Scandium (Sc)

Ground-state configuration: \([Ar]3d^1\,4s^2\). In compounds, scandium almost always forms Sc³⁺ by losing all three valence electrons:

\(\mathrm{Sc \rightarrow Sc^{3+} + 3e^-}\)

Lower states like +2 or +1 are rare and typically unstable under normal conditions.

Sc³⁺ is d^0, so there are no d–d transitions to absorb visible light. Many Sc(III) salts therefore appear colorless; any observed color often arises from charge-transfer bands or impurities.

Scandium forms a protective oxide but reacts when heated:

• Oxidation: \(\mathrm{4\,Sc + 3\,O_2 \rightarrow 2\,Sc_2O_3}\)
• With acids (dissolves readily): \(\mathrm{2\,Sc + 6\,HCl \rightarrow 2\,ScCl_3 + 3\,H_2}\)
• In water, bulk Sc is slow at room T (oxide film), but finely divided Sc can form hydroxide: \(\mathrm{Sc^{3+} + 3\,OH^- \rightarrow Sc(OH)_3\downarrow}\)

Yes, weakly. \(\mathrm{Sc(OH)_3}\) dissolves in acids to give aquo complexes such as \([\mathrm{Sc(H_2O)_6}]^{3+}\), and in concentrated base it can form hydroxo complexes:

\(\mathrm{Sc(OH)_3 + OH^- \rightleftharpoons [Sc(OH)_4]^-}\)

Exact speciation depends on pH and concentration.

• Sc₂O₃ (scandia): ceramic, dopant in solid electrolytes and lighting.
• ScCl₃: precursor for organometallics and for Al–Sc alloy production.
• ScI₃ with NaI: used in metal-halide lamps to tune color temperature.

Small additions of Sc to Al form coherent Al₃Sc precipitates (L1₂ structure) that pin dislocations and stabilize grain structure, yielding high strength at low density and improved weldability—valuable in aerospace, additive manufacturing, and premium sports components.

Scandium does not occur as rich ores; it is recovered as a by-product from processing of rare-earth minerals, titanium/zirconium operations, and from residues such as red mud (bauxite residue). Separation uses solvent extraction/ion exchange to isolate Sc(III) from chemically similar cations.

Scandium(III) is a hard Lewis acid that prefers oxygen and nitrogen donors and commonly adopts octahedral coordination in solution, e.g. \([\mathrm{Sc(H_2O)_6}]^{3+}\). It forms hydroxo-bridged clusters upon hydrolysis at higher pH.

In metal-halide lamps, mixtures like \(\mathrm{ScI_3}\) + \(\mathrm{NaI}\) produce a bright, sun-like spectrum suitable for stadium and film lighting. Scandia-stabilized materials are also used in some high-intensity discharge lamp components.

Sc-46 (\(t_{1/2}\) ≈ 84 d) is a gamma emitter used as a tracer in pipelines and industrial studies. Emerging research explores Sc-44/Sc-47 pairs for theranostic medical applications (diagnosis + therapy) due to PET imaging and therapeutic beta emissions.