Erbium spectral lines

Following the adventurous story of terbium it is actually impossible to decide by now who was the true discoverer, Mosander, Delafontaine or Smith The element names, as indicated above were applied inconsistently, and we cannot know whether they referred to the same substance. Did Mosander find the same substance and called it erbium that finally became terbium with Delafontaine, or was Bunsen correct and consequently Mosander s fraction was a mixture only No data were reported that would allow us to state now, at this late date, what substances were identical, no characteristic spectral lines, no exact atomic weight values are at our disposal as yet. 

The transitions in the partly filled 4f shell of lanthanide compounds are sufficiently similar to spectral lines of monatomic entities that the overall, small shift toward lower wave numbers is a rather direct indicator of partly covalent bonding. Hofmann and Kirmreuther (1910) suggested that the electronic orbits had slightly larger radii in Er203 than in hydrated erbium (III) salts, and Ephraim et al. (1926, 1928, 1929) made an extensive systematic study of band shifts in Pr(III), Nd(III) and Sm(III). Such work was continued by Boulanger (1952) and... 

Discovery During 1878-79, PerT. Cleve in Uppsala discovered that erbium contained two other elements. He named them thulium after the old Roman name Thulia for the Furthest North and holmium after Stockholm. Delafontaine and Soret in Switzerland had in fact found lines of a foreign element during the spectral analysis of erbium in 1878. This element, erbium-X or element-X, appeared to be identical with holmium. In tables of discoverers Delafontaine and Soret are mentioned alongside Cleve. 

---