Atomic number 21

Scandium

Sc
+ phase
− phase

Shells Orbitals 3d 4s

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21 electrons in 4 shells: 2, 8, 9, 2.

Shells are a teaching model: an electron does not travel on a ring at a fixed distance.

Category: Transition metal
Period: 4
Group: 3
Block: d
Standard atomic weight: 44.956(1) Da
Electron configuration: [Ar] 3d¹ 4s²
Phase at 25 °C: solid
Melting point: 1541 °C
Boiling point: 2836 °C
Density: 2.99 g/cm³
Electronegativity (Pauling): 1.36
Discovered: 1879, Lars Fredrik Nilson

Neighbours in the table

Ca Ti

The 3d orbitals of the fourth period take their first electron at scandium. Because 3d fills only once 4s is full and before any electron enters 4p, scandium is [Ar] 3d¹ 4s², with shells of 2, 8, 9 and 2. Element 21 therefore opens the first transition series, the period 4 elements in which 3d is being filled.

Removing the lone 3d electron and the 4s pair leaves Sc³⁺ with 18 electrons, as many as argon holds. Jefferson Lab, on PubChem’s record, lists +3 as scandium’s oxidation state, a bookkeeping charge as if all bonds were ionic; Los Alamos adds +2 and +1. Los Alamos also calls its oxide amphoteric, meaning it reacts with acids and with bases. Electronegativity, the pull an atom exerts on electrons it shares in a bond, is 1.36 on the Pauling scale here. Values under about 2.2 generally go with metallic character.

The metal is silver-white and turns faintly yellow or pink in air, on Los Alamos’s description. It gathers a white nitride film in air, reacts with water and burns with a yellow-red flame. Even so, nitric acid mixed one to one with 48 per cent hydrofluoric acid leaves it untouched. In its chemistry scandium behaves more like yttrium and the rare-earth metals than like aluminium or titanium, Los Alamos adds.

Where it is found

Jefferson Lab puts scandium at 22 milligrams per kilogram of crust, and the US Geological Survey rates it more abundant there than lead. Los Alamos ranks it 23rd in abundance in the sun and certain stars. Seawater carries only 6 × 10⁻⁷ milligrams per litre.

Scandium has little affinity for the anions that usually gather metals into ores, so it is scattered thinly through the rock. The US Geological Survey counts more than 100 minerals holding it in small amounts. Los Alamos finds traces in over 800 mineral species. The rare mineral thortveitite, (Sc,Y)₂Si₂O₇, found in Scandinavia and Madagascar, holds it as a principal component. The blue of aquamarine beryl is said to come from scandium.

Such low concentrations mean scandium is made only as a byproduct of other ores or of old tailings. In 2024 it was recovered while refining cobalt, nickel, titanium and zirconium, China leading, and world output reached about 40 tons of oxide equivalent. The United States last produced any in 1969.

Why it matters

Mendeleev predicted an element he called ekaboron, with an atomic weight between calcium’s 40 and titanium’s 48. Lars Fredrik Nilson found scandium in 1879 while trying to purify ytterbia from 10 kilograms of euxenite, in Jefferson Lab’s account. Los Alamos names gadolinite as well. Nilson prepared about 2 grams of pure oxide from euxenite and other rare-earth residues, Los Alamos adds. In 1879 Per Theodore Cleve proved it was ekaboron, IUPAC’s atomic-weights commission (CIAAW) records. The name comes from the Latin Scandia, for Scandinavia.

Fischer, Brunger and Grienelaus first prepared the metal in 1937 by electrolysing melted chlorides, and a first pound at 99 per cent purity was announced in 1960. Los Alamos calls scandium a very light metal with a melting point far above aluminium’s, which draws the interest of spacecraft designers. In 2024 its main uses were aluminium-scandium alloys and solid oxide fuel cells, which generate electricity across a solid oxide, per the US Geological Survey.

Scandium iodide, ScI₃, goes into mercury vapour lamps so that their light closely resembles sunlight. Los Alamos ties that to indoor and night-time colour television, and counts about 20 kilograms a year of the oxide used for such lighting in the United States. Light-emitting diodes may displace these lamps, the US Geological Survey expects.

Properties

Properties of scandium Standard atomic weights from IUPAC/CIAAW (abridged, 2024); other values from PubChem's periodic table, kelvin converted to °C.
Property	Value	Unit	Source
Atomic number	21
Standard atomic weight	44.956(1) Da	Da	IUPAC/CIAAW 2024
Melting point	1541 °C	°C	Los Alamos: 1541 °C
Boiling point	2836 °C	°C	Los Alamos: 2836 °C
Density	2.99 g/cm³	g/cm³
Electronegativity (Pauling)	1.36
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹
Phase at 25 °C	solid

Safety

Scandium is classed as a flammable solid under the Globally Harmonized System (GHS). That class appears in 93.3% of company reports to the European Chemicals Agency, with the signal word Danger. Little is yet known about its toxicity, Los Alamos notes. Scandium’s classification and handling guidance are set out in the PubChem Laboratory Chemical Safety Summary for scandium.

Questions

Is scandium a rare earth element?

The US Geological Survey counts it as one of the 17 rare-earth elements. On the periodic table it sits in group 3 as a transition metal, at the head of the d block in period 4. Its chemistry, on Los Alamos's page, is closer to yttrium and the rare-earth metals than to aluminium or titanium. In thortveitite, (Sc,Y)₂Si₂O₇, the two elements even appear side by side in one formula.

Is scandium used in bicycle frames and baseball bats?

Alloys of aluminium and scandium go into aluminium baseball bats, bicycle frames and lacrosse sticks, Jefferson Lab reports on PubChem's record. Aluminium-scandium alloys were the principal use in 2024, with solid oxide fuel cells, in the US Geological Survey's summary. In high-performance scandium-alloy uses, titanium and aluminium high-strength alloys or carbon-fibre materials may substitute, the same summary adds.

How much does scandium cost and where does it come from?

Scandium is produced only as a byproduct of other ores or of old tailings, and world production in 2024 was about 40 tons of oxide equivalent, by industry estimates the US Geological Survey reports. Its 2024 price estimates were 1.20 dollars per gram for 99.99 per cent oxide and 153 dollars per gram for ingot. None is recycled, and the United States imports all it uses.

Is scandium radioactive?

Natural scandium is not. It has one stable isotope, scandium-45, which makes up all of the element found in nature, by the figures of IUPAC's atomic-weights commission (CIAAW) on PubChem's record. Scandium-46 is a beta emitter with a half-life of 83.757 days in the Atomic Mass Data Center (AMDC) table. It serves as a tracer in oil-refinery crackers, in studies of silt moving through rivers and harbours, and in research on antibodies aimed at tumour cells.