Thulium is a chemical element in the Periodic Table marked with the atomic number of 69 and with the chemical symbol Tm. This chemical element belongs to period 6 elements and the Lanthanide category. Similar to the rest of the Lanthanide elements Thulium possesses some metallic properties. In the Periodic Table Thulium is preceded by Erbium and is followed by Ytterbium.


Thulium is an extremely rare chemical element and is among the priciest Lanthanides. This chemical element is the second least abundant Lanthanide element in the Periodic Table after Promethium. Thulium is a solid, relatively soft and ductile metallic element, which does not play any biological roles for human beings and other living organisms on Earth. Its toxicity is moderate to none. Thulium has several commercial and scientific applications mainly in lasers and X-ray devices. Similar to other Lanthanides this particular chemical element does not occur in its free state in nature, but is traced in several minerals like xenotime, monazite, and euxenite in combination with other Lanthanide and Rare Earth chemical elements.



Physical Characteristics of Thulium

When it comes to physical characteristics Thulium is a typical Lanthanide element with metallic properties. It is a solid and noteworthy ductile chemical element, which appears with a brilliant silver metallic luster. Its metallic finish tarnishes slowly when Thulium is exposed to air. It is malleable and can be easily cut with a knife. This chemical element is quite electropositive and it dissolves in sulfuric acid. Various Thulium compounds have pale green or reddish-purple ions. Thulium exists in a typical hexagonal close-packed crystal structure and is ferromagnetic at temperatures below 32K, antiferromagnetic at temperatures between 32K and 56K, and paramagnetic at temperatures above 56K. Its melting and boiling points are among the highest melting and boiling points among all Lanthanides – 1818K and 2223K in their respective order.


Chemical Properties of Thulium


Atomic Number – 69

Group – n/a

Period – 6

Block – f

Electronic Configuration – 4f13 6s2

Relative Atomic Mass – 168.9342 (168.93422 g/mol)

Molecular Weight – 168.9342

Electronegativity – 1.25

Density (G CM-3) – 9.32 g/cm3 at room temperature; 8.56 g/cm3 in liquid state

Melting Point – 1818 K; 1545 °C; 2813 °F

Boiling Point – 2223 K; 1950 °C; 3542 °F

Atomic Radius – 176 pm

Isotopes – 1

Electronic Shell – 2, 8, 18, 31, 8, 2


Discovery of Thulium

Thulium was discovered in 1879 by a Swedish chemist, named Per Teodor Cleve. He isolated greenish Thulium oxide from Erbia (Erbium oxide) and named the new oxide Thulia and the element Thulium after the Ancient Greek name Thule, which was once used to describe Scandinavian lands. The very first relatively pure isolation of Thulium was carried out in 1911 by a British chemist, named Charles James. The pure element was fully isolated in the 1950s.


Recognized by: Per Teodor Cleve (1879)

Known and discovered by: Per Teodor Cleve (1879)

Named by: Per Teodor Cleve


Uses and role of Thulium

Thulium does not play any biological role in human beings or other living organisms on Earth. However, it has several scientific and commercial uses mainly in laser manufacturing, X-rays, and electronics like microwaves and radiograph devices.


Despite being extremely rare and expensive, Thulium is actually used in the manufacturing of portable X-ray devices. Thulium lasers have several uses in the medicine industry, in meteorology and in the military. Thulium is also used in the manufacturing of high-temperature superconductors, as well as in various lighting installations. Another noteworthy role of Thulium is as an anti-counterfeiting measure in the manufacturing of Euro banknotes.


Thulium on Earth

Thulium is the second least abundant of all Lanthanide elements on Earth. It is so rare that only traces of it can be found in minerals like monazite, euxenite and xenotime, in combination with other Lanthanide or Rare Earth elements, as it does not occur freely in its natural state on Earth. It can be found in the Earth’s soil and in seawater.



It has been discovered that while Thulium powder has mild toxicity and radiation levels, some Thulium salts can boost up human metabolism if they are administered in small, soluble dosages.