Editing Lanthanide (section)

==Etymology==
The term "lanthanide" was introduced by [[Victor Goldschmidt]] in 1925.<ref>''Skrifter Norske Vidensk-Akad''. (Mat.-nat. Kl.) '''V''':6</ref><ref>{{cite journal|doi=10.1021/ed029p581.2|title=Letters|year=1952|last1=Hakala|first1=Reino W.|journal=Journal of Chemical Education|volume=29|issue=11|page=581|bibcode = 1952JChEd..29..581H |doi-access=free}}</ref> Despite their abundance, the technical term "lanthanides" is interpreted to reflect a sense of elusiveness on the part of these elements, as it comes from the Greek λανθανειν (''lanthanein''), "to lie hidden".<ref>"lanthanide". ''[[Oxford English Dictionary|OED2]]'' 1.14 on CD-Rom. OUP, 1994.</ref> 

Rather than referring to their natural abundance, the word reflects their property of "hiding" behind each other in minerals. The term derives from [[lanthanum]], first discovered in 1838, at that time a so-called new [[rare-earth element]] "lying hidden" or "escaping notice" in a [[cerium]] mineral,<ref>"lanthanum". [[Oxford English Dictionary|''OED2'' v. 1.14]] on CD-Rom. OUP, 1994.</ref> and it is an irony that lanthanum was later identified as the first in an entire series of chemically similar elements and gave its name to the whole series. 

Together with the stable elements of group 3, [[scandium]], [[yttrium]], and [[lutetium]], the [[trivial name]] "[[rare earths]]" is sometimes used to describe the set of lanthanides. The "earth" in the name "rare earths" arises from the minerals from which they were isolated, which were uncommon oxide-type minerals. However, these elements are neither rare in abundance nor "earths" (an obsolete term for water-insoluble strongly basic [[oxide]]s of electropositive metals incapable of being smelted into metal using late 18th century technology). Group 2 is known as the [[alkaline earth]] elements for much the same reason.

The "rare" in the name "rare earths" has more to do with the difficulty of separating of the individual elements than the scarcity of any of them. By way of the Greek ''dysprositos'' for "hard to get at", element 66, [[dysprosium]] was similarly named. The elements 57 (La) to 71 (Lu) are very similar chemically to one another and frequently occur together in nature. Often a mixture of three to all 15 of the lanthanides (along with yttrium as a 16th) occur in minerals, such as [[monazite]] and [[samarskite]] (for which [[samarium]] is named). These minerals can also contain group 3 elements, and actinides such as uranium and thorium.<ref name="autoRefA">"The Elements", Theodore Gray, Black−Dog & Leventhal, Chicago 2007: "Lanthanum" and "Cerium" entries Ch 57 & 58, pp 134–7</ref> A majority of the rare earths were discovered at the same mine in [[Ytterby]], [[Sweden]] and four of them are named (yttrium, ytterbium, erbium, terbium) after the village and a fifth (holmium) after Stockholm; scandium is named after [[Scandinavia]], [[thulium]] after the old name [[Thule]], and the immediately-following group 4 element (number 72) [[hafnium]] is named for the Latin name of the city of [[Copenhagen]].<ref name="autoRefA" />

The properties of the lanthanides arise from the order in which the electron shells of these elements are filled—the outermost (6s) has the same configuration for all of them, and a deeper (4f) shell is progressively filled with electrons as the atomic number increases from 57 towards 71.<ref name="autoRefA" /> For many years, mixtures of more than one rare earth were considered to be single elements, such as [[neodymium]] and [[praseodymium]] being thought to be the single element didymium.<ref>"The Elements", Theodore Gray, Black Dog & Leventhal, Chicago 2007: "Neodymium" and "Praseodymium" entries Ch 59 & 60, pp 138–43</ref> Very small differences in solubility are used in solvent and ion-exchange purification methods for these elements, which require [[Cascade (chemical engineering)|repeated application]] to obtain a purified metal. The diverse applications of refined metals and their compounds can be attributed to the subtle and pronounced variations in their electronic, electrical, optical, and magnetic properties.<ref name="autoRefA" />

By way of example of the term meaning "hidden" rather than "scarce", [[cerium]] is almost as abundant as copper;<ref name="autoRefA" />  on the other hand [[promethium]], with no stable or long-lived isotopes, is truly rare.<ref name="Marshall">{{cite journal |last1=Marshall |first1=James L. Marshall |last2=Marshall |first2=Virginia R. Marshall |title=Rediscovery of the elements: The Rare Earths–The Last Member |journal=The Hexagon |date=2016 |pages=4–9 |url=https://chemistry.unt.edu/sites/default/files/users/owj0001/rare%20earths%20III_0.pdf |access-date=30 December 2019 |archive-date=27 November 2021 |archive-url=https://web.archive.org/web/20211127115101/https://chemistry.unt.edu/sites/default/files/users/owj0001/rare%20earths%20III_0.pdf |url-status=live }}</ref>