Europium (Eu)

• Element Symbol: Eu
• Atomic Number: 63
• Atomic Mass: 151.964
• Group # in Periodic Table: n/a
• Group Name: Lanthanides
• Period in Periodic Table: 6
• Block of Periodic Table: f-block
• Discovered by: Eugène-Anatole Demarçay (1896)

Europium is a soft, silvery-gray metal. It is part of the lanthanide series, which includes elements with atomic numbers from 57 to 71 in the periodic table. Like the other elements in this series, europium is a rare earth element. It can be found with other rare earth elements in certain minerals within Earth’s crust. Minerals that may contain europium include bastnaesite, loparite, monazite, and xenotime. Europium metal is not found in its pure form in nature.

A variety of lanthanides are often found within the same minerals. The development of techniques for isolating these elements from those minerals led to the discovery of europium. In the 1800s chemists studying rare earth elements found lanthanum, praseodymium, neodymium, and samarium in samples that had initially been thought to contain only cerium. The samarium sample was examined further and found to contain gadolinium. Even more chemical processing of samarium by French chemist Eugène-Anatole Demarçay led to the discovery of europium in 1901. This element is named for the continent of Europe.

Physical Properties

Europium is silvery gray and solid in its standard state—that is, its state at 298 kelvins (K). It is the softest lanthanide and a highly ductile metal. Europium has a density of 5.244 grams per cubic centimeter (g/cm³) at standard state, which makes it the least dense of the lanthanides. Its melting point is 822 degrees Celsius (ºC). Its boiling point is 1527 ºC. The specific heat of europium is 182 joules per kilogram-kelvin (J/kg·K). Europium is a good conductor of both heat and electricity. Its thermal conductivity is 14 watts per meter-kelvin (W/m·K), and its electrical conductivity is 1.1 × 10⁶ siemens per meter (S/m). Its resistivity is 9 × 10⁻⁷ meter-ohms (m·Ω). Europium becomes a superconductor at extremely low temperatures (below 1.8 K) and high pressure (above 80 gigapascals). Europium is strongly paramagnetic at most temperatures, which means it has only a small response to a magnetic field.

Chemical Properties

Europium has a body-centered cubic crystal structure. A variety of europium compounds produce red phosphors. Europium also fluoresces in the presence of ultraviolet light. Europium is highly reactive with air, oxidizing to form a gray surface layer. Shavings and dust of europium ignite and burn at temperatures in the 150–180 ºC range. Europium also reacts with water and dissolves in most dilute acids. When dissolved in dilute sulfuric acid, europium forms a light pink solution. Like other lanthanides, europium does not dissolve in hydrofluoric acid. It instead forms a protective europium trifluoride layer on the acid’s surface.

The electron affinity of europium is 50 kilojoules per mole (kJ/mol). Europium has three valence electrons. Its ionization energies are 547.1, 1085, 2404, and 4120 kJ/mol. It has two oxidation states: +3 and +2. This is different from the oxidation states of most other lanthanides, which have only the +3 oxidation state. Light pink salts are produced in its +3 oxidation state. Salts that range from white to yellow or green are produced in its +2 oxidation state.

Europium has two naturally occurring isotopes. The most common of them is europium-153, a stable isotope that represents around 52 percent of the europium on Earth. The other is europium-151, which represents the remaining 48 percent of europium. This isotope was previously thought to be stable. However, studies have shown that it decays very slowly. Its half-life is greater than 1.7 × 10¹⁸ years. Thirty-four other radioactive isotopes of europium have been produced during nuclear fission. Their half-lives range from 0.9 milliseconds to 36.9 years. This element has an electron configuration of [Xe]4f⁷6s².

Applications

Europium is a very rare lanthanide. It is similar to bromine in its abundance. Only 0.00018 percent of Earth’s crust is estimated to consist of europium. Because of its scarcity, only around 91 tons of europium are produced each year. Countries that produce this element include China and the United States.

Europium can sometimes be found in a much larger or much smaller concentration than expected within minerals bearing rare earth elements. This difference in relative concentration is called the "europium anomaly." An accumulation of europium often exists in rock formed from magma rich in plagioclase minerals. Rock formed from magma that does not contain much plagioclase contains depleted stores of europium. Moon rocks brought back from the lunar surface during the Apollo missions demonstrate the europium anomaly. Rocks from the moon’s highlands are rich in a plagioclase mineral and have a positive europium anomaly. Rocks from the moon’s maria (basaltic plains) are not rich in plagioclase and have a negative europium anomaly.

Solvent extraction and ion exchange are used to separate lanthanides from their minerals. Pure europium metal is then obtained by heating europium(III) oxide with lanthanum in a tantalum crucible.

Before the invention of LED and plasma screens, europium was instrumental in producing the vivid reds seen in cathode-ray television sets. Phosphors containing europium emitted bright red light. Before europium was used, reds in televisions were dull compared to blues and greens.

Europium’s ability to emit red light makes it useful in compact fluorescent light bulbs. Without europium, these bulbs emit light with a greenish cast. With europium added, the light emitted has a wider spectrum and more closely resembles sunlight.

Europium is added to some of the phosphorescent powders used in glow-in-the-dark paint. Strontium aluminate that contains europium causes green and aqua paint to glow.

Like many other lanthanides, europium has the ability to absorb neutrons. Because of this property, europium can be used in the rods within nuclear reactors.

Europium has been added to the paper euro notes used as money within the European Union. The europium in these notes glows red when the note is exposed to ultraviolet light. This property can be used to distinguish a real euro note from a counterfeit note.

Bibliography

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"Europium." Periodic Table. Royal Soc. of Chemistry, 2015. Web. 11 Sept. 2015.

"Europium (Eu)." Encyclopædia Britannica. Encyclopædia Britannica, 12 Nov. 2013. Web. 11 Sept. 2015.

Gray, Theodore. The Elements: A Visual Exploration of Every Known Atom in the Universe. New York: Black Dog, 2009. Print.

Parsons, Paul, and Gail Dixon. The Periodic Table: A Visual Guide to the Elements. New York: Quercus, 2014. Print.

"Technical Data for Europium." The Photographic Periodic Table of the Elements. Element Collection, n.d. Web. 11 Sept. 2015.