Thulium

=Thulium= Thulium is a chemical element that has the symbol **Tm** and atomic number 69. Thulium is the second least abundant of the lanthanides (promethium is only found in trace quantities on Earth). It is an easily workable metal with a bright silvery-gray luster. Despite its high price and rarity, thulium is used as the radiation source in portable X-ray devices and in solid-state lasers.
 * Atomic Number:** 69
 * Atomic Weight:** 168.93421
 * Melting Point:** 1818 K (1545°C or 2813°F)
 * Boiling Point:** 2223 K (1950°C or 3542°F)
 * Density:** 9.32 grams per cubic centimeter
 * Phase at Room Temperature:** Solid
 * Element Classification:** Metal
 * Period Number:** 6 **Group Number:** none **Group Name:** Lanthanide
 * What's in a name?** From the earliest name for Scandinavia, **Thule**.
 * Say what?** Thulium is pronounced as **THOO-lee-em**.
 * History and Uses:** Thulium was discovered by Per Theodor Cleve, a Swedish chemist, in 1879. Cleve used the same method Carl Gustaf Mosander used to discover lanthanum, erbium, and terbium. He looked for impurities in the oxides of other rare earth elements. He started with erbia, the oxide of erbium (Er2O3), and removed all of the known contaminants. After further processing, he obtained two new materials, one brown and the other green. Cleve named the brown material holmia and the green material thulia. Holmia is the oxide of the element holmium and thulia is the oxide of the element thulium. Today, thulium is primarily obtained through an ion exchange process from monazite sand ((Ce, La, Th, Nd, Y)PO4), a material rich in rare earth elements that can contain as much as 0.007% thulium.

Thulium is the least abundant of the naturally occurring rare earth elements. Metallic thulium is relatively expensive and has only recently become available. It currently has no commercial applications, although one of its isotopes, thulium-169, could be used as a radiation source for portable X-ray machines. Thulium forms no commercially important compounds. Some of thulium's compounds include: thulium oxide (Tm2O3), thulium fluoride (TmF3) and thulium iodide (TmI3).
 * Estimated Crustal Abundance:** 5.2×10-1 milligrams per kilogram
 * Estimated Oceanic Abundance:** 1.7×10-7 milligrams per liter
 * Number of Stable Isotopes:** 1
 * Ionization Energy:** 6.184 eV
 * Oxidation State:** +3



Chemical properties
Thulium metal tarnishes slowly in air and burns readily at 150 °C to form thulium(III) oxide: 4 Tm + 3 O2 → 2 Tm2O3 Thulium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form thulium hydroxide: 2 Tm (s) + 6 H2O (l) → 2 Tm(OH)3 (aq) + 3 H2 (g) Thulium reacts with all the halogens. Reactions are slow at room temperature, but are vigorous above 200 °C: 2 Tm (s) + 3 F2 (g) → 2 TmF3 (s) (white)2 Tm (s) + 3 Cl2 (g) → 2 TmCl3 (s) (yellow)2 Tm (s) + 3 Br2 (g) → 2 TmBr3 (s) (white)2 Tm (s) + 3 I2 (g) → 2 TmI3 (s) (yellow) Thulium dissolves readily in dilute sulfuric acid to form solutions containing the pale green Tm(III) ions, which exist as a [Tm(OH2)9]3+ complexes: 2 Tm (s) + 3 H2SO4 (aq) → 2 Tm3+ (aq) + 3 SO 2− 4 (aq) + 3 H2 (g) Thulium reacts with various metallic and non-metallic elements forming a range of binary compounds, including TmN, TmS, TmC2, Tm2C3, TmH2, TmH3, TmSi2, TmGe3, TmB4, TmB6 and TmB12. In those compounds, thulium exhibits valence states +2, +3 and +4, however, the +3 state is most common and only this state has been observed in Tm solutions.

Occurrence and Production
The element is never found in nature in pure form, but it is found in small quantities in minerals with other rare earths. Its abundance in the Earth crust is 0.5 mg/kg. Thulium is principally extracted from monazite (~0.007% thulium) ores found in river sands, through ion-exchange. Newer ion-exchange and solvent-extraction techniques have led to easier separation of the rare earths, which has yielded much lower costs for thulium production. The principal sources today are the ion adsorption clays of southern China. In these, where about two-thirds of the total rare-earth content is yttrium, thulium is about 0.5% (or about tied with lutetium for rarity). The metal can be isolated through reduction of its oxide with lanthanum metal or by calcium reduction in a closed container. None of thulium's natural compounds are commercially important.

Application in Life

 * Laser
 * X-Rays
 * Microwave equipment
 * Hight temperature superconductors

Biological Role
Thulium has no known biological role, although it has been noted that it stimulates metabolism. Soluble thulium salts are regarded as slightly toxic if taken in large amounts, but the insoluble salts are non-toxic. Thulium is not taken up by plant roots to any extent and thus does not get into the human food chain. Vegetables typically contain only one milligram of thulium per tonne (dry weight).