|Pronunciation|| / /|
|Appearance||silvery white, with a pale yellow tint; but rarely seen without oxide discoloration|
|Standard atomic weight Ar, std(Eu)||151.964(1)|
|Europium in the periodic table|
|Atomic number (Z)||63|
|Electron configuration||[ Xe ] 4f7 6s2|
|Electrons per shell||2, 8, 18, 25, 8, 2|
|Phase at STP||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 m.p.)||5.13 g/cm3|
|Heat of fusion||9.21 kJ/mol|
|Heat of vaporization||176 kJ/mol|
|Molar heat capacity||27.66 J/(mol·K)|
| Vapor pressure |
|Oxidation states||+1, +2, +3 (a mildly basic oxide)|
|Electronegativity||Pauling scale: 1.2|
|Atomic radius||empirical:180 pm|
|Covalent radius||198±6 pm|
|Spectral lines of europium|
|Crystal structure|| body-centered cubic (bcc)|
|Thermal expansion||poly: 35.0 µm/(m·K)(at r.t.)|
|Thermal conductivity||est. 13.9 W/(m·K)|
|Electrical resistivity||poly: 0.900 µΩ·m(at r.t.)|
|Magnetic susceptibility||+34,000.0·10−6 cm3/mol|
|Young's modulus||18.2 GPa|
|Shear modulus||7.9 GPa|
|Bulk modulus||8.3 GPa|
|Vickers hardness||165–200 MPa|
|Discovery and first isolation||Eugène-Anatole Demarçay (1896,1901)|
|Main isotopes of europium|
Europium is a chemical element with the symbol Eu and atomic number 63. Europium is the most reactive lanthanide by far, having to be stored under an inert fluid to protect it from atmospheric oxygen or moisture. Europium is also the softest lanthanide, as it can be dented with a finger nail and easily cut with a knife. When oxidation is removed a shiny-white metal is visible. Europium was isolated in 1901 and is named after the continent of Europe.Being a typical member of the lanthanide series, europium usually assumes the oxidation state +3, but the oxidation state +2 is also common. All europium compounds with oxidation state +2 are slightly reducing. Europium has no significant biological role and is relatively non-toxic compared to other heavy metals. Most applications of europium exploit the phosphorescence of europium compounds. Europium is one of the rarest of the rare earth elements on Earth.
Europium is a ductile metal with a hardness similar to that of lead. It crystallizes in a body-centered cubic lattice.Some properties of europium are strongly influenced by its half-filled electron shell. Europium has the second lowest melting point and the lowest density of all lanthanides.
Europium becomes a superconductor when it is cooled below 1.8 K and compressed to above 80 GPa. This occurs because europium is divalent in the metallic state,and is converted into the trivalent state by the applied pressure. In the divalent state, the strong local magnetic moment (J = 7/2) suppresses the superconductivity, which is induced by eliminating this local moment (J = 0 in Eu3+).
Europium is the most reactive rare-earth element. It rapidly oxidizes in air, so that bulk oxidation of a centimeter-sized sample occurs within several days.Its reactivity with water is comparable to that of calcium, and the reaction is
Because of the high reactivity, samples of solid europium rarely have the shiny appearance of the fresh metal, even when coated with a protective layer of mineral oil. Europium ignites in air at 150 to 180 °C to form europium(III) oxide:
Europium dissolves readily in dilute sulfuric acid to form pale pink solutions of the hydrated Eu(III), which exist as a nonahydrate:
Although usually trivalent, europium readily forms divalent compounds. This behavior is unusual for most lanthanides, which almost exclusively form compounds with an oxidation state of +3. The +2 state has an electron configuration 4f7 because the half-filled f-shell provides more stability. In terms of size and coordination number, europium(II) and barium(II) are similar. The sulfates of both barium and europium(II) are also highly insoluble in water.Divalent europium is a mild reducing agent, oxidizing in air to form Eu(III) compounds. In anaerobic, and particularly geothermal conditions, the divalent form is sufficiently stable that it tends to be incorporated into minerals of calcium and the other alkaline earths. This ion-exchange process is the basis of the "negative europium anomaly", the low europium content in many lanthanide minerals such as monazite, relative to the chondritic abundance. Bastnäsite tends to show less of a negative europium anomaly than does monazite, and hence is the major source of europium today. The development of easy methods to separate divalent europium from the other (trivalent) lanthanides made europium accessible even when present in low concentration, as it usually is.
Naturally occurring europium is composed of 2 isotopes, 151Eu and 153Eu, which occur in almost equal proportions; 153Eu is slightly more abundant (52.2% natural abundance). While 153Eu is stable, 151Eu was found to be unstable to alpha decay with a half-life of 5+11
−3×1018 years in 2007, giving about 1 alpha decay per two minutes in every kilogram of natural europium. This value is in reasonable agreement with theoretical predictions. Besides the natural radioisotope 151Eu, 35 artificial radioisotopes have been characterized, the most stable being 150Eu with a half-life of 36.9 years, 152Eu with a half-life of 13.516 years, and 154Eu with a half-life of 8.593 years. All the remaining radioactive isotopes have half-lives shorter than 4.7612 years, and the majority of these have half-lives shorter than 12.2 seconds. This element also has 8 meta states, with the most stable being 150mEu (t1/2=12.8 hours), 152m1Eu (t1/2=9.3116 hours) and 152m2Eu (t1/2=96 minutes).
The primary decay mode for isotopes lighter than 153Eu is electron capture, and the primary mode for heavier isotopes is beta minus decay. The primary decay products before 153Eu are isotopes of samarium (Sm) and the primary products after are isotopes of gadolinium (Gd).
| t½ |
| Yield |
| Q |
Europium is produced by nuclear fission, but the fission product yields of europium isotopes are low near the top of the mass range for fission products.
As with other lanthanides, many isotopes of europium, especially those that have odd mass numbers or are neutron-poor like 152Eu, have high cross sections for neutron capture, often high enough to be neutron poisons.
151Eu is the beta decay product of samarium-151, but since this has a long decay half-life and short mean time to neutron absorption, most 151Sm instead ends up as 152Sm.
152Eu (half-life 13.516 years) and 154Eu (half-life 8.593 years) cannot be beta decay products because 152Sm and 154Sm are non-radioactive, but 154Eu is the only long-lived "shielded" nuclide, other than 134Cs, to have a fission yield of more than 2.5 parts per million fissions.A larger amount of 154Eu is produced by neutron activation of a significant portion of the non-radioactive 153Eu; however, much of this is further converted to 155Eu.
155Eu (half-life 4.7612 years) has a fission yield of 330 parts per million (ppm) for uranium-235 and thermal neutrons; most of it is transmuted to non-radioactive and nonabsorptive gadolinium-156 by the end of fuel burnup.
Overall, europium is overshadowed by caesium-137 and strontium-90 as a radiation hazard, and by samarium and others as a neutron poison.
Europium is not found in nature as a free element. Many minerals contain europium, with the most important sources being bastnäsite, monazite, xenotime and loparite-(Ce).No europium-dominant minerals are known yet, despite a single find of a tiny possible Eu–O or Eu–O–C system phase in the Moon's regolith.
Depletion or enrichment of europium in minerals relative to other rare-earth elements is known as the europium anomaly.Europium is commonly included in trace element studies in geochemistry and petrology to understand the processes that form igneous rocks (rocks that cooled from magma or lava). The nature of the europium anomaly found helps reconstruct the relationships within a suite of igneous rocks. The average crustal abundance of europium is 2-2.2 ppm.
Divalent europium (Eu2+) in small amounts is the activator of the bright blue fluorescence of some samples of the mineral fluorite (CaF2). The reduction from Eu3+ to Eu2+ is induced by irradiation with energetic particles.The most outstanding examples of this originated around Weardale and adjacent parts of northern England; it was the fluorite found here that fluorescence was named after in 1852, although it was not until much later that europium was determined to be the cause.
In astrophysics, the signature of europium in stellar spectra can be used to classify stars and inform theories of how or where a particular star was born. For instance, astronomers recently identified higher-than-expected levels of europium within the star J1124+4535, hypothesizing that this star originated in a dwarf galaxy that collided with the Milky Way billions of years ago.
Europium is associated with the other rare-earth elements and is, therefore, mined together with them. Separation of the rare-earth elements occurs during later processing. Rare-earth elements are found in the minerals bastnäsite, loparite-(Ce), xenotime, and monazite in mineable quantities. Bastnäsite is a group of related fluorocarbonates, Ln(CO3)(F,OH). Monazite is a group of related of orthophosphate minerals LnPO
4 (Ln denotes a mixture of all the lanthanides except promethium), loparite-(Ce) is an oxide, and xenotime is an orthophosphate (Y,Yb,Er,...)PO4. Monazite also contains thorium and yttrium, which complicates handling because thorium and its decay products are radioactive. For the extraction from the ore and the isolation of individual lanthanides, several methods have been developed. The choice of method is based on the concentration and composition of the ore and on the distribution of the individual lanthanides in the resulting concentrate. Roasting the ore, followed by acidic and basic leaching, is used mostly to produce a concentrate of lanthanides. If cerium is the dominant lanthanide, then it is converted from cerium(III) to cerium(IV) and then precipitated. Further separation by solvent extractions or ion exchange chromatography yields a fraction which is enriched in europium. This fraction is reduced with zinc, zinc/amalgam, electrolysis or other methods converting the europium(III) to europium(II). Europium(II) reacts in a way similar to that of alkaline earth metals and therefore it can be precipitated as a carbonate or co-precipitated with barium sulfate. Europium metal is available through the electrolysis of a mixture of molten EuCl3 and NaCl (or CaCl2) in a graphite cell, which serves as cathode, using graphite as anode. The other product is chlorine gas.
A few large deposits produce or produced a significant amount of the world production. The Bayan Obo iron ore deposit contains significant amounts of bastnäsite and monazite and is, with an estimated 36 million tonnes of rare-earth element oxides, the largest known deposit.The mining operations at the Bayan Obo deposit made China the largest supplier of rare-earth elements in the 1990s. Only 0.2% of the rare-earth element content is europium. The second large source for rare-earth elements between 1965 and its closure in the late 1990s was the Mountain Pass rare earth mine. The bastnäsite mined there is especially rich in the light rare-earth elements (La-Gd, Sc, and Y) and contains only 0.1% of europium. Another large source for rare-earth elements is the loparite found on the Kola peninsula. It contains besides niobium, tantalum and titanium up to 30% rare-earth elements and is the largest source for these elements in Russia.
Europium compounds tend to exist trivalent oxidation state under most conditions. Commonly these compounds feature Eu(III) bound by 6–9 oxygenic ligands, typically water. These compounds, the chlorides, sulfates, nitrates, are soluble in water or polar organic solvent. Lipophilic europium complexes often feature acetylacetonate-like ligands, e.g., Eufod.
Europium metal reacts with all the halogens:
This route gives white europium(III) fluoride (EuF3), yellow europium(III) chloride (EuCl3), gray europium(III) bromide (EuBr3), and colorless europium(III) iodide (EuI3). Europium also forms the corresponding dihalides: yellow-green europium(II) fluoride (EuF2), colorless europium(II) chloride (EuCl2), colorless europium(II) bromide (EuBr2), and green europium(II) iodide (EuI2).
Europium forms stable compounds with all of the chalcogens, but the heavier chalcogens (S, Se, and Te) stabilize the lower oxidation state. Three oxides are known: europium(II) oxide (EuO), europium(III) oxide (Eu2O3), and the mixed-valence oxide Eu3O4, consisting of both Eu(II) and Eu(III). Otherwise, the main chalcogenides are europium(II) sulfide (EuS), europium(II) selenide (EuSe) and europium(II) telluride (EuTe): all three of these are black solids. EuS is prepared by sulfiding the oxide at temperatures sufficiently high to decompose the Eu2O3:
The main nitride is europium(III) nitride (EuN).
Although europium is present in most of the minerals containing the other rare elements, due to the difficulties in separating the elements it was not until the late 1800s that the element was isolated. William Crookes observed the phosphorescent spectra of the rare elements including those eventually assigned to europium.
Europium was first found in 1892 by Paul Émile Lecoq de Boisbaudran, who obtained basic fractions from samarium-gadolinium concentrates which had spectral lines not accounted for by samarium or gadolinium. However, the discovery of europium is generally credited to French chemist Eugène-Anatole Demarçay, who suspected samples of the recently discovered element samarium were contaminated with an unknown element in 1896 and who was able to isolate it in 1901; he then named it europium.
When the europium-doped yttrium orthovanadate red phosphor was discovered in the early 1960s, and understood to be about to cause a revolution in the color television industry, there was a scramble for the limited supply of europium on hand among the monazite processors,as the typical europium content in monazite is about 0.05%. However, the Molycorp bastnäsite deposit at the Mountain Pass rare earth mine, California, whose lanthanides had an unusually high europium content of 0.1%, was about to come on-line and provide sufficient europium to sustain the industry. Prior to europium, the color-TV red phosphor was very weak, and the other phosphor colors had to be muted, to maintain color balance. With the brilliant red europium phosphor, it was no longer necessary to mute the other colors, and a much brighter color TV picture was the result. Europium has continued to be in use in the TV industry ever since as well as in computer monitors. Californian bastnäsite now faces stiff competition from Bayan Obo, China, with an even "richer" europium content of 0.2%.
Frank Spedding, celebrated for his development of the ion-exchange technology that revolutionized the rare-earth industry in the mid-1950s, once related the story of howhe was lecturing on the rare earths in the 1930s, when an elderly gentleman approached him with an offer of a gift of several pounds of europium oxide. This was an unheard-of quantity at the time, and Spedding did not take the man seriously. However, a package duly arrived in the mail, containing several pounds of genuine europium oxide. The elderly gentleman had turned out to be Herbert Newby McCoy, who had developed a famous method of europium purification involving redox chemistry.
Relative to most other elements, commercial applications for europium are few and rather specialized. Almost invariably, its phosphorescence is exploited, either in the +2 or +3 oxidation state.
It is a dopant in some types of glass in lasers and other optoelectronic devices. Europium oxide (Eu2O3) is widely used as a red phosphor in television sets and fluorescent lamps, and as an activator for yttrium-based phosphors. g of europium oxide. Whereas trivalent europium gives red phosphors, the luminescence of divalent europium depends strongly on the composition of the host structure. UV to deep red luminescence can be achieved. The two classes of europium-based phosphor (red and blue), combined with the yellow/green terbium phosphors give "white" light, the color temperature of which can be varied by altering the proportion or specific composition of the individual phosphors. This phosphor system is typically encountered in helical fluorescent light bulbs. Combining the same three classes is one way to make trichromatic systems in TV and computer screens, but as an additive, it can be particularly effective in improving the intensity of red phosphor. Europium is also used in the manufacture of fluorescent glass, increasing the general efficiency of fluorescent lamps. One of the more common persistent after-glow phosphors besides copper-doped zinc sulfide is europium-doped strontium aluminate. Europium fluorescence is used to interrogate biomolecular interactions in drug-discovery screens. It is also used in the anti-counterfeiting phosphors in euro banknotes.Color TV screens contain between 0.5 and 1
An application that has almost fallen out of use with the introduction of affordable superconducting magnets is the use of europium complexes, such as Eu(fod)3, as shift reagents in NMR spectroscopy. Chiral shift reagents, such as Eu(hfc)3, are still used to determine enantiomeric purity.
A recent (2015) application of europium is in quantum memory chips which can reliably store information for days at a time; these could allow sensitive quantum data to be stored to a hard disk-like device and shipped around.
|GHS Signal word||Danger|
|P222, P231, P422|
|NFPA 704 (fire diamond)|
There are no clear indications that europium is particularly toxic compared to other heavy metals. Europium chloride, nitrate and oxide have been tested for toxicity: europium chloride shows an acute intraperitoneal LD50 toxicity of 550 mg/kg and the acute oral LD50 toxicity is 5000 mg/kg. Europium nitrate shows a slightly higher intraperitoneal LD50 toxicity of 320 mg/kg, while the oral toxicity is above 5000 mg/kg. The metal dust presents a fire and explosion hazard.
The actinide or actinoid series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.
Gadolinium is a chemical element with the symbol Gd and atomic number 64. Gadolinium is a silvery-white metal when oxidation is removed. It is only slightly malleable and is a ductile rare-earth element. Gadolinium reacts with atmospheric oxygen or moisture slowly to form a black coating. Gadolinium below its Curie point of 20 °C (68 °F) is ferromagnetic, with an attraction to a magnetic field higher than that of nickel. Above this temperature it is the most paramagnetic element. It is found in nature only in an oxidized form. When separated, it usually has impurities of the other rare-earths because of their similar chemical properties.
Holmium is a chemical element with the symbol Ho and atomic number 67. Part of the lanthanide series, holmium is a rare-earth element. Holmium was discovered by Swedish chemist Per Theodor Cleve. Its oxide was first isolated from rare-earth ores in 1878. The element's name comes from Holmia, the Latin name for the city of Stockholm.
Lanthanum is a chemical element with the symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air and is soft enough to be cut with a knife. It is the eponym of the lanthanide series, a group of 15 similar elements between lanthanum and lutetium in the periodic table, of which lanthanum is the first and the prototype. It is also sometimes considered the first element of the 6th-period transition metals, which would put it in group 3, although lutetium is sometimes placed in this position instead. Lanthanum is traditionally counted among the rare earth elements. The usual oxidation state is +3. Lanthanum has no biological role in humans but is essential to some bacteria. It is not particularly toxic to humans but does show some antimicrobial activity.
Lutetium is a chemical element with the symbol Lu and atomic number 71. It is a silvery white metal, which resists corrosion in dry air, but not in moist air. Lutetium is the last element in the lanthanide series, and it is traditionally counted among the rare earths. Lutetium is sometimes considered the first element of the 6th-period transition metals, although lanthanum is more often considered as such.
The lanthanide or lanthanoid series of chemical elements comprises the 15 metallic chemical elements with atomic numbers 57–71, from lanthanum through lutetium. These elements, along with the chemically similar elements scandium and yttrium, are often collectively known as the rare earth elements.
Neodymium is a chemical element with the symbol Nd and atomic number 60. Neodymium belongs to the lanthanide series and is a rare-earth element. It is a hard, slightly malleable silvery metal that quickly tarnishes in air and moisture. When oxidized, neodymium reacts quickly to produce pink, purple/blue and yellow compounds in the +2, +3 and +4 oxidation states. Neodymium was discovered in 1885 by the Austrian chemist Carl Auer von Welsbach. It is present in significant quantities in the ore minerals monazite and bastnäsite. Neodymium is not found naturally in metallic form or unmixed with other lanthanides, and it is usually refined for general use. Although neodymium is classed as a rare-earth element, it is fairly common, no rarer than cobalt, nickel, or copper, and is widely distributed in the Earth's crust. Most of the world's commercial neodymium is mined in China.
Promethium is a chemical element with the symbol Pm and atomic number 61. All of its isotopes are radioactive; it is extremely rare, with only about 500–600 grams naturally occurring in Earth's crust at any given time. Promethium is one of only two radioactive elements that are followed in the periodic table by elements with stable forms, the other being technetium. Chemically, promethium is a lanthanide. Promethium shows only one stable oxidation state of +3.
Samarium is a chemical element with the symbol Sm and atomic number 62. It is a moderately hard silvery metal that slowly oxidizes in air. Being a typical member of the lanthanide series, samarium usually assumes the oxidation state +3. Compounds of samarium(II) are also known, most notably the monoxide SmO, monochalcogenides SmS, SmSe and SmTe, as well as samarium(II) iodide. The last compound is a common reducing agent in chemical synthesis. Samarium has no significant biological role but is only slightly toxic.
Terbium is a chemical element with the symbol Tb and atomic number 65. It is a silvery-white, rare earth metal that is malleable, ductile, and soft enough to be cut with a knife. The ninth member of the lanthanide series, terbium is a fairly electropositive metal that reacts with water, evolving hydrogen gas. Terbium is never found in nature as a free element, but it is contained in many minerals, including cerite, gadolinite, monazite, xenotime, and euxenite.
Ytterbium is a chemical element with the symbol Yb and atomic number 70. It is the fourteenth and penultimate element in the lanthanide series, which is the basis of the relative stability of its +2 oxidation state. However, like the other lanthanides, its most common oxidation state is +3, as in its oxide, halides, and other compounds. In aqueous solution, like compounds of other late lanthanides, soluble ytterbium compounds form complexes with nine water molecules. Because of its closed-shell electron configuration, its density and melting and boiling points differ significantly from those of most other lanthanides.
Monazite is a reddish-brown phosphate mineral containing rare-earth metals. It occurs usually in small isolated crystals. It has a hardness of 5.0 to 5.5 on the Mohs scale of mineral hardness and is relatively dense, about 4.6 to 5.7 g/cm3. There are at least four different kinds of monazite, depending on relative elemental composition of the mineral:
The mineral bastnäsite (or bastnaesite) is one of a family of three carbonate-fluoride minerals, which includes bastnäsite-(Ce) with a formula of (Ce, La)CO3F, bastnäsite-(La) with a formula of (La, Ce)CO3F, and bastnäsite-(Y) with a formula of (Y, Ce)CO3F. Some of the bastnäsites contain OH− instead of F− and receive the name of hydroxylbastnasite. Most bastnäsite is bastnäsite-(Ce), and cerium is by far the most common of the rare earths in this class of minerals. Bastnäsite and the phosphate mineral monazite are the two largest sources of cerium and other rare-earth elements.
Praseodymium is a chemical element with the symbol Pr and atomic number 59. It is the third member of the lanthanide series and is traditionally considered to be one of the rare-earth metals. Praseodymium is a soft, silvery, malleable and ductile metal, valued for its magnetic, electrical, chemical, and optical properties. It is too reactive to be found in native form, and pure praseodymium metal slowly develops a green oxide coating when exposed to air.
Europium(III) chloride is an inorganic compound with the formula EuCl3. The anhydrous compound is a yellow solid. Being hygroscopic it rapidly absorbs water to form a white crystalline hexahydrate, EuCl3·6H2O, which is colourless. The compound is used in research.
Naturally occurring europium (63Eu) is composed of 2 isotopes, 151Eu and 153Eu, with 153Eu being the most abundant (52.2% natural abundance). While 153Eu is observationally stable, 151Eu was found in 2007 to be unstable and undergo alpha decay. The half-life is measured to be (4.62 ± 0.95(stat.) ± 0.68(syst.)) × 1018 y which corresponds to 1 alpha decay per two minutes in every kilogram of natural europium. Besides the natural radioisotope 151Eu, 36 artificial radioisotopes have been characterized, with the most stable being 150Eu with a half-life of 36.9 years, 152Eu with a half-life of 13.516 years, 154Eu with a half-life of 8.593 years, and 155Eu with a half-life of 4.7612 years. The majority of the remaining radioactive isotopes have half-lives that are less than 12.2 seconds. This element also has 17 meta states, with the most stable being 150mEu (t1/2 12.8 hours), 152m1Eu (t1/2 9.3116 hours) and 152m2Eu (t1/2 96 minutes).
The Europium anomaly is the phenomenon whereby the europium (Eu) concentration in a mineral is either enriched or depleted relative to some standard, commonly a chondrite or mid-ocean ridge basalt (MORB). In geochemistry a europium anomaly is said to be "positive" if the Eu concentration in the mineral is enriched relative to the other rare-earth elements (REEs), and is said to be "negative" if Eu is depleted relative to the other REEs.
Yttrium is a chemical element with the symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a "rare-earth element". Yttrium is almost always found in combination with lanthanide elements in rare-earth minerals, and is never found in nature as a free element. 89Y is the only stable isotope, and the only isotope found in the Earth's crust.
Cerium is a chemical element with the symbol Ce and atomic number 58. Cerium is a soft, ductile and silvery-white metal that tarnishes when exposed to air, and it is soft enough to be cut with a knife. Cerium is the second element in the lanthanide series, and while it often shows the +3 oxidation state characteristic of the series, it also exceptionally has a stable +4 state that does not oxidize water. It is also considered one of the rare-earth elements. Cerium has no biological role in humans and is not very toxic.
The Mountain Pass Rare Earth Mine is an open-pit mine of rare-earth elements on the south flank of the Clark Mountain Range, just north of the unincorporated community of Mountain Pass, California, United States. The mine once supplied most of the world's rare-earth elements. Owned by MP Materials, it is the only rare earth mining and processing facility in the United States.
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