Rare earth elements ("REEs") are a set of seventeen chemical elements. They include the fifteen lanthanides plus scandium and yttrium. Scandium and yttrium are rare earth elements since they are often found in the same ore deposits as the lanthanides and have similar chemical properties.
Although they are called rare, rare earth elements are not extremely rare on Earth. They were called this because they are spread very evenly over the Earth, so it is hard to find a lot in one place. Promethium is rare, because it is radioactive, and decays.
Cerium, one of the lanthanides, is the 25th most common element in the Earth's crust. However, most rare earth elements are not found concentrated or in pure forms.
List of rare earth elements
This is a table of the seventeen rare earth elements, their atomic number and symbol, the origin of their names, and some of their uses. Some of the rare earths are named after the scientists who discovered them, and some are named based on where they were discovered. { | class="wikitable sortable" |- !Z !Symbol !Name ! class="unsortable"|Name Origin ! class="unsortable"|Selected applications |- |21 |Sc |Scandium |from Scandinavia, where the first rare earth ore was discovered. |Light aluminium-scandium alloy is used for aerospace components. It is also an additive in certain lamps.<ref name="CRC_ed89_elements">C.R. Hammond, "Section 4; The Elements", in CRC Handbook of Chemistry and Physics, 89th edition (internet version 2009), David R. Lide, ed. CRC Press/Taylor and Francis, Boca Raton, FL.</ref> |- |39 |Y |Yttrium |after the village of Ytterby, Sweden, where it was discovered. |Yttrium is found in certain lasers and TV phosphors. It also has applications in high-temperature superconductors, and microwave filters., energy-efficient light bulbs |- |57 |La |Lanthanum |from the Greek "lanthanein", meaning to be hidden. |High refractive index glass, flint, hydrogen storage, battery-electrodes, camera lenses, fluid catalytic cracking catalyst for oil refineries |- |58 |Ce |Cerium |after the dwarf planet Ceres, named after the Roman goddess of agriculture. |Chemical oxidizing agent, polishing powder, yellow colors in glass and ceramics, catalyst for self-cleaning ovens, fluid catalytic cracking catalyst for oil refineries, flints for lighters |- |59 |Pr |Praseodymium |from the Greek "prasios", meaning leek-green, and "didymos", meaning twin. |Rare-earth magnets, lasers, core material for carbon arc lighting, colorant, additive in glass used in welding goggles, |- |60 |Nd |Neodymium |from the Greek "neos", meaning new, and "didymos", meaning twin. |Rare-earth magnets, lasers, violet colors in glass and ceramics, ceramic capacitors |- |61 |Pm |Promethium |after the Titan Prometheus, who brought fire to mortals. |Atomic batteries |- |62 |Sm |Samarium |after Vasili Samarsky-Bykhovets, who discovered the rare earth ore samarskite. |Rare-earth magnets, lasers, |- |63 |Eu |Europium |after the continent of Europe. |Red and blue phosphors, lasers, mercury-vapor lamps, |- |64 |Gd |Gadolinium |after Johan Gadolin (1760–1852), to honor his investigation of rare earths. |Rare-earth magnets, high refractive index glass or garnets, lasers, X-ray tubes, computer memories, neutron capture, MRI contrast agents |- |- |65 |Tb |Terbium |after the village of Ytterby, Sweden. |Green phosphors, lasers, fluorescent lamps |- |66 |Dy |Dysprosium |from the Greek "dysprositos", meaning hard to get. |Rare-earth magnets, lasers |- |67 |Ho |Holmium |after Stockholm (in Latin, "Holmia"), native city of one of its discoverers. |Lasers |- |68 |Er |Erbium |after the village of Ytterby, Sweden. |Lasers, vanadium steel |- |69 |Tm |Thulium |after the mythological northern land of Thule. |Portable X-ray machines |- |70 |Yb |Ytterbium |after the village of Ytterby, Sweden. |Infrared lasers, chemical reducing agent |- |71 |Lu |Lutetium |after Lutetia, the city which later became Paris. |Medical devices, high refractive index glass |}
Origin
Rare earth elements are heavier than iron. They are made by supernovae (exploding stars). In nature, fission of uranium-238 creates very small amounts of radioactive promethium. Most promethium is synthetically created in nuclear reactors.
Rare earth elements change through time in small quantities (ppm, parts per million). Their proportion can be used for geologic dating and dating fossils.