymium meets no hazard criteria under the Globally Harmonized System (GHS). Others give it the signal word Danger: a flammable solid (34.3%), self-heating and liable to catch fire (33.3%), and a skin and serious eye irritant (41.9% each). The metal carries a low-to-moderate acute toxic rating from Los Alamos, and its salts are eye irritants in Haz-Map’s summary. Classification and handling guidance are in the PubChem Laboratory Chemical Safety Summary for neodymium.

Questions

Why is neodymium called the new twin?

Its name joins the Greek neos, new, to didymos, twin, in the history by CIAAW on PubChem's record. Mosander had found lanthanum only two years before he named didymium, the older twin, for its likeness to it. CIAAW's record shows the element's atomic weight rising from 143.6 in 1902 to 144.24 by 1961.

Is neodymium radioactive?

Two of the seven isotopes in natural neodymium decay, but extremely slowly. Neodymium-144, near a quarter of natural atoms, emits alpha particles with a half-life of 2.29 × 10¹⁵ years in the evaluation of the International Atomic Energy Agency (IAEA). A half-life is the time for half of a sample to decay. Neodymium-150 undergoes double beta decay, with a half-life of 9.3 × 10¹⁸ years on PubChem's nuclide table.

How is neodymium used to date rocks?

Samarium-147 (half-life 1.073 × 10¹¹ years, IAEA) decays into neodymium-143, so the ratio of neodymium-143 to neodymium-144 dates rocks over long spans, in IUPAC's isotope table on PubChem's record. A slight excess of neodymium-142 in billion-year-old Greenland rocks came from short-lived samarium-146 (6.8 × 10⁷ years, IAEA), in IUPAC's table. That parent had little time to enter the minerals before it decayed, which is evidence that Earth's crust formed before the planet was 100 million years old.

How is neodymium metal produced?

Neodymium salts are parted from other rare earths through ion-exchange or solvent-extraction methods, on Los Alamos's page, and an anhydrous halide such as neodymium fluoride, NdF₃, is then reduced with calcium metal. Auer von Welsbach had separated the element's compounds in 1885, yet the metal was not obtained in relatively pure form until 1925. Other separation methods also work, Los Alamos adds.