Scandium (IPA: /?skandi?m/) is a chemical element in the periodic table that has the symbol Sc and atomic number 21. A soft, silvery, white metal, scandium ore occurs in rare minerals from Scandinavia and elsewhere, and it is sometimes considered along with yttrium, and the lanthanides and actinides, to be a rare earth.
Scandium is a rare, soft, silvery, very light metallic element that develops a slightly yellowish or pinkish cast when exposed to air. 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. In this area of atomic numbers, the thermonuclear reactions that produced the elements, very much more commonly produces elements with an even atomic number. This is because 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 number 18 argon, number 20 calcium, number 22 titanium, number 24 chromium; with the odd-numbered elements 19 potassium, 21 scandium, and 23 vanadium being rarely produced, and much less common. The production of the odd-numbered elements in this range results from much-less common thermonuclear reactions, as is explained elsewhere.
Since it is a very rare metal, scandium doesn't have many applications. If it were more common, it might be useful in the making of aircraft and spacecraft structures, probably alloyed with other metals. Approximately 20 kg (as Sc2O3) of scandium is used annually in the United States to make high-intensity lights.  Scandium iodide added to mercury-vapor lamps produces an efficient artificial light source that resembles sunlight, and which allows good color-reproduction with TV cameras. About 80 kg of scandium is used in light bulbs globally per year. The radioactive isotope Sc-46 is used in oil refinerys as a tracing agent. 
The main application of scandium by weight is in aluminium-scandium alloys for minor aerospace industry components, and for unusual designs sports equipment (bikes, baseball bats, firearms, etc.) which rely on high performance materials. However, titanium, being much more common, and similar in lightness and strength, is much more widely used, with tons found in some aircraft, especially military ones.
When added to aluminium, scandium substantially lowers the rate of recrystallization and associated grain-growth in weld heat-affected zones. Aluminium, being a face-centred-cubic metal, is not particularly subject to the strengthening effects of the a decrease in grain diameter. However, the presence of fine dispersions of Al3Sc does increase strength by a small measure, much as any other precipitate system in aluminium alloys. It is added to aluminum alloys primarily to control that otherwise excessive grain growth in the heat-affected zone of weldable structural aluminium alloys, which gives two knock-on effects; greater strengthening via finer precipitation of other alloying elements and by reducing the precipitate-free zones that normally surround exist at the grain boundaries of age-hardening aluminium alloys.
The original use of scandium-aluminium alloys was in the nose cones of some USSR submarine-launched ballistic missiles (SLBMs). The strength of the resulting nose cone was enough to enable it to pierce the ice-cap without damage, and so, enabling a missile launch, while still submerged under the Arctic ice cap.
Dmitri Mendeleev used his periodic law, in 1869, to predict the existence of, and some properties of, three unknown elements, including one he called ekaboron .
Lars Fredrick Nilson and his team, apparently unaware of that prediction in the spring of 1879, were looking for rare earth metals. By using spectral analysis, they found a new element within the minerals euxenite and gadolinite. They named it scandium, from the Latin Scandia meaning "Scandinavia", and in the process of isolating the scandium, they processed 10 kilograms of euxenite, producing about 2.0 grams of a very pure scandium oxide (Sc2O3).
Per Teodor Cleve of Sweden concluded that scandium corresponded well to the hoped-for ekaboron, and he notified Mendeleev of this in August.
Fischer, Brunger, and Grienelaus prepared metallic scandium for the first time in 1937, by electrolysis of a eutectic melt of potassium, lithium, and scandium chlorides at a temperture of 700 to 800°C. Tungsten wires in a pool of liquid zinc were the electrodes in a graphite crucible. The first pound of 99% pure scandium metal was not produced until 1960.