Europium is a lanthanide with the symbol Eu and atomic number 63. It is a steel-gray metal about as reactive as calcium. Although difficult to find and rather expensive, it and its salts have very interesting properties that make it an excellent addition to the amateur chemist's lab. Among these properties are multi-colored fluorescence, redox chemistry and paramagnetism, brought about by the element's half-filled f-shell. Europium can exist in a +2 state in a reducing environment, which can be an excellent exercise in preparing reduced compounds, as the reaction Eu2+ → Eu3+ + e- is even less favored than Cr2+ → Cr3+ + e-, which is a standard exercise in the lab.
Europium is by far the most reactive lanthanide, quickly corroding in air. The highly favorable reaction Eu → Eu2+ + e- and the increased stability of europium(II) accelerates the corrosion rate of the metal such that a small piece exposed to dry air will corrode within a month. The resulting yellow powder, nearly the color of mustard, slowly fades as it turns from europium(II) to europium(III), the most stable form of europium. A mixed oxide of europium(II) and europium(III) has been reported, as have europium(II) sulfide, europium(II) chloride, and europium(II) sulfate, which is very similar to calcium and barium sulfate and highly insoluble.
Europium metal burns in air with a bright red flame, identical to that of samarium, and forms the oxide in air. When europium contacts water, it will react with water about as quickly as calcium metal, and will form the yellow divalent hydroxide, which slowly converts to the trivalent hydroxide.
Freshly cut europium is grayish, but quickly develops a thick layer of yellow and graphite-colored oxides. It is a relatively soft metal, and is relatively soft. Europium(II) compounds exhibit a blue fluorescence, and europium(III) compounds exhibit a red fluorescence. The fluorescence may be enhanced by the complexation of dipicolinate or other planar ligands to a europium atom.
Europium is more common than iodine on Earth, but it is hard to find and extremely expensive. Places like Sigma-Aldrich charge $1000 for five measly grams. One source for europium, as well as other rare earth metals, is Metallium. It is sold in 5 gram (thankfully only $50) and 25 gram sizes, as well as rods, ampoules, and coins. Metallium also takes custom orders. Europium and its compounds may be occasionally found on eBay. Other places such as NewMet will sell europium rods, sheets, foils at any size and no minimum order, though the price is on request.
- Preparing reduced europium compounds
- Producing fluorescent crystals (blue and red)
- Producing triboluminescent europium tetrakis(dibenzoylmethide)triethylammonium
Safety and storageEdit
Europium metal, especially as a dust, should always be kept away from water and open flames. Europium fires can be identified by their bright red flames. Never use water to put out europium fire, as this will aggravate it. Class D fire extinguishers are recommended for this type of fire.
Europium requires storage under an inert atmosphere or mineral oil to prevent corrosion. When exposed to air, europium corrodes very easily, and it is not possible to reduce europium compounds to europium metal without an aprotic solvent.