Thulium: the essentials
- Name: thulium
- Symbol: Tm
- Atomic number: 69
- Relative atomic mass (Ar): 168.93422 (2)
- Standard state: solid at 298 K
- Appearance: silvery white
- Classification: Metallic
- Group in periodic table:
- Group name: Lanthanoid
- Period in periodic table: 6 (lanthanoid)
- Block in periodic table: f
- Shell structure: 22.214.171.124.8.2
- CAS Registry: 7440-30-4
Thulium atoms have 69 electrons and the shell structure is 126.96.36.199.8.2. The ground state electronic configuration of neutral thulium is [Xe].4f13.6s2 and the term symbol of thulium is 2F7/2.
Thulium is the least abundant of the earth elements, and is about as rare as silver, gold, or cadmium.
The pure metal has a bright, silvery lustre. It is reasonably stable in air, but the metal must be protected from moisture. The element is silvery-grey, soft, malleable, and ductile, and can be cut with a knife. It is a rare earth metal found in minerals such as monazite.
This sample is from The Elements Collection, an attractive and safely packaged collection of the 92 naturally occurring elements that is available for sale.
Thulium: physical properties
- Density of solid: 9321 kg m-3
- Molar volume: 19.13 cm3
- Thermal conductivity: 17 W m‑1 K‑1
Thulium: heat properties
- Melting point: 1818 [1545 °C (2813 °F)] K
- Boiling point: 2223 [1950 °C (3542 °F)] K
- Enthalpy of fusion: 20.5 kJ mol-1
Thulium: atom sizes
- Atomic radius (empirical): 175 pm
- Molecular single bond covalent radius: 164 (coordination number 3) ppm
- van der Waals radius: 280 ppm
- Pauling electronegativity: 1.25 (Pauling units)
- Allred Rochow electronegativity: 1.11 (Pauling units)
- Mulliken-Jaffe electronegativity: (no data)
Thulium: orbital properties
- First ionisation energy: 596.70 kJ mol‑1
- Second ionisation energy: 1164.1 kJ mol‑1
- Third ionisation energy: 2280 kJ mol‑1
- Universe: 0.1 ppb by weight
- Crustal rocks: 450 ppb by weight
- Human: (no data) ppb by weight
Thulium: crystal structure
Thulium: biological data
- Human abundance by weight: (no data) ppb by weight
Thulium has no biological role but is said to stimulate the metabolism.
Reactions of thulium as the element with air, water, halogens, acids, and bases where known.
Thulium: binary compounds
Binary compounds with halogens (known as halides), oxygen (known as oxides), hydrogen (known as hydrides), and other compounds of thulium where known.
Thulium: compound properties
Bond strengths; lattice energies of thulium halides, hydrides, oxides (where known); and reduction potentials where known.
Thulium: historyThulium was discovered by Per Theodore Cleve in 1879 at Sweden. Origin of name: named after ""Thule", an ancient name for Scandinavia.
Isolation: thulium metal is available commercially so it is not normally necessary to make it in the laboratory, which is just as well as it is difficult to isolate as the pure metal. This is largely because of the way it is found in nature. The lanthanoids are found in nature in a number of minerals. The most important are xenotime, monazite, and bastnaesite. The first two are orthophosphate minerals LnPO4 (Ln deonotes a mixture of all the lanthanoids except promethium which is vanishingly rare) and the third is a fluoride carbonate LnCO3F. Lanthanoids with even atomic numbers are more common. The most comon lanthanoids in these minerals are, in order, cerium, lanthanum, neodymium, and praseodymium. Monazite also contains thorium and ytrrium which makes handling difficult since thorium and its decomposition products are radioactive.
For many purposes it is not particularly necessary to separate the metals, but if separation into individual metals is required, the process is complex. Initially, the metals are extracted as salts from the ores by extraction with sulphuric acid (H2SO4), hydrochloric acid (HCl), and sodium hydroxide (NaOH). Modern purification techniques for these lanthanoid salt mixtures are ingenious and involve selective complexation techniques, solvent extractions, and ion exchange chromatography.
Pure thulium is available through the reduction of TmF3 with calcium metal.
2TmF3 + 3Ca → 2Tm + 3CaF2
This would work for the other calcium halides as well but the product CaF2 is easier to handle under the reaction conditions (heat to 50°C above the melting point of the element in an argon atmosphere). Excess calcium is removed from the reaction mixture under vacuum.