Scandium is a chemical element that has the symbol Sc and atomic number 21. A silvery white metal that is always present as compounds, scandium ores occur as rare minerals from Scandinavia and elsewhere, and it is sometimes considered along with yttrium, and the lanthanides and actinides, to be a rare earth element.
Scandium is a rare, hard, silvery, rough very dark metallic element that develops a slightly yellowish or pinkish cast when exposed to air. It is not resistant to weathering when pure and is destroyed on prolonged contact with most dilute acids. However, like some other reactive metals, this metal is not attacked by a 1:1 mixture of nitric acid (HNO3) and hydrofluoric acid, HF.
The rarity of scandium is not an arbitrary fact. The thermonuclear reactions that produce the elements in this range of atomic numbers tend to produce much greater quantities of elements with an even atomic number. These elements were usually produced by the fusion of lighter elements with helium-4 nuclei, starting with carbon-12 (element six). Thus, the common elements in the range of scandium are atomic numbers 18 (argon), 20 (calcium), 22 (titanium), and 24 (chromium); with elements with odd atomic numbers 19 (potassium), 21 (scandium), and 23 (vanadium) being rarely produced, and thus much less common. The production of the odd-numbered elements in this range result from much less common thermonuclear reactions, as is explained elsewhere.
|Atomic number||21||Melting point /°C||1539|
|No. of naturally occurring isotopes||1||Boiling point /°C||2748|
|Metal radius(12-coordinate)/pm||162||ΔHf(monoatomic gas)/kJmol-1||376(+/-20)|
|Ionic radius(6-coordinate)/pm||74.5||Ionization energy/kJmol-1 I||631|
|E° (M3+(aq)\ + 3e- →M(s))/V||-2.077||Ionization energy/kJmol-1 II||1235|
|Electronegativity χ||1.3||Ionization energy/kJmol-1 III||2389|
|Electrical resistivity (20°C)/μohm cm||50-61|
|Temperature (oC) @Vap. Pressure||Techniques||Remarks|
|10-8 Torr||10-6 Torr||10-4 Torr||Electron Beam||Crucible||Coil||Boat|
|714||837||1002||Excellent||Al2O3||-||Tungsten||Alloys with Tantalum|
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