Sc · Element 21 · Transition metal
Scandium (Sc) is element 21, a silvery solid metal in group 3 and period 4. A neutral atom has 21 protons and 21 electrons, with the ground-state configuration [Ar] 3d¹ 4s². [1] [2]
Answers
Scandium is solid at 20 °C. Its melting point is about 1541 °C and its density is about 2.99 g/cm³. It belongs to the transition metals, not the halogens or noble gases. [1]
Scandium is also commonly included among the rare-earth elements, together with yttrium and the lanthanides. That industrial grouping does not change its group 3 position in the periodic table. [5]
Neutral scandium has the configuration [Ar] 3d¹ 4s². Its shell populations are 2, 8, 9 and 2, so four principal shells are occupied. The outermost shell contains two electrons, while the usual three-electron valence description also counts the 3d electron. [2]
The common +3 oxidation state is consistent with losing those three electrons. The resulting Sc³⁺ ion has 18 electrons and the argon configuration. Outermost-shell electrons and chemically involved valence electrons are not always the same count for a transition metal. [1] [3]
Metallic scandium can be added to aluminium alloys, including alloys used in aerospace and sporting equipment. Scandium iodide is a compound used in certain high-intensity lamps. These are different materials and applications, not uses of a lump of pure scandium for lighting. [1]
Lars Fredrik Nilson discovered scandium in 1879. Per Teodor Cleve recognized it as Mendeleev’s predicted eka-boron. The name refers to Scandinavia. [4]
Natural scandium is monoisotopic: its stable isotope is Sc-45. That atom has 21 protons and 24 neutrons, because 45 minus 21 is 24. Other, radioactive scandium isotopes exist. [4] [1]
Structure
Not a diagram of dots on rings — a Monte-Carlo sample of the actual probability density |ψ|² for each occupied subshell. Drag to rotate. Blue and violet mark opposite signs of the wavefunction, which is what makes bonding possible.
Measured values
Every bar shows where scandium sits among all 118 elements for that property.
Sources: IUPAC 2021 standard atomic weights · CRC Handbook of Chemistry and Physics · NIST. Values marked ~ are predicted rather than measured.
Same element, different neutrons
All scandium atoms have the same number of protons, 21, and differ only in their number of neutrons: those variants are its isotopes. The most common, Sc-45, has 24 neutrons and makes up 100% of natural scandium.
| ISOTOPE | Neutrons | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|---|
| Sc-45 most common | 24 | 100% | Stable | — |
Here the classroom shortcut, rounded atomic mass (44.956) minus atomic number, gives the same answer: 24.
Data: IAEA Nuclear Data Section, LiveChart of Nuclides, ground-state evaluations, retrieved October 10, 2026. Abundance is the share of atoms in the natural element; a dash means the isotope has no standard natural abundance.
Size, to scale
Radius 162 pm — that is 0.162 nm, so about 3.09 million of them side by side would span a millimetre.
Thermal range
Scandium is liquid over a 1295 K window, from 1814 K to 3109 K.
The story
Scandium is element 21, a silvery transition metal in group 3 and period 4. It is solid at 20 °C and melts at about 1541 °C. It is also included with yttrium and the lanthanides in the rare-earth grouping. [1] [5]
The neutral atom has the configuration [Ar] 3d¹ 4s². There are two outermost-shell electrons and three valence electrons when the 3d electron is counted. The common Sc³⁺ ion has the argon configuration. Natural scandium consists of stable Sc-45. [2] [3] [4]
When Dmitri Mendeleev developed his periodic table, he left a gap between calcium and titanium and predicted an element he called eka-boron, with an atomic weight between theirs and an oxide of the formula Eb₂O₃.
In 1879 the Swedish chemist Lars Fredrik Nilson, analyzing the rare minerals euxenite and gadolinite from Scandinavia, found a new oxide whose spectrum matched no known element. He named the element scandium, after Scandinavia.
Later in 1879 Per Teodor Cleve showed that scandium had the properties Mendeleev had predicted for eka-boron. Together with gallium (1875) and germanium (1886), it was one of the first confirmations of the periodic table.
Metallic scandium was first produced in 1937, by electrolysis of a molten mixture of potassium, lithium and scandium chlorides. Industrial use began only in the 1970s and 1980s, when its effect on aluminum alloys was found.
Applications
The main use of scandium metal is in aluminum alloys. Adding a few tenths of a percent of scandium refines the grain of the aluminum, making it stronger and easier to weld. These alloys are used in aerospace parts and in high-end sports equipment such as bicycle frames and baseball bats. The high price of scandium keeps them a specialty material.
Few people handle scandium knowingly. You are most likely to meet it in premium sports goods with aluminum-scandium frames or tubes, such as bicycles, baseball and softball bats and some lightweight revolver frames, and in the bright white light of stadium and television lighting that uses metal halide lamps.
Where it comes from
22 mg/kg of Earth's crust · more abundant than 74% of elements
Scandium is not especially rare: Earth's crust holds about 22 parts per million, more than lead or tin. Scandium ore is rare, though, because the element seldom concentrates. Its ions take the place of iron, magnesium and aluminum in common minerals, so it stays widely dispersed.
Scandium-rich minerals, such as thortveitite, (Sc,Y)₂Si₂O₇, found in Norway and Madagascar, are very rare. Most scandium is instead recovered as a byproduct.
World production was only about 80 tonnes of scandium oxide in 2025, all of it a byproduct, mainly of nickel and titanium processing and of old tailings and residues; China produces the most, and scandium from nickel ore in the Philippines is refined in Japan (USGS). Research also targets red mud, the residue of alumina refining.
Handling
Scandium has no known biological role, and its toxicity has not been studied in depth. Scandium metal and its compounds are generally treated as of low toxicity, but their dusts can irritate the eyes, skin and lungs, and some compounds, such as scandium chloride, are irritants.
Solid scandium is stable in air, where it forms a thin oxide layer. Fine powder or turnings can ignite, and the metal reacts with acids to release flammable hydrogen.
Sources checked .
Physical state at 20 °C, melting point, approximate density, group and period, common oxidation state, alloy and iodide-lamp applications.
Neutral Sc configuration. Shell populations are counted from the occupied subshells.
Sc IV, the spectroscopic designation of Sc³⁺, has the closed-shell argon configuration.
Natural monoisotopic Sc-45, standard atomic weight and discovery history. Neutron count is mass number minus atomic number.
Includes scandium and yttrium with the 15 lanthanides in the 17 rare-earth elements.