Neodymium is a silvery lanthanide metal used widely in high-strength permanent magnets (NdFeB), lasers, and specialized glass. It tarnishes in air and forms compounds primarily in the +3 oxidation state.
The ground-state configuration is [Xe] 4f4 6s2. In most compounds, neodymium occurs as Nd3+, corresponding to the 4f3 configuration after losing three outer electrons. The partially filled 4f orbitals lead to characteristic optical and magnetic properties.
The predominant oxidation state is +3 (Nd3+), found in oxides, halides, and aqueous ions. Rarely, +2 (Nd2+) can exist in solid fluorides or when stabilized by complexing ligands, but it is unstable in water and oxidizes back to Nd3+.
Neodymium forms the intermetallic compound Nd2Fe14B, the basis of modern high-performance NdFeB magnets. These magnets exhibit very high magnetic energy density and are used in motors, headphones, hard drives, and wind turbines.
Neodymium oxidizes readily in moist air, forming a protective oxide film:
\(\mathrm{4\,Nd(s) + 3\,O_2(g) \rightarrow 2\,Nd_2O_3(s)}\)
It reacts slowly with cold water and more vigorously with hot water, releasing hydrogen gas:
\(\mathrm{2\,Nd(s) + 6\,H_2O(l) \rightarrow 2\,Nd(OH)_3(s) + 3\,H_2(g)}\)
Nd3+ compounds are typically pink to violet in color, but the hue varies depending on the ligand field and the glass or crystal host. These colors arise from f–f electronic transitions that are weakly allowed, giving narrow absorption lines useful in optical filters and lasers.
Other important applications include:
Neodymium is extracted through chemical separation of rare-earth mixtures. After digestion of ores with acid or alkali, solvent extraction and ion exchange techniques separate Nd3+ from other lanthanides based on small differences in ionic radii and complex stability. The product is converted to Nd2O3 or reduced to metal.
Neodymium ions exhibit sharp-line luminescence due to intra-4f electronic transitions that are shielded from the environment by outer 5s and 5p orbitals. This property makes Nd3+ an excellent dopant for solid-state lasers emitting at 1.06 µm (infrared region).
The lanthanide contraction is the gradual decrease in ionic size (Ln3+) across the series due to incomplete shielding by 4f electrons. In Nd, the radius is slightly smaller than in Pr, influencing crystal-field strengths, separation processes, and magnetic behavior of the compound.
Metallic Nd and its oxides have low acute toxicity, but fine powders are reactive and flammable. Inhalation of dust or fumes should be avoided. Use gloves and protective eyewear; store under mineral oil or inert gas to prevent oxidation. NdFeB magnets must be handled carefully due to their strong attraction forces.
Neodymium reacts with halogens to form trihalides, such as:
\(\mathrm{2\,Nd(s) + 3\,Cl_2(g) \rightarrow 2\,NdCl_3(s)}\)
These salts are ionic, paramagnetic, and form hydrated complexes in aqueous solution.