| Tecken | Tm |
| Atomnummer | 69 |
| Grupp | - |
| Period | 6 |
| Block | f |
| Ämnesklass | Lantanoid |
| Utseende | Silvery gray |
| Färg | Silver |
| Antal protoner | 69 p+ |
| Antal neutroner | 100 n0 |
| Antal elektroner | 69 e- |
| Fas vid STP | Fast |
| Densitet | 9.32 g/cm3 |
| Relativ atommassa | 168.934 u |
| Smältpunkt | 1818 K 1544.85 °C 2812.73 °F |
| Kokpunkt | 2223 K 1949.85 °C 3541.73 °F |
| Ångbildningsvärme | 191 kJ/mol |
| Elektronegativitet (Paulingskalan) | 1.25 |
| Elektronaffinitet | 99 kJ/mol |
| Oxidationstal | 0, +2, +3 (a basic oxide) |
| Jonisationspotential |
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| Upptäckt och första isolation | Per Teodor Cleve (1879) |
Upptäckten av tulium Thulium was discovered by Swedish chemist Per Teodor Cleve in 1879 by looking for impurities in the oxides of other rare earth elements (this was the same method Carl Gustaf Mosander earlier used to discover some other rare earth elements). Cleve started by removing all of the known contaminants of erbia (Er2O3). Upon additional processing, he obtained two new substances; one brown and one green. The brown substance was the oxide of the element holmium and was named holmia by Cleve, and the green substance was the oxide of an unknown element. Cleve named the oxide thulia and its element thulium after Thule, an Ancient Greek place name associated with Scandinavia or Iceland. Thulium's atomic symbol was initially Tu, but later changed to Tm. | |