Per Teodor Cleve

Per Teodor Cleve (1840–1905) was a Swedish chemist and geologist who discovered holmium and thulium and investigated rare-earth elements.

Carl Gustaf Mosander: A Swedish chemist who separated several rare-earth elements from cerium compounds. Mosander’s earlier separations shaped the rare-earth chemistry Cleve later pursued.
Fractional crystallization: A separation method that repeatedly crystallizes a mixture to enrich substances with different solubilities. Cleve used repeated fractionation to separate closely related rare-earth compounds.
Holmium: A metallic chemical element with atomic number 67 and symbol Ho. Cleve identified holmium in 1879 while examining erbia from Scandinavian minerals.
Periodic table: A tabular arrangement of chemical elements ordered by atomic number and recurring chemical properties. Rare-earth discoveries helped expose gaps and classification challenges in the table.
Marc Delafontaine: A Swiss chemist who independently identified holmium in the nineteenth century. Delafontaine’s parallel work complicates the attribution of holmium’s discovery.
Rare-earth elements: A group of 17 chemically similar elements comprising the lanthanides, scandium, and yttrium. Their close chemical similarities made Cleve’s separations unusually difficult.
Thulium: A metallic chemical element with atomic number 69 and symbol Tm. Cleve announced thulium in 1879 after separating it from erbium-containing material.
Dmitri Mendeleev: A Russian chemist who formulated a periodic system of elements and predicted properties of undiscovered elements. Cleve’s element identifications contributed evidence relevant to periodic classification.
Jacques-Louis Soret: A Swiss chemist who studied rare-earth absorption spectra and identified an element later named holmium. Soret detected holmium spectroscopically before Cleve isolated its compounds.
Spectroscopy: The study of how matter interacts with electromagnetic radiation at different wavelengths. Characteristic absorption spectra helped distinguish rare-earth elements in mixtures.

Linked from 3 pages