All practice pages/Interatomic theory/Elements
Element 69, a lanthanide
Named for the mythical far north, it is one of the rarest of all the rare earth elements.
Period 6, in the lanthanide row set below the main table. The other lanthanides are tinted, and every cell opens its own article.
Thulium has 69 electrons, one for every proton, so the atom carries no charge. Below are the same 69 electrons written two ways.
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹³ 5s² 5p⁶ 6s²
Short form: [Xe] 4f¹³ 6s², where [Xe] stands for the 54 electrons xenon already has.
That list runs by shell. In the order the subshells fill it reads [Xe] 6s² 4f¹³, because a subshell fills by its energy, not by its shell number.
The simple form counts electrons shell by shell. The orbital form says which subshell each one sits in: s holds 2, p holds 6, d holds 10 and f holds 14. Shell 4 here is 4s² 4p⁶ 4d¹⁰ 4f¹³, and 2 + 6 + 10 + 13 is 31.
Thulium sits in period 6 and has 6 shells. The period number counts the shells.
The outer shell holds 2 electrons. Those are the ones thulium can lose, gain or share, so they are the ones that decide what it bonds with.
Like the other lanthanides, it gives up three electrons to form the Tm³⁺ ion in most of its compounds.
Found in small amounts in monazite, xenotime and ion-adsorption clays.
Per Teodor Cleve found it in 1879 in erbium oxide and named it after Thule, an ancient name for a far northern land, often taken to mean Scandinavia.
Thulium-170 powers portable X-ray devices, thulium lasers are used in surgery, and thulium is studied for superconductors and phosphors. Its rarity and cost keep its uses few.