Europium

Europium,  ₆₃Eu

General properties
Name, symbol	Europium, Eu
Appearance	Silvery white
Europium in the periodic table
- ↑ Eu ↓ Am Samarium ← Europium → Gadolinium
Atomic number	63
Standard atomic weight (Ar)	151.964(1)
Group, block	, f-block
Period	period 6
Electron configuration	[Xe] 4f7 6s2
per shell	2, 8, 18, 25, 8, 2
Physical properties
Silvery-white
Phase	Solid
Melting point	1099 K ​(826 °C, ​​1519 °F)
Boiling point	1802 K ​(1529 °C, ​​2784 °F)
Density near r.t.	5.264 g/cm3
when liquid, at	5.13 g/cm3
Heat of fusion	9.21 kJ/mol
Heat of	176 kJ/mol
Molar heat capacity	27.66 J/(mol·K)
pressure
Atomic properties
Oxidation states	3, 2, 1 ​(a mildly basic oxide)
Electronegativity	Pauling scale: 1.2
energies	1st: 547.1 kJ/mol 2nd: 1085 kJ/mol 3rd: 2404 kJ/mol
Atomic radius	empirical: 180 pm
Covalent radius	198±6 pm
Miscellanea
Crystal structure	​Body-centered cubic (bcc)
Thermal expansion	35.0 µm/(m·K) (poly)
Thermal conductivity	13.9 W/(m·K)
Electrical resistivity	9·10-7 Ω·m (poly)
Magnetic ordering	Paramagnetic
Young's modulus	18.2 GPa
Shear modulus	7.9 GPa
Bulk modulus	8.3 GPa
Poisson ratio	0.152
Vickers hardness	165–200 MPa
CAS Registry Number	7440-53-1
History
Naming	After Europe
Discovery and first isolation	Eugène-Anatole Demarçay (1896, 1901)

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.

Properties

Physical

Freshly cut europium is grayish, but quickly develops a thick layer of yellow and graphite-colored oxides. It is a relatively soft metal, softer than other lanthanides, and can be cut with a cutting tool. Europium(II) compounds exhibit a blue fluorescence (though this varies significantly with the coordinating ligands), 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.

Chemical

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 in that it is highly insoluble in water.

Europium metal burns in air with a bright red flame, identical to that of samarium to form the oxide. When europium contacts water, it will react with water about as quickly as calcium, and will form the yellow divalent hydroxide, which converts to the trivalent hydroxide on further exposure to water. When dry, it absorbs carbon dioxide from the air to make europium(III) carbonate.

Availability

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.

Projects

• Preparing reduced europium compounds
• Producing fluorescent crystals (blue and red)
• Producing triboluminescent europium tetrakis(dibenzoylmethide)triethylammonium
• Element collecting

Safety

Safety

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.

Storage

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.

Disposal

Since europium expensive and rare, it's best to try to recycle it.

References

Relevant Sciencemadness threads

• Production and storage of europium(II) compounds