Last Updated: April 28, 2024


On a fascinating journey through the realm of Thulium, a lesser-known yet incredibly significant element in the periodic table. This complete guide offers a deep dive into the definition, meaning, and myriad uses of Thulium, alongside an exploration of its compounds. With examples to illuminate its role in science and technology, this introduction aims to enrich your understanding of Thulium, highlighting its unique properties and the innovative ways it enriches our world. Perfect for enthusiasts and experts alike, this guide will enhance your knowledge and appreciation of this rare, silvery metal.

What is Thulium ?

Thulium is a chemical element with the symbol Tm and atomic number 69. It is a member of the lanthanide series in the periodic table, a group of elements known as rare earth metals. Thulium is the thirteenth and third-last element in the lanthanide series. Despite its classification as a rare earth element, thulium is fairly abundant in the Earth’s crust, though it is not found in free form in nature. It is usually extracted from minerals such as monazite and xenotime, where it occurs in small amounts.

Thulium has a bright, silvery-gray appearance and is relatively soft and malleable. It can be cut with a knife when pure. The element has a melting point of 1545 degrees Celsius and a boiling point of 1950 degrees Celsius. Among the lanthanides, thulium is noted for its low level of radioactivity; its most stable isotope, Thulium-169, is not radioactive and does not pose a significant risk in terms of radioactivity.

Thulium Formula

  • Formula: Tm
  • Composition: Consists of a single thulium atom.
  • Bond Type: In its elemental form, thulium does not form bonds as it is a pure element. However, thulium can participate in covalent or ionic bonding when reacting with other elements, given its chemical properties as part of the lanthanide series.
  • Molecular Structure: As a pure element, thulium does not present a molecular structure in the traditional sense of compounds. Due to its metallic nature, it is hypothesized that thulium would exhibit a metallic state with a crystalline structure, likely hexagonal close-packed (hcp) or face-centered cubic (fcc), which is common among rare earth metals.
  • Electron Sharing: In compounds, thulium is expected to share electrons covalently or engage in ionic electron transfer with other elements. This behavior is typical of lanthanides, which can form a variety of compounds, displaying both ionic and covalent bonding characteristics.
  • Significance: Thulium’s significance lies in its rarity and specific applications driven by its unique properties among the lanthanides. While not as widely used as some other elements, its applications in certain high-tech areas highlight the importance of even the less abundant rare earth elements.
  • Role in Chemistry: The role of thulium in chemistry includes its use in specialized applications such as in solid-state lasers, portable X-ray devices, and in doping fiber optic cables in telecommunications. Its chemistry is characterized by its +3 oxidation state, typical of lanthanides, but it can also exhibit other oxidation states under certain conditions. Investigations into thulium and its compounds help to broaden our understanding of rare earth chemistry and its application in modern technology.

Atomic Structure of Thulium

Atomic Structure of Thulium

Thulium, in contrast to hydrogen, is a metallic element with established characteristics that include a stable solid form at room temperature and unique properties stemming from its status as a rare earth metal. The behavior of thulium at the atomic and molecular levels significantly diverges from that of hydrogen, given its position as a lanthanide in the periodic table and its metallic characteristics.

Atomic Level: Each thulium atom (Tm) contains 69 protons in its nucleus and is expected to have 69 electrons orbiting around it. The electron configuration of thulium is [Xe] 4f¹³ 6s², indicating a relatively complex electron configuration with a potential for various oxidation states, though +3 is the most common and stable. This indicates a level of chemical reactivity typical of lanthanides and the possibility for forming compounds, particularly with elements that can achieve stable complementary oxidation states.

Molecular Formation: Unlike hydrogen, which forms simple molecules like H₂ through covalent bonding, thulium would not form molecules in a similar manner due to its metallic nature. In bulk form, thulium exhibits a metallic lattice structure typical of metals, involving a hexagonal close-packed (hcp) arrangement. This structure involves metallic bonding, where electrons are delocalized over many thulium atoms, differing fundamentally from the discrete electron sharing seen in hydrogen’s covalent bonds. Thulium’s solid form is stable and can be observed directly, unlike the hypothetical and highly unstable forms of more radioactive elements like bohrium.

Properties of Thulium 

Properties of Thulium 

Physical Properties of Thulium

Property Value
Atomic Number 69
Atomic Mass 168.93422 g/mol
Density 9.32 g/cm³ at 20°C
Melting Point 1545 °C
Boiling Point 1950 °C
State at Room Temperature Solid
Color Silvery gray
Thermal Conductivity 16.9 W/(m·K)
Electrical Resistivity 676 nΩ·m at 20°C

Chemical Properties of Thulium

Thulium, like other lanthanides, exhibits a +3 oxidation state in most of its compounds, indicative of its chemical stability and reactivity. Thulium compounds are generally formed by reacting the metal with various non-metals or by dissolving thulium in acids. Here are some examples illustrating thulium’s chemical properties:

  • Reaction with Oxygen: Thulium reacts with oxygen to form thulium(III) oxide (Tm2O3):

    This oxide is a common starting material for producing other thulium compounds.

  • Reaction with Acids: Thulium dissolves in dilute acids to form solutions containing the Tm(III) ion:

    This demonstrates its reactivity and the ease of forming salts.

  • Formation of Halides: Like other rare earth elements, thulium forms halides, such as thulium(III) chloride (TmCl3), by direct combination with halogens:

Thermodynamic Properties of Thulium

Property Value
Standard Atomic Weight 168.93422 g/mol
Heat of Fusion 16.84 kJ/mol
Heat of Vaporization 251 kJ/mol
Specific Heat Capacity 27.03 J/(mol·K)
Thermal Expansion 13.3 µm/(m·K) at 25°C

Material Properties of Thulium

Property Value
Crystal Structure Hexagonal Close-Packed (hcp)
Hardness Soft (can be cut with a knife)
Modulus of Elasticity 74.0 GPa
Poisson’s Ratio 0.231 (Estimated)
Ductility High, malleable and ductile
Corrosion Resistance Good, especially in dry air

Electromagnetic Properties of Thulium

Property Description
Electrical Resistivity High; about 676 nΩ·m at room temperature
Magnetic Ordering Paramagnetic
Thermal Conductivity 16.9 W/(m·K) at room temperature
Magnetic Susceptibility Positive; paramagnetic at room temperature
Superconducting Point Below 1.5 K, thulium becomes superconducting
Optical Properties Absorbs in the visible and near-infrared; used in lasers

Nuclear Properties of Thulium

Property Description
Natural Isotopes Thulium-169 (100% abundance)
Radioactive Isotopes Tm-170, Tm-171, among others; all synthetic
Nuclear Spin (Tm-169) 1/2
Neutron Cross Section 100 barns for thermal neutrons
Isotope Mass 168.93422 u for Tm-169 (stable isotope)
Half-Life of Most Stable Radioisotope (Tm-171) 1.92 years
Decay Modes Beta decay for radioactive isotopes
Nuclear Quadrupole Moment Thulium nuclei possess a nuclear quadrupole moment, useful in nuclear magnetic resonance (NMR)

Preparation of Thulium

The preparation of thulium, a rare earth element, involves several steps to extract and purify it from its ores. The primary sources of thulium are monazite and xenotime sands, which contain a variety of rare earth elements. The extraction process typically includes:

  1. Ore Processing: The ores are treated with acid (hydrochloric or sulfuric) to convert the rare earth elements into their soluble forms.
  2. Ion Exchange or Solvent Extraction: These methods are used to separate the rare earth elements from each other. Ion exchange chromatography can effectively separate thulium from other lanthanides due to its distinct chemical behavior. Solvent extraction, on the other hand, involves using organic solvents to selectively separate thulium.
  3. Reduction to Metallic Form: The purified thulium is often in the form of thulium oxide (Tm2O3). To convert this to metallic thulium, a reduction process is used, commonly involving calcium or lanthanum as the reducing agents:

Chemical Compounds of Thulium

Chemical Compounds of Thulium (Tm)

  1. Thulium Oxide (Tm2O)
    • Preparation: Obtained by heating thulium in air or by decomposing thulium salts like nitrates or carbonates.
    • Properties: A pale green solid that is insoluble in water. It is used in ceramics and as a dopant for garnet-based lasers and other materials.
  2. Thulium Fluoride (TmF)
    • Preparation: Reacting thulium oxide with hydrofluoric acid.
    • Properties: White crystalline solid, insoluble in water, used in specialized optical glasses due to its low dispersion and non-linear optical properties.
  3. Thulium Chloride (TmCl)
    • Preparation: Direct combination of the elements or by treating thulium oxide with hydrochloric acid.
    • Properties: Hygroscopic, colorless to yellowish solid, soluble in water and ethanol. It’s a starting material for other thulium compounds and in catalysis research.
  4. Thulium Iodide (TmI)
    • Preparation: By reacting thulium metal with iodine.
    • Properties: Bright yellow solid, used in organic synthesis reactions as a catalyst or reagent.
  5. Thulium Nitrate (Tm(NO))
    • Preparation: Dissolving thulium carbonate or oxide in nitric acid.
    • Properties: Water-soluble, crystalline solid, used as a precursor for other thulium compounds and in certain luminescence studies.
  6. Thulium Sulfate (Tm(SO))
    • Preparation: Reaction of thulium oxide with sulfuric acid.
    • Properties: Water-soluble, used in the preparation of other thulium compounds and in various analytical chemistry applications

Isotopes of Thulium

Isotope Mass Number Half-life Primary Decay Mode
Tm-167 167 Stable
Tm-168 168 93 days Electron Capture
Tm-169 169 Stable
Tm-170 170 128.6 days Beta Decay
Tm-171 171 1.92 years Beta Decay
Tm-172 172 63.6 hours Beta Decay
Tm-173 173 8.24 years Beta Decay
Tm-174 174 142 days Beta Decay

Uses of Thulium

Uses of Thulium

  1. Medical Devices: Thulium-170 isotopes are used in portable X-ray machines as they emit X-rays when excited. This application is particularly valuable for medical diagnostics in remote locations.
  2. Solid-State Lasers: Thulium-doped yttrium aluminum garnet (Tm:YAG) lasers are used for surgical procedures, especially in dermatology and urology, due to their ability to be finely tuned to specific wavelengths.
  3. Cancer Treatment: Radioactive thulium isotopes are investigated for their potential in targeted cancer treatment therapies, offering a way to destroy malignant cells with minimal damage to surrounding healthy tissue.
  4. Manufacturing: Thulium’s unique properties are utilized in the production of specialized glass, ceramics, and certain electronic devices, enhancing their performance and efficiency.
  5. Research and Development: Due to its unique electromagnetic properties, thulium is used in scientific research, particularly in studies of magnetic materials and quantum computing.
  6. Nuclear Reactors: Thulium has potential use as a radiation source in nuclear reactors, specifically for testing materials and equipment used in space missions, due to its ability to emit both gamma rays and neutrons.
  7. Doping Material: Thulium is used to dope calcium fluoride, calcium tungstate, and strontium molybdate crystals, improving their efficiency in various applications, including lasers and luminescent materials.
  8. Spectroscopy: Thulium compounds are used as calibration standards for analytical instruments, such as in UV spectroscopy, due to their stable and distinct absorption properties

Production of Thulium

Thulium is one of the least abundant rare earth metals and is primarily extracted from monazite and xenotime ores, which contain small amounts of all the rare earth elements. The production process involves several key steps:

  1. Ore Processing: The ore is treated with acids to produce rare earth chlorides or fluorides.
  2. Solvent Extraction: The rare earth elements are separated from each other using solvent extraction, which exploits differences in their chemical behavior.
  3. Ion Exchange: Further purification is achieved through ion exchange chromatography.
  4. Metallic Reduction: Finally, thulium is produced in its metallic form through the reduction of thulium fluoride with calcium metal, often in an inert atmosphere to prevent oxidation.

Applications of Thulium

Thulium has a variety of specialized applications, owing to its unique properties:

  1. Medical Devices: Thulium is used in portable X-ray machines as it emits X-rays when bombarded with electrons. Its radiation can be used for cancer treatment in certain types of external radiation therapy.
  2. Solid-State Lasers: Thulium-doped yttrium aluminum garnet (Tm:YAG) lasers are used for surgical procedures, especially in dermatology and urology, due to their ability to interact precisely with biological tissues.
  3. Nuclear Reactors: Thulium can absorb nuclear radiation, making it useful as a radiation shield.
  4. Electronic Equipment: Thulium’s compounds are used in the semiconductor industry for doping materials.
  5. Optical Devices: Thulium-doped fiber amplifiers enhance signals in fiber optic cables for telecommunications.
  6. Research and Development: Its isotopes, particularly thulium-170, are used in fundamental research and studies of the material’s properties under extreme conditions.
  7. Decorative Coloring: Thulium oxide is used to color ceramics and glasses.
  8. Magnetic Refrigeration: Thulium’s magnetic properties are exploited in experimental magnetic refrigeration techniques.

Article delves into thulium, outlining its preparation, chemical compounds, and their respective properties and equations. Through detailed exploration, we’ve unveiled thulium’s significant role in technology and science, highlighting its versatility and utility in various fields. Our comprehensive guide illustrates thulium’s contribution to advancements in materials science, showcasing its unique characteristics and the potential for future applications.

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