Thulium: Properties & Uses

Thulium is a chemical element that belongs to the Lanthanide series, which is in the sixth period of the periodic table, and its symbol is Tm. It is an f-block element, and its atomic number is 69 in the periodic table. 

• Thulium is classified as a rare earth metal and is discovered in the earth's crust. 
• Lanthanide metals include erbium and ytterbium.
• It is rarely found in pure form in nature. 
• Like other lanthanides and rare earth metals, it has an oxidation state of +3. 
• Thulium is not a hard metal and has a silvery grey look. 
• You can easily cut this metal with a knife. 
• It is ductile and has high corrosion resistance.
• We can easily find the thulium compound in everyday life, which includes using the metal in portable X-ray devices.

Key Terms: Thulium, Periodic Table, Lanthanide Metals, Oxidation State, Corrosion, Resistance, f-Block Element, Isotopes, Electronic Configuration, Thulium Oxide, Protons, Nucleus

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What is Thulium?

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Thulium is a chemical compound that is the thirteenth and third-last element found in the Lanthanide metals series. When we place this metal in an aqueous solution, it forms coordination complexes with nine water molecules.

• Thulium is considered the second-least abundant element of the Lanthanide series.
• It is highly stable in air and can be easily dissolved in acids.
• However, the result is different if you compare this metal with hydrofluoric acid (HF).
• When thulium reacts with hydrofluoric acid, a layer of insoluble trifluoride (TmF₃) is formed on the surface.
• You can also use this metal in devices that detect defects in electronic components.

Thulium

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Discovery of Thulium

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Thulium was founded by Swedish scientist Per Teodor Cleve. In 1879, while working with erbia (erbium oxide) in Uppsala, Sweden, Per Teodor Cleve found two new compounds: green and brown. 

• When he analyzed both the elements, they were found to be thulium and holmium oxides.
• He named the green substance thulia, which was subsequently discovered to be thulium oxide.
• The brown substance was named holmia, which was later discovered to be holmium oxide.
• The element's name is derived from 'Thule,' an ancient Scandinavian name.
• Cleve's discovery was comparable to that of Carl Gustaf Mosander, a Swedish scientist.
• In 1843, Mosander discovered erbium and terbium.
• In 1911, Charles James of New Hampshire used the 'James Method' to produce the first pure thulium.
• He repeatedly used the bromate fractional crystallization method.

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Isotopes and Electronic Configuration of Thulium

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The isotopes of thulium range from thulium-145 to thulium-179. Thulium-169 is the most stable isotope, which is found in abundance. It is expected to decay and create 165H_o, which has an extremely long half-life. 

• With a half-life of 1.92 years, its synthetic isotope, thulium-171, is also extremely stable. 
• Other synthetic isotopes with half-life durations of 9.25 days, 93.1 days, and 128.6 days are thulium–167, thulium–168, and thulium–170.
• Thulium has an atomic number of 69, and its electronic configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f¹³ 5d⁰ 6s² or Xe 4f¹³ 6s².
• It has 2 electrons in the K-shell and 8 electrons in the L-shell.
• In addition, it has 18 electrons in the M-shell and 31 electrons in the N-shell.
• The other 8 electrons are located in the O-shell, and 2 electrons are in the P-shell.

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Structure of Thulium

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Thulium is an organic compound that forms a closely packed hexagonal structure. The atoms within the compound are joined by a double bond. Within the nucleus, there are 69 protons and 100 electrons.

• The bond between the oxygen atom is shorter in length.
• The electrons found in the octahedral species are rotating with low spin.
• These compounds are called neutral heteroatomic molecules in the gas phase.

Structure of Thulium 

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Properties of Thulium

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The important properties of thulium are as follows:

• The nucleus of the thulium element contains 69 protons.
• The energy of its initial ionization is 596.7 kJ.mol^-1.
• There are two major allotropes of thulium: alpha and beta. 
• The shape of alpha thulium is tetragonal, while the shape of beta thulium is hexagonal.
• Thulium tarnishes when exposed to air. 
• It has a wavelength of 2080 nm and is employed in military applications, medicine, and meteorology.
• However, you can use thulium for a longer duration as the compound is corrosion-resistant and tarnishes slowly.
• It has an electronegativity of 1.25 on the Pauling scale.

The properties of thulium is further divided into physical and chemical properties of element which are as follows:

Physical Characteristics of Thulium

The physical properties of thulium are as follows:

• Thulium is a lustrous silvery-grey metal.
• It is a delicate metal which is highly ductile and malleable.
• The compound is solid at room temperature.
• It has a melting point of 1545 degrees Celsius
• The boiling point of a compound is 1950 degrees Celsius.
• It will form a hexagonal crystal structure in which molecules are densely packed.
• The oxide of thulium is basic in nature.
• At specified temperatures, it exhibits ferromagnetic, antiferromagnetic, and paramagnetic characteristics. 
• It has ferromagnetic characteristics at 32 K and antiferromagnetic properties between 32 and 56 K. 
• Thulium exhibits paramagnetic properties at temperatures over 56 K.

The table below highlights the important properties of thulium which are as follows:

Chemical Properties of Thulium

The chemical properties of thulium are as follows:

Chalcogens

It creates thulium chalcogenides when it reacts with chalcogens.

Reaction with Water

Thulium is hydrolyzed by both cold and hot water in its reaction with water. Although it reacts slowly when you expose thulium to cold water, it reacts quickly when exposed to hot water. When it reacts with water, it produces thulium hydroxide. 

2Tm(s) + 6H₂O(l) → 2Tm(OH)₃(aq) + 3H₂(g)

Reaction with Oxide

Thulium burns quickly at 150 degrees Celsius, forming the oxide Tm₂O₃.

4Tm + 3O₂ → 2Tm₂O₃

Reaction with Halides

Thulium creates thulium halides when it reacts with halogens. With different halogens, it generates various coloured halides. Thulium fluoride, for example, is white in appearance, but thulium iodide is yellow.

• The temperature is important in these thulium-halogen interactions.
• Thulium reacts slowly with halogens at ambient temperature, but rapidly with halogens at higher temperatures (> 200 °C).
• Water interacts vigorously with thulium dichloride (thulium halide). 

TmCl₂ + H₂O ------→ Tm(OH)₃ + H₂

Reaction with Sulfuric Acid

In dilute sulfuric acid, thulium dissolves to form a pale green solution containing T_m+3 ions.

2Tm(s) + 3H₂SO₄(aq) → 2Tm³⁺ (aq) + 3SO₂⁻⁴ (aq) + 3H₂(g)

Reaction with Hydrochloric Acid

When thulium interacts with HCl, it produces hydrogen gas and thulium chloride.

Tm + 2HCl -----> TmCl₂ + H₂

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Uses of Thulium

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Thulium is a rare earth metal that is both expensive and scarce. As a result, it has a few uses which are as follows:

• When thulium is blasted in a nuclear reactor, the radioactive isotope ₁₇₀Tm is created.
• It is utilized as a portable source of X-rays and has a half-life of 128 days.
• We can use thulium to dope yttrium aluminium garnets (YAG).
• The compound is visible in rare earth metal alloys.
• If you are not aware, thulium is used in euro banknotes because of its blue fluorescence colour under UV light.
• With holmium, chromium, and yttrium aluminium garnet, it is used as an active laser medium material in lasers.
• Thulium is used in X-ray machines that are used to diagnose medical and dental problems. 
• In cancer treatment, ₁₇₀Tm is employed in X-ray equipment.
• In the case of industrial radiography, we can use ₁₇₀Tm.
• It can also be employed in superconductors that operate at high temperatures.

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Things to Remember

• Thulium is a chemical compound that has a low-to-moderate acute toxicity rating, unlike the other lanthanides.
• Natural thulium is utilized in microwave equipment and can be used to dope fibre lasers in ceramic magnetic materials.
• It could be used as a radiation source in portable X-ray equipment after being used for bombardment in nuclear reactors.
• Thulium is considered suitable for ceramic magnetic materials used in microwaves.
• We can use this metal compound to generate electricity.

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