Ytterby Mine on the island of Resarö, in Vaxholm Municipality in Stockholm archipelago
4 August 2023
Erbium (atomic number 68, symbol Er) and terbium (atomic number 65, symbol Tb) are two of the four elements named after the Swedish mining village of Ytterby, the others being yttrium and ytterbium. But the history of the names is more convoluted than the simple etymology suggests.
In 1843 chemist Carl Gustaf Mosander discovered that a sample of the oxide of yttrium in his possession also contained two other oxides which he dubbed erbium and terbium. He identified the erbium oxide as having a yellowish color and terbium oxide a reddish one:
If the name of yttria be reserved for the strongest of these bases, and the next in order receives the name of oxide of terbium, while the weakest be called oxide of erbium, we find the following characteristic differences distinguishing the three substances. […] Oxide of terbium, the salts of which are of a reddish colour, appears, when pure, to be devoid of colour, like yttria. Oxide of erbium differs from the two former in its property of becoming of a dark orange yellow colour when heated in contact with air.
But in 1860, chemist and physician Nils Johan Berlin conducted a spectroscopic analysis of the ore and only found the red- or rose-colored oxide. Based on his analysis, Berlin disputed the existence of the other oxide, and he confusingly dubbed the red oxide (Mosander’s terbium) erbium. In 1877, Chemist Marc Delafontaine conclusively showed that the yellow oxide did indeed exist, but he followed Berlin’s switch in naming and dubbed the yellow oxide terbium. Delafontaine had previously suggested the yellow oxide be named mosandrium, but that name did not stick. As a result, the present-day nomenclature of the two elements is the reverse of Mosander’s original.
Sources:
Miśkowiec, Pawel. “Name Game: The Naming History of the Chemical Elements: Part 2—Turbulent Nineteenth Century.” Foundations of Chemistry, 8 December 2022. DOI: 10.1007/s10698-022-09451-w.
Mosander, C.G. “On the New Metals, Lanthanium and Didymium, Which Are Associated with Cerium; and on Erbium and Terbium, New Metals Associated with Yttria.” London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, third series. 23.152, October 1843, 241–254 at 252.
Oxford English Dictionary, second edition, 1989, s.v. erbium, n.
Photo credit: Sinikka Halme, 2019. Wikimedia Commons. Licensed under a Creative Commons Attribution-Share Alike 4.0 International license.