Scandium · element 21
Predicted by Mendeleev before anyone found it, now hidden in aluminium bike frames and stadium floodlights
Key facts
Scandium is the element that helped prove the periodic table worked. In 1869 Dmitri Mendeleev left a gap below boron and above yttrium and predicted the properties of the missing element, which he called ekaboron. Ten years later a Swedish chemist found it, and its atomic weight, the formula of its oxide and the behaviour of its salts matched the prediction closely.
Despite that famous start, scandium remains obscure. It is not rare in the Earth's crust, but it is so thinly spread that no mine exists mainly for it, and world production is measured in tens of tonnes a year. Where it is used, it punches well above its weight.
Where it is found
Scandium is about as abundant in the crust as cobalt, but it almost never concentrates into ore bodies. It is a trace component of hundreds of minerals and a major component of very few. The rare mineral thortveitite from Norway and Madagascar is one exception. Otherwise scandium is recovered as a by-product: from uranium processing, from the red mud left over when bauxite is refined into aluminium, and from the tailings of titanium and nickel operations. China and Russia supply much of the world's small output, and new projects in Australia and the Philippines aim to add to it.
Scandium is relatively more common in the Sun and some stars than in the Earth's crust, and it is easier to detect there by its spectral lines than it is to find in a rock.
How it was discovered
Lars Fredrik Nilson, working in Uppsala in 1879, was trying to purify ytterbium from the minerals euxenite and gadolinite when he isolated an oxide with unexpected properties. He named the new element scandium after Scandinavia. His colleague Per Teodor Cleve quickly pointed out that it matched Mendeleev's ekaboron. Metallic scandium was not prepared until 1937, by electrolysing molten chlorides, and quantities large enough to study properly were not available until 1960.
What we use it for
The most important use is in aluminium alloys. Adding a small fraction of a per cent of scandium produces tiny particles that pin the metal's grain structure, making it stronger, more weldable and resistant to softening when heated. Soviet MiG fighter aircraft used such alloys, and they appear today in high-end bicycle frames, baseball bats, lacrosse sticks and some aerospace parts. Cost has kept the alloys out of mass-market products.
Scandium iodide in metal-halide lamps gives a light close to daylight, which is why stadium floodlights and film sets use it. Scandium oxide stabilises the zirconia electrolyte in solid oxide fuel cells, and this could become its largest market. Scandium compounds also serve as catalysts in organic chemistry, and the radioactive isotope scandium-46 is used as a tracer in oil refineries.
Reading the numbers
Scandium melts at about 1541 °C, slightly higher than iron, and boils at about 2836 °C. Its density is 2.985 g/cm³, only a little more than aluminium and well under half that of iron, so it is a light metal with a high melting point, an unusual and valuable combination. The configuration [Ar] 3d1 4s2 marks it as the first element with an electron in a d orbital, which makes it the first transition metal. In practice it gives up all three outer electrons to form Sc3+, so it behaves more like aluminium or the rare earths than like iron or copper. Its first three ionisation energies rise steadily, 633, 1235 and 2389 kJ per mole, and then jump to over 7000 for the fourth, confirming that +3 is the only stable state. It heads group 3 at the start of the d-block, exactly where a metal with one d electron belongs.
Safety and the environment
Scandium has no known biological role and is not especially toxic, though its compounds, like many metal salts, irritate the skin and lungs and should not be swallowed. Finely divided scandium metal can ignite. The environmental questions are mostly about supply. Recovering scandium from red mud and mine tailings turns a waste problem into a resource, while digging a mine for such a dilute element would be wasteful. As fuel cells and lightweight alloys grow, so does interest in these recovery routes.
Did you know?
- Mendeleev predicted scandium in 1869 as ekaboron with an atomic weight near 44; the measured value is 44.96.
- Scandium is the lightest of all the transition metals, with a density only slightly greater than aluminium.
- Aluminium-scandium alloys were developed in the Soviet Union and used in MiG fighter aircraft before appearing in sporting goods.
- Although scandium was identified in 1879, a pure metallic sample was not produced until 1937, nearly sixty years later.
- Scandium is proportionally more abundant in the Sun than in the Earth's crust, an unusual reversal.
- Scandium triflate is a rare example of a metal catalyst that keeps working in water, which makes it useful in greener organic chemistry.
More in the transition metals
Column-mates come first, since elements in one column have outer electrons arranged in a similar way and tend to behave alike; the rest are the nearest neighbours in the family.
See all 38 transition metals on one page, or browse all 118 elements.
Frequently asked questions
What is scandium used for?
Its main uses are strengthening aluminium alloys for aircraft parts and sports equipment, giving daylight-coloured light in stadium floodlights, and stabilising the ceramic electrolyte in solid oxide fuel cells. All of these use small amounts, which suits an element in short supply.
Is scandium a rare earth element?
Chemically it is often grouped with the rare earths because, like them, it forms a +3 ion and occurs in the same minerals. Strictly it is a group 3 transition metal, and IUPAC includes it among the rare earth elements along with yttrium and the lanthanides.
Why is scandium so expensive?
Not because it is rare, but because it is spread thinly through rocks and never forms rich ores. It is recovered in small quantities as a by-product of other mining, so supply is tiny and unreliable, and the price stays high.
Is scandium a transition metal?
Yes, it is the first one. Its atom has a single electron in a 3d orbital, which places it at the start of the d-block, although it only ever uses the +3 oxidation state and so lacks the colourful, variable chemistry of metals such as iron or copper.
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Written by Anthony. Updated September 2026. Numerical data from Periodic-Table-JSON (CC BY-SA), cross-checked against the Scandium reference article. Spotted an error? Tell us.