Thulium

Thulium,  ₆₉Tm

A piece of thulium metal from IrC's collection.
General properties
Name, symbol	Thulium, Tm
Appearance	Silvery-gray
Thulium in the periodic table
- ↑ Tm ↓ Md Erbium ← Thulium → Ytterbium
Atomic number	69
Standard atomic weight (Ar)	168.93422(2)
Group, block	, f-block
Period	period 6
Electron configuration	[Xe] 4f13 6s2
per shell	2, 8, 18, 31, 8, 2
Physical properties
Silvery-gray
Phase	Solid
Melting point	1818 K ​(1545 °C, ​​2813 °F)
Boiling point	2223 K ​(1950 °C, ​​3542 °F)
Density near r.t.	9.32 g/cm3
when liquid, at	8.56 g/cm3
Heat of fusion	16.84 kJ/mol
Heat of	191 kJ/mol
Molar heat capacity	27.03 J/(mol·K)
pressure
Atomic properties
Oxidation states	2, 3 ​(a basic oxide)
Electronegativity	Pauling scale: 1.25
energies	1st: 596.7 kJ/mol 2nd: 1160 kJ/mol 3rd: 2285 kJ/mol
Atomic radius	empirical: 176 pm
Covalent radius	190±10 pm
Miscellanea
Crystal structure	​​hexagonal close-packed (hcp)
Thermal expansion	13.3 µm/(m·K) (poly)
Thermal conductivity	16.9 W/(m·K)
Electrical resistivity	676 Ω·m (at 20 °C) (poly)
Magnetic ordering	paramagnetic (300 K)
Young's modulus	74 GPa
Shear modulus	30.5 GPa
Bulk modulus	44.5 GPa
Poisson ratio	0.213
Vickers hardness	470–650 MPa
Brinell hardness	470–900 MPa
CAS Registry Number	7440-30-4
History
Naming	after Thule, a mythical region in Scandinavia
Discovery and first isolation	Per Teodor Cleve (1879)

Thulium is a lanthanide with the symbol Tm and the atomic number 69. Thulium is the second-least abundant of the lanthanides, after radioactively unstable promethium which is only found in trace quantities on Earth.

It is often considered by many chemists a useless element, because it's rare and expensive, and the other more available lanthanides have similar physical and chemical properties.

Properties

Chemical

Thulium metal is a reducing agent and is reactive towards acids and oxidizers. Most ionic thulium compounds are soluble except for the fluoride and the nitrate.

Thulium tarnishes slowly in air and burns readily at 150 °C to form thulium(III) oxide:

4 Tm + 3 O₂ → 2 Tm₂O₃

Thulium reacts slowly with cold water and quite quickly with hot water to form thulium hydroxide:

2 Tm + 6 H₂O → 2 Tm(OH)₃ + 3 H₂

Thulium reacts with all the halogens. Reactions are slow at room temperature, but are vigorous above 200 °C:

2 Tm + 3 X₂ → 2 TmX₃

Physical

Thulium metal has a bright, silvery luster. It slowly tarnishes in air and reacts with water. The metal is soft enough to be cut with a knife. Solutions containing thulium(II) ions often present a wine red coloration. Thulium(III) ions may fluoresce blue under shortwave UV light, though this has not been confirmed.

Availability

Thulium is more common than iodine on Earth, but it is hard to find and extremely expensive. One source for thulium, as well as other rare earth metals, is Metallium. It is sold in 1 gram, 5 gram and 25 gram sizes, as well as rods, ampoules, and coins. Metallium also takes custom orders. Thulium and its compounds may be occasionally found on eBay. Because the Tm(III) ion color is hard to distinguish from other ions, other lanthanides or metals in general may be sold as thulium. This is a common problem with lanthanides, and online sellers.

Occasionally you can find sellers on eBay, like this one.

Projects

• Blue fluorescence (used in Euro banknotes)
• Make ferrite ceramic materials
• Special solid-state lasers

Handling

Safety

Thulium has not been observed to have a biological role, but small amounts of soluble thulium salts stimulate metabolism. Soluble thulium salts are mildly toxic, but insoluble thulium salts are completely nontoxic.

Storage

Thullium should be stored in closed bottles, and kept away from moisture and any corrosive vapors, such as acids.

Disposal

Best to try to recycle it, as it's a rare and expensive material.

References

Relevant Sciencemadness threads

• Thulium(III) color