Scandium
Scandium is a chemical element with symbol Sc and atomic number 21. A silvery-white metallic d-block element, it has historically been sometimes classified as a rare earth element, together with yttrium and the lanthanoids. It was discovered in 1879 by spectral analysis of the minerals euxenite and gadolinite from Scandinavia.
Identity
- Atomic mass
- 44.956 u
- Category
- Transition metals
- Group
- 3
- Period
- 4
- Block
- d
- Oxidation States
- +3
- Phase (25 °C)
- Solid
- Appearance
- silvery white
Electronic Structure
- Electron configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d1
- Short configuration
- [Ar] 3d1 4s2
- Electrons per shell
- 2, 8, 9, 2
- Electronegativity (Pauling)
- 1.36
- Electron affinity
- 18 kJ/mol
- 1st ionization energy
- 633 kJ/mol
- Ionization energies
- 633 · 1235 · 2389 · 7091 · 8843… kJ/mol
Physical properties
- Melting point
- 1540.8 °C (1814 K)
- Boiling point
- 2835.8 °C (3109 K)
- Density
- 2.985 g/cm³
- Molar heat capacity
- 25.5 J/(mol·K)
Chemical behavior of scandium
Scandium is a group 3 transition metal ([Ar] 3d1 4s2) that loses its three outer electrons to form exclusively Sc3+, with noble-gas configuration. Its small, highly charged ion gives polarizing, partly covalent chemistry close to aluminium and yttrium, with colorless salts and a single oxidation state of +3. Fresh metal tarnishes in air and dissolves readily in acids; its oxide is basic and forms no colored compounds.
Reactivity
2 Sc + 3 Cl2 -> 2 ScCl3
Scandium reacts with chlorine forming scandium(III) chloride, a white solid that is the precursor of many scandium compounds.
2 Sc + 3 H2O (hot) -> 2 Sc(OH)3 + 3 H2
Scandium reacts with steam at high temperatures, releasing hydrogen and forming scandium hydroxide.
Notable compounds
| Compound | Formula | Use or importance |
|---|---|---|
| Scandium chloride | ScCl3 | White solid; precursor of scandium compounds, catalyst |
| Scandium(III) oxide | Sc2O3 | White solid; used in ceramic materials and lasers |
| Yttrium oxide aggregate | Y2O3 | Prepared with scandium; used in industry and phosphorescent materials |
Electron shell distribution
View in the atom builderIsotopes
Natural scandium is wholly scandium-45 (45Sc), with 24 neutrons: it is monoisotopic and stable. Scandium-46 (46Sc), with an 83.8-day half-life, is made in reactors as a radioactive tracer, but never occurs in nature.
Occurrence and production
It is a trace element (about 22 ppm) scattered in clays, micas and uranium residues, never in rich veins. It is recovered as a by-product of uranium, titanium and rare-earth refining, mainly in China, Russia and Australia. Annual world output is only a few dozen tonnes.
History and origin of the name
Lars Fredrik Nilson discovered it in 1879 analyzing euxenite and gadolinite, and named it scandium for Scandinavia. Mendeleev had predicted it as eka-boron, and its match confirmed the periodic table. Pure metal only came in the 20th century with molten-salt electrolysis.
Applications and relevance of scandium
Uses of the element
Tiny additions harden aluminium into weldable, light alloys for fighter jets, baseball bats and bike frames. Scandium-stabilized zirconia conducts ions in fuel cells.
Uses of its compounds
Scandium iodide fills metal-halide stadium lamps; oxide dopes lasers and ceramics; chloride catalyzes organic synthesis as a Lewis acid.
Health, safety and environment
Biological role
It has no biological role. Soluble salts irritate skin, eyes and airways in high doses; little is known of chronic effects for its scarcity.
Safety
Metal is fairly stable, but inorganic scandium dust requires respirators and gloves in industry. Residues go to authorized management centers.
Environment
Dispersed and scarce, its footprint comes from mining rare earths and uranium; recycling from alloy scrap is still minor.
Frequently asked questions about Scandium
Why did scandium confirm Mendeleev's table?
Because Mendeleev had predicted eka-boron with its exact properties, and Nilson's 1879 scandium matched them. That hit turned the table from clever ordering into a predictive law. Scandium was the first prediction fulfilled, before germanium and gallium completed the triumph.
What do bike frames gain from scandium?
Strength without weight: about 0.5% scandium refines aluminium grain, making frames lighter, stiffer and weldable without weakening joints. It suits racing bikes, baseball bats and fighter jets. The cost premium reserves it for top-range gear.
Why is scandium studied in organic chemistry?
Some scandium compounds act as Lewis acids: they accept electron pairs from other molecules. That ability activates reagents and eases reactions that would otherwise be slow. They are researched as catalysts for selective transformations, although usefulness depends on each reaction.
What lights do scandium lamps give?
Metal-halide lamps with scandium iodide give an intense white close to daylight, with good color rendering. They lit stadiums, studios and large spaces needing powerful light, although today they compete with more efficient LEDs.
Why is scandium so expensive?
Because it never forms rich ores: it lies scattered in traces and is only recovered as a by-product of uranium, titanium and rare earths. World output is a few dozen tonnes yearly. Small aluminium additions need little metal, but pure scandium stays a luxury for aerospace and research.
Can scandium improve fuel cells?
Yes. It can join ceramic materials used as electrolytes in solid-oxide fuel cells. Partly replacing some ions favors oxygen vacancies that ease ion movement through the ceramic. This can raise ionic conductivity, although cost and stability condition commercial use.
Why is scandium rare in everyday products?
Although it can greatly improve materials, it is used sparingly because it is costly and commercial output is tiny beside aluminium or titanium. Many uses need small but tightly controlled amounts that do not always pay off. So it appears in specialised alloys and research, not in most daily objects.
Main sources consulted: PubChem, Royal Society of Chemistry, NIST, IUPAC. Last revision: November 2026.