1. Thulium-165
  2. Thulium Element
  3. Thulium Periodic Table
  4. Thulium Facts For Kids

Thulium was discovered in 1879. It is slowly tarnished in air but is more resistant to oxidation than other rare earth metals. Thulium is used as radiation source in portable X-ray devices.

  • Thulium is a chemical element with symbol Tm and atomic number 69. It is the thirteenth and third-last element in the lanthanide series. Like the other lanthanides, the most common oxidation state is +3, seen in its oxide, halides and other compounds; because it occurs so late in the series, however, the +2 oxidation state is also stabilized by the nearly full 4f shell that results.
  • Figure 6: Level scheme of thulium (Tm 3+) ions in ZBLAN fiber, showing how excitation with an 1140-nm laser can lead to blue fluorescence and laser emission. The fiber laser concept is most suitable for the realization of upconversion lasers, as these often have to operate on relatively “difficult” laser transitions, requiring high pump intensities.
  • The I-PSS is based on the answers to seven questions concerning urinary symptoms. Each question is assigned points from 0 to 5 indicating increasing severity of the particular symptom.

History and Discovery

Order exciting merchandise emblazoned with the Case's Ladder's logo! Merchandise.

Thulium was discovered in 1879 by Per Teodor Cleve. He followed the same method of Carl Gustaf Mosander to find the impurities in the oxides of rare earth element. He found two substance one brown and other one is green in color and named the brown one holmium and green substance called thulia later called thulium after Thule, an Ancient Greek place name popular and associated with Scandinavia. Earlier its atomic symbol was Tu but it was changed to Tm [1]. Through repetition of bromate fractional crystallization Charles James manufactured first pure thulium in 1911. Commercially it was first prepared in late 1950s through ion exchange separation technology.




Periodic Table ClassificationGroup n/a
Period 6
State at 20CSolid
ColorSilvery gray
Electron Configuration[Xe] 4f13 6s2
Electron Number69
Proton Number69
Electron Shell2, 8, 18, 31, 8, 2
Density9.32 at 20°C
Atomic number69
Atomic Mass168.93 g.mol -1
Electronegativity according to Pauling1.25


Thulium is second least abundant element of the lanthanide series after promethium. Its abundance in earth crust is about 0.5 mg/kg by weight and 50 parts per million by moles. It makes up to 0.5 parts per million of soil and 250 parts per quadrillion of seawater. Thulium is about 200 parts per trillion by weight in the solar system and 1 part per trillion by moles [2]. Naturally thulium is not present in pure form but it is present in small quantities in minerals along with other rare earth elements. Mostly it is present in minerals which contain yttrium and gadolinium, particularly it occurs in the mineral gadolinite. It is also found in the minerals monazite, xenotime and euxenite. The main deposits of thulium main deposits are present in China; however, it is also present in Australia, Brazil, Greenland, India, Tanzania and the United States.

Physical Characteristics

Thulium in pure form has silvery luster and is a bright metal. Thulium metal can be cut with knife and has ability of deformation. It has two allotropes: tetragonal α-Tm and the stable hexagonal β-Tm. It is ferromagnetic at temperature below 32 K and antiferromagnetic between 32 and 56 K. Thulium is paramagnetic above 56 K. Thulium has chemical symbol Tm with atomic number 69. Its atomic weight is 168.934. Thulium melting point is 1545OC and boiling point is 1950OC. Its density is very high and at room temperature it is about 9.32 g/cm3 [3].

Chemical Characteristics

Thulium is a reactive metal. When exposed to air and water it is tarnished slowly. It speedily burns at 150OC and form thulium (lll) oxide. It is electropositive and react slowly with cold water and quickly with hot water and formed thulium hydroxide. It also react slowly with halogens at room temperature but vigorously above 200OC to form TmF3 (white), TmCl3 (yellow), TmBr3 (white) and TmI3 (yellow). Thulium dissolves in dilute sulfuric acid and form pale green Tm (lll) ions. It reacts with metallic and non-metallic elements and formed binary compounds like: TmN, TmS, TmC2, TmH2, TmH3, TmSi2, TmB4. Thulium mostly exist in +2 and +3 oxidation states. Tm3+ ions shows bright blue luminescence. Thulium oxide called ‘’thulia’’ (Tm2O3). It react with hydrogen chloride and produce hydrogen gas and thulium chloride. It also reacts with nitric acid and form thulium nitrate [4].

Significance and Uses

  • Thulium is used in portable X-rays device that has been bombarded in a nuclear reactor as a radiation source.
  • Holmium- chromium-thulium doped in YAG (yttrium aluminum garnet) is an active laser medium. It has high efficiency.
  • Thulium-170 is used for cancer treatment via brachytherapy (radiotherapy).
  • Thulium-170 is also used as popular radioisotopes for use in industrial radiography.
  • It is also used in high temperature super conductors like yttrium.
  • It has potential to use in ferrites (ceramic material: mixing iron (lll) oxide with small portion of metallic mineral), ceramic magnetic material which are used in microwave equipment.
  • Like scandium it is also used in arc lighting.
  • Thulium is also used in euro banknotes against counterfeiting (fake or unauthorized replicas).
  • Thulium- doped calcium sulfate is used in personal radiation dosimeters.

Health Effects

Thulium in the form of soluble salts are slightly toxic but insoluble are nontoxic. Thulium is present in the liver, kidneys and bones in high amount. Thulium in the form of dust and powder are toxic when inhaled or ingested. Thulium in powdered form can be explosive. Its radioactive isotopes can cause radiation poisoning.


Isotopes of Thulium

Thulium isotopes range in atomic masses from 145 to 179. Thulium-169 is considered the stable isotope. Thulium-171 is also longest lived isotope and has half-life of 1.92 years. Thulium-170 has 128.6 days. Other isotopes have half- lives of few minutes or may be less.


[1]. Eagleson, Mary (1994). Concise Encyclopedia Chemistry. Walter de Gruyter. p. 1061. ISBN978-3-11-011451-5.

[2]. Thulium. Retrieved on 2013-03-29.


[4]. “Chemical reactions of Thulium”. Webelements. Retrieved 2009-06-06.

Other Periodic Table Elements

  • Manganese

    Manganese is an ancient metal and was discovered as a distinct element in 1774. It…

  • Cobalt

    Cobalt is transition metal and was discovered in pure form in 1735. It is essential…


    Silver is one of the seven metals of antiquity and have been considered precious throughout…

Prove - and improve - your social media ROI and business value

Differentiate your brand on social media and drive the right results

Make your company #1 on social media in your peer group

We are Thulium
Data-driven strategies and award-winning storytelling

Thulium is a social media marketing agency focused on your social media investment. Through proprietary data analytics and award-winning storytelling on social media, we make social work for our clients.

That company became Thulium. Since then, we’ve expanded into a full-service, social media marketing agency with a team of social media experts, designers, writers, and creative innovators. We’re obsessed with digital transformation and the challenges it brings to the incredibly complex, and often chaotic digital marketing place. Our goal is to envision what’s next, rather than what’s new, and be on the cutting edge with a future-forward.

Snagit powerpoint presentation. With TechSmith Smart Player for Office, you can seamlessly integrate interactive content made with TechSmith products like Camtasia and Snagit into your PowerPoint and Excel documents right from OneDrive for Business and SharePoint Online. Snagit makes it simple to grab vertical and horizontal scrolls, infinitely scrolling webpages, long chat messages, and everything in between. Grab Text Extract the text from a screen capture or file and quickly paste it into another document for edits.

Thulium Services
Social Media Analytics

Prove and improve your social media ROI and business value.

Social Media Strategy

Thulium Element

Differentiate your brand on social media and drive the right results.

Influencer Programs

Partner with the truly influential people in your market to be #1 in your peer group on social media.

Thulium Periodic Table

Our clients include exceptional global brands such as:

Thulium Facts For Kids

Our clients include exceptional global brands such as: