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Scandium, 21Sc
Scandium sublimed dendritic and 1cm3 cube.jpg
Pronunciation /ˈskændiəm/ (SKAN-dee-əm)
Appearancesilvery white
Standard atomic weight Ar°(Sc)
  • 44.955907±0.000004
  • 44.956±0.001 (abridged) [1]
Scandium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson


Atomic number (Z)21
Group group 3
Period period 4
Block   d-block
Electron configuration [ Ar ] 3d1 4s2
Electrons per shell2, 8, 9, 2
Physical properties
Phase at  STP solid
Melting point 1814  K (1541 °C,2806 °F)
Boiling point 3109 K(2836 °C,5136 °F)
Density (near r.t.)2.985 g/cm3
when liquid (at m.p.)2.80 g/cm3
Heat of fusion 14.1  kJ/mol
Heat of vaporization 332.7 kJ/mol
Molar heat capacity 25.52 J/(mol·K)
Vapor pressure
P (Pa)1101001 k10 k100 k
at T (K)16451804(2006)(2266)(2613)(3101)
Atomic properties
Oxidation states 0, [2] +1, [3] +2, [4] +3 (an  amphoteric oxide)
Electronegativity Pauling scale: 1.36
Ionization energies
  • 1st: 633.1 kJ/mol
  • 2nd: 1235.0 kJ/mol
  • 3rd: 2388.6 kJ/mol
  • (more)
Atomic radius empirical:162  pm
Covalent radius 170±7 pm
Van der Waals radius 211 pm
Scandium spectrum visible.png
Spectral lines of scandium
Other properties
Natural occurrence primordial
Crystal structure hexagonal close-packed (hcp)
Hexagonal close packed.svg
Thermal expansion α, poly: 10.2 µm/(m⋅K)(at r.t.)
Thermal conductivity 15.8 W/(m⋅K)
Electrical resistivity α, poly: 562 nΩ⋅m(at r.t., calculated)
Magnetic ordering paramagnetic
Molar magnetic susceptibility +315.0×10−6 cm3/mol(292 K) [5]
Young's modulus 74.4 GPa
Shear modulus 29.1 GPa
Bulk modulus 56.6 GPa
Poisson ratio 0.279
Brinell hardness 736–1200 MPa
CAS Number 7440-20-2
Namingafter Scandinavia
Prediction Dmitri Mendeleev (1871)
Discovery and first isolation Lars Fredrik Nilson (1879)
Isotopes of scandium
Main isotopes [6] Decay
abun­dance half-life (t1/2) mode pro­duct
44m2Sc synth 58.61 h IT 44Sc
γ 44Sc
ε 44Ca
45Sc100% stable
46Scsynth83.79 d β 46Ti
47Scsynth80.38 hβ 47Ti
48Scsynth43.67 hβ 48Ti
Symbol category class.svg  Category: Scandium
| references

Scandium is a chemical element; it has symbol Sc and atomic number 21. It is a silvery-white metallic d-block element. Historically, it has been classified as a rare-earth element, [7] together with yttrium and the lanthanides. It was discovered in 1879 by spectral analysis of the minerals euxenite and gadolinite from Scandinavia. [8]


Scandium is present in most of the deposits of rare-earth and uranium compounds, but it is extracted from these ores in only a few mines worldwide. Because of the low availability and difficulties in the preparation of metallic scandium, which was first done in 1937, applications for scandium were not developed until the 1970s, when the positive effects of scandium on aluminium alloys were discovered. To this day, its use in such alloys remains its only major application. The global trade of scandium oxide is 15–20 tonnes per year. [9]

The properties of scandium compounds are intermediate between those of aluminium and yttrium. A diagonal relationship exists between the behavior of magnesium and scandium, just as there is between beryllium and aluminium. In the chemical compounds of the elements in group 3, the predominant oxidation state is +3.


Chemical characteristics

Scandium is a soft metal with a silvery appearance. It develops a slightly yellowish or pinkish cast when oxidized by air. It is susceptible to weathering and dissolves slowly in most dilute acids. It does not react with a 1:1 mixture of nitric acid (HNO3) and 48.0% hydrofluoric acid (HF), possibly due to the formation of an impermeable passive layer. Scandium turnings ignite in the air with a brilliant yellow flame to form scandium oxide. [10]


In nature, scandium is found exclusively as the isotope 45Sc, which has a nuclear spin of 7/2; this is its only stable isotope. Twenty-five radioisotopes have been characterized with the most stable being 46Sc, which has a half-life of 83.8 days; 47Sc, 3.35 days; the positron emitter 44Sc, 4 hours; and 48Sc, 43.7 hours. All of the remaining radioactive isotopes have half-lives less than 4 hours, and the majority of these have half-lives less than 2 minutes. This element also has five nuclear isomers, with the most stable being 44m2Sc (t1/2 = 58.6 h). [11]

The known isotopes of scandium range from 36Sc to 60Sc. The primary decay mode at masses lower than the only stable isotope, 45Sc, is electron capture, and the primary mode at masses above it is beta emission. The primary decay products at atomic weights below 45Sc are calcium isotopes and the primary products from higher atomic weights are titanium isotopes. [11]


In Earth's crust, scandium is not rare. Estimates vary from 18 to 25 ppm, which is comparable to the abundance of cobalt (20–30 ppm). Scandium is only the 50th most common element on Earth (35th most abundant in the crust), but it is the 23rd most common element in the Sun. [12] However, scandium is distributed sparsely and occurs in trace amounts in many minerals. [13] Rare minerals from Scandinavia [14] and Madagascar [15] such as thortveitite, euxenite, and gadolinite are the only known concentrated sources of this element. Thortveitite can contain up to 45% of scandium in the form of scandium oxide. [14]

The stable form of scandium is created in supernovas via the r-process. [16] Also, scandium is created by cosmic ray spallation of the more abundant iron nuclei.


The world production of scandium is in the order of 15–20 tonnes per year, in the form of scandium oxide. The demand is slightly higher, [17] and both the production and demand keep increasing. In 2003, only three mines produced scandium: the uranium and iron mines in Zhovti Vody in Ukraine, the rare-earth mines in Bayan Obo, China, and the apatite mines in the Kola Peninsula, Russia.[ citation needed ] Since then, many other countries have built scandium-producing facilities, including 5 tonnes/year (7.5 tonnes/year Sc2O3) by Nickel Asia Corporation and Sumitomo Metal Mining in the Philippines. [18] [19] In the United States, NioCorp Development hopes[ when? ] to raise $1 billion [20] toward opening a niobium mine at its Elk Creek site in southeast Nebraska, [21] which may be able to produce as much as 95 tonnes of scandium oxide annually. [22] In each case, scandium is a byproduct of the extraction of other elements and is sold as scandium oxide. [23] [24] [25]

To produce metallic scandium, the oxide is converted to scandium fluoride and then reduced with metallic calcium. [26]

Madagascar and the Iveland-Evje region in Norway have the only deposits of minerals with high scandium content, thortveitite (Sc,Y)2(Si2O7), but these are not being exploited. [24] The mineral kolbeckite ScPO4·2H2O has a very high scandium content but is not available in any larger deposits. [24]

The absence of reliable, secure, stable, long-term production has limited the commercial applications of scandium. Despite this low level of use, scandium offers significant benefits. Particularly promising is the strengthening of aluminium alloys with as little as 0.5% scandium. [27] Scandium-stabilized zirconia enjoys a growing market demand for use as a high-efficiency electrolyte in solid oxide fuel cells.

The USGS reports that, from 2015 to 2019 in the US, the price of small quantities of scandium ingot has been $107 to $134 per gram, and that of scandium oxide $4 to $5 per gram. [28]


Scandium chemistry is almost completely dominated by the trivalent ion, Sc3+. The radii of M3+ ions in the table below indicate that the chemical properties of scandium ions have more in common with yttrium ions than with aluminium ions. In part because of this similarity, scandium is often classified as a lanthanide-like element. [29]

Ionic radii (pm)
Al Sc Y La Lu

Oxides and hydroxides

The oxide Sc
and the hydroxide Sc(OH)
are amphoteric: [30]

+ 3 OH
(scandate ion)
+ 3 H+
+ 3 H

α- and γ-ScOOH are isostructural with their aluminium hydroxide oxide counterparts. [31] Solutions of Sc3+
in water are acidic due to hydrolysis.

Halides and pseudohalides

The halides ScX3, where X= Cl, Br, or I, are very soluble in water, but ScF3 is insoluble. In all four halides, the scandium is 6-coordinated. The halides are Lewis acids; for example, ScF3 dissolves in a solution containing excess fluoride ion to form [ScF6]3−. The coordination number 6 is typical for Sc(III). In the larger Y3+ and La3+ ions, coordination numbers of 8 and 9 are common. Scandium triflate is sometimes used as a Lewis acid catalyst in organic chemistry. [32]

Organic derivatives

Scandium forms a series of organometallic compounds with cyclopentadienyl ligands (Cp), similar to the behavior of the lanthanides. One example is the chlorine-bridged dimer, [ScCp2Cl]2 and related derivatives of pentamethylcyclopentadienyl ligands. [33]

Uncommon oxidation states

Compounds that feature scandium in oxidation states other than +3 are rare but well characterized. The blue-black compound CsScCl3 is one of the simplest. This material adopts a sheet-like structure that exhibits extensive bonding between the scandium(II) centers. [34] Scandium hydride is not well understood, although it appears not to be a saline hydride of Sc(II). [4] As is observed for most elements, a diatomic scandium hydride has been observed spectroscopically at high temperatures in the gas phase. [3] Scandium borides and carbides are non-stoichiometric, as is typical for neighboring elements. [35]

Lower oxidation states (+2, +1, 0) have also been observed in organoscandium compounds. [36] [37] [38] [39]


Dmitri Mendeleev, who is referred to as the father of the periodic table, predicted the existence of an element ekaboron , with an atomic mass between 40 and 48 in 1869. Lars Fredrik Nilson and his team detected this element in the minerals euxenite and gadolinite in 1879. Nilson prepared 2 grams of scandium oxide of high purity. [40] [41] He named the element scandium, from the Latin Scandia meaning "Scandinavia". Nilson was apparently unaware of Mendeleev's prediction, but Per Teodor Cleve recognized the correspondence and notified Mendeleev. [42] [43]

Metallic scandium was produced for the first time in 1937 by electrolysis of a eutectic mixture of potassium, lithium, and scandium chlorides, at 700–800 °C. [44] The first pound of 99% pure scandium metal was produced in 1960. Production of aluminium alloys began in 1971, following a US patent. [45] Aluminium-scandium alloys were also developed in the USSR. [46]

Laser crystals of gadolinium-scandium-gallium garnet (GSGG) were used in strategic defense applications developed for the Strategic Defense Initiative (SDI) in the 1980s and 1990s. [47] [48]

Red giant stars near the Galactic Center

In early 2018, evidence was gathered from spectrometer data of significant scandium, vanadium, and yttrium abundances in red giant stars in the Nuclear Star Cluster (NSC) in the Galactic Center. Further research showed that this was an illusion caused by the relatively low temperature (below 3,500 K) of these stars masking the abundance signals, and that this phenomenon was observable in other red giants. [49]


Parts of the MiG-29 are made from Al-Sc alloy. Mig-29 on landing.jpg
Parts of the MiG-29 are made from Al-Sc alloy.

The addition of scandium to aluminium limits the grain growth in the heat zone of welded aluminium components. This has two beneficial effects: the precipitated Al3Sc forms smaller crystals than in other aluminium alloys, [50] and the volume of precipitate-free zones at the grain boundaries of age-hardening aluminium alloys is reduced. [50] The Al3Sc precipitate is a coherent precipitate that strengthens the aluminum matrix by applying elastic strain fields that inhibit dislocation movement (i.e., plastic deformation). Al3Sc has an equilibrium L12 superlattice structure exclusive to this system. [51] A fine dispersion of nano scale precipitate can be achieved via heat treatment that can also strengthen the alloys through order hardening. [52] Recent developments include the additions of transition metals such as zirconium (Zr) and rare earth metals like erbium (Er) produce shells surrounding the spherical Al3Sc precipitate that reduce coarsening. [53] These shells are dictated by the diffusivity of the alloying element and lower the cost of the alloy due to less Sc being substituted in part by Zr while maintaining stability and less Sc being needed to form the precipitate. [54] These have made Al3Sc somewhat competitive with titanium alloys along with a wide array of applications. However, titanium alloys, which are similar in lightness and strength, are cheaper and much more widely used. [55]

The alloy Al20Li20Mg10Sc20Ti30 is as strong as titanium, light as aluminium, and hard as some ceramics. [56]

The main application of scandium by weight is in aluminium-scandium alloys for minor aerospace industry components. These alloys contain between 0.1% and 0.5% of scandium. They were used in Russian military aircraft, specifically the Mikoyan-Gurevich MiG-21 and MiG-29. [50]

Some items of sports equipment, which rely on lightweight high-performance materials, have been made with scandium-aluminium alloys, including baseball bats, [57] tent poles and bicycle frames and components. [58] Lacrosse sticks are also made with scandium. The American firearm manufacturing company Smith & Wesson produces semi-automatic pistols and revolvers with frames of scandium alloy and cylinders of titanium or carbon steel. [59] [60]

Since 2013, Apworks GmbH, a spin-off of Airbus, have marketed a high strength Scandium containing aluminium alloy processed using metal 3D-Printing (Laser Powder Bed Fusion) under the trademark Scalmalloy which claims very high strength & ductility. [61]

Dentists use erbium-chromium-doped yttrium-scandium-gallium garnet (Er,Cr:YSGG) lasers for cavity preparation and in endodontics. [62]

The first scandium-based metal-halide lamps were patented by General Electric and made in North America, although they are now produced in all major industrialized countries. Approximately 20 kg of scandium (as Sc2 O 3) is used annually in the United States for high-intensity discharge lamps. [63] One type of metal-halide lamp, similar to the mercury-vapor lamp, is made from scandium triiodide and sodium iodide. This lamp is a white-light source with high color rendering index that sufficiently resembles sunlight to allow good color-reproduction with TV cameras. [64] About 80 kg of scandium is used in metal-halide lamps/light bulbs globally per year. [65]

The radioactive isotope 46Sc is used in oil refineries as a tracing agent. [63] Scandium triflate is a catalytic Lewis acid used in organic chemistry. [66]

The 12.4 keV nuclear transition of 45Sc has been proposed as a reference for timekeeping applications, with a theoretical precision as much as three orders of magnitude better than the current Cesium references. [67]

Health and safety

Elemental scandium is considered non-toxic, though extensive animal testing of scandium compounds has not been done. [68] The median lethal dose (LD50) levels for scandium chloride for rats have been determined as 755 mg/kg for intraperitoneal and 4 g/kg for oral administration. [69] In the light of these results, compounds of scandium should be handled as compounds of moderate toxicity. Scandium appears to be handled by the body in a manner similar to gallium, with similar hazards involving its poorly soluble hydroxide. [70]

See also

Related Research Articles

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Aluminium is a chemical element; it has symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals; about one-third that of steel. It has a great affinity towards oxygen, forming a protective layer of oxide on the surface when exposed to air. Aluminium visually resembles silver, both in its color and in its great ability to reflect light. It is soft, nonmagnetic and ductile. It has one stable isotope: 27Al, which is highly abundant, making aluminium the twelfth-most common element in the universe. The radioactivity of 26Al is used in radiometric dating.

<span class="mw-page-title-main">Barium</span> Chemical element, symbol Ba and atomic number 56

Barium is a chemical element; it has symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element.

<span class="mw-page-title-main">Calcium</span> Chemical element, symbol Ca and atomic number 20

Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to its heavier homologues strontium and barium. It is the fifth most abundant element in Earth's crust, and the third most abundant metal, after iron and aluminium. The most common calcium compound on Earth is calcium carbonate, found in limestone and the fossilised remnants of early sea life; gypsum, anhydrite, fluorite, and apatite are also sources of calcium. The name derives from Latin calx "lime", which was obtained from heating limestone.

<span class="mw-page-title-main">Dysprosium</span> Chemical element, symbol Dy and atomic number 66

Dysprosium is a chemical element; it has symbol Dy and atomic number 66. It is a rare-earth element in the lanthanide series with a metallic silver luster. Dysprosium is never found in nature as a free element, though, like other lanthanides, it is found in various minerals, such as xenotime. Naturally occurring dysprosium is composed of seven isotopes, the most abundant of which is 164Dy.

<span class="mw-page-title-main">Europium</span> Chemical element, symbol Eu and atomic number 63

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<span class="mw-page-title-main">Erbium</span> Chemical element, symbol Er and atomic number 68

Erbium is a chemical element; it has symbol Er and atomic number 68. A silvery-white solid metal when artificially isolated, natural erbium is always found in chemical combination with other elements. It is a lanthanide, a rare-earth element, originally found in the gadolinite mine in Ytterby, Sweden, which is the source of the element's name.

<span class="mw-page-title-main">Gadolinium</span> Chemical element, symbol Gd and atomic number 64

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<span class="mw-page-title-main">Lanthanum</span> Chemical element, symbol La and atomic number 57

Lanthanum is a chemical element; it has symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the eponym of the lanthanide series, a group of 15 similar elements between lanthanum and lutetium in the periodic table, of which lanthanum is the first and the prototype. Lanthanum is traditionally counted among the rare earth elements. Like most other rare earth elements, the usual oxidation state is +3, although some compounds are known with oxidation state +2. Lanthanum has no biological role in humans but is essential to some bacteria. It is not particularly toxic to humans but does show some antimicrobial activity.

<span class="mw-page-title-main">Lutetium</span> Chemical element, symbol Lu and atomic number 71

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<span class="mw-page-title-main">Terbium</span> Chemical element, symbol Tb and atomic number 65

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<span class="mw-page-title-main">Thulium</span> Chemical element, symbol Tm and atomic number 69

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<span class="mw-page-title-main">Zirconium</span> Chemical element, symbol Zr and atomic number 40

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<span class="mw-page-title-main">Alkaline earth metal</span> Group of chemical elements

The alkaline earth metals are six chemical elements in group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). The elements have very similar properties: they are all shiny, silvery-white, somewhat reactive metals at standard temperature and pressure.

A period 5 element is one of the chemical elements in the fifth row of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The fifth period contains 18 elements, beginning with rubidium and ending with xenon. As a rule, period 5 elements fill their 5s shells first, then their 4d, and 5p shells, in that order; however, there are exceptions, such as rhodium.

<span class="mw-page-title-main">Praseodymium</span> Chemical element, symbol Pr and atomic number 59

Praseodymium is a chemical element; it has symbol Pr and the atomic number 59. It is the third member of the lanthanide series and is considered one of the rare-earth metals. It is a soft, silvery, malleable and ductile metal, valued for its magnetic, electrical, chemical, and optical properties. It is too reactive to be found in native form, and pure praseodymium metal slowly develops a green oxide coating when exposed to air.

<span class="mw-page-title-main">Group 3 element</span> Group of chemical elements

Group 3 is the first group of transition metals in the periodic table. This group is closely related to the rare-earth elements. It contains the four elements scandium (Sc), yttrium (Y), lutetium (Lu), and lawrencium (Lr). The group is also called the scandium group or scandium family after its lightest member.

<span class="mw-page-title-main">Yttrium</span> Chemical element, symbol Y and atomic number 39

Yttrium is a chemical element; it has symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a "rare-earth element". Yttrium is almost always found in combination with lanthanide elements in rare-earth minerals and is never found in nature as a free element. 89Y is the only stable isotope and the only isotope found in the Earth's crust.

<span class="mw-page-title-main">Cerium</span> Chemical element, symbol Ce and atomic number 58

Cerium is a chemical element; it has symbol Ce and atomic number 58. Cerium is a soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it often shows the oxidation state of +3 characteristic of the series, it also has a stable +4 state that does not oxidize water. It is also considered one of the rare-earth elements. Cerium has no known biological role in humans but is not particularly toxic, except with intense or continued exposure.

Scandium compounds are compounds containing the element scandium. The chemistry of scandium is almost completely dominated by the trivalent ion, Sc3+, due to its electron configuration, [Ar] 3d14s2. The radii of M3+ ions in the table below indicate that the chemical properties of scandium ions have more in common with yttrium ions than with aluminium ions. In part because of this similarity, scandium is often classified as a lanthanide-like element.

An yttrium compound is a chemical compound containing yttrium. Among these compounds, yttrium generally has a +3 valence. The solubility properties of yttrium compounds are similar to those of the lanthanides. For example oxalates and carbonates are hardly soluble in water, but soluble in excess oxalate or carbonate solutions as complexes are formed. Sulfates and double sulfates are generally soluble. They resemble the "yttrium group" of heavy lanthanide elements.


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