Holmium
Holmium is a chemical element with symbol Ho and atomic number 67. Part of the lanthanide series, holmium is a rare earth element. Holmium was discovered by Swedish chemist Per Theodor Cleve.
Identity
- Atomic mass
- 164.93 u
- Category
- Lanthanides
- Group
- 3
- Period
- 6
- Block
- f
- Oxidation States
- +3
- Phase (25 °C)
- Solid
- Appearance
- silvery white
Electronic Structure
- Electron configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f11
- Short configuration
- [Xe] 4f11 6s2
- Electrons per shell
- 2, 8, 18, 29, 8, 2
- Electronegativity (Pauling)
- 1.23
- Electron affinity
- 32.6 kJ/mol
- 1st ionization energy
- 581 kJ/mol
- Ionization energies
- 581 · 1140 · 2204 · 4100 kJ/mol
Physical properties
- Melting point
- 1460.8 °C (1734 K)
- Boiling point
- 2599.8 °C (2873 K)
- Density
- 8.79 g/cm³
- Molar heat capacity
- 27.1 J/(mol·K)
Chemical behavior of holmium
Holmium has eleven outer electrons ([Xe] 4f¹¹ 6s²) and almost always acts as +3, with low electronegativity (1.23). It has the highest magnetic moment among the natural elements and forms highly ionic bonds. It is soft, malleable, oxidizes slowly in dry air and absorbs neutrons efficiently, useful as a burnable poison.
Reactivity
4 Ho + 3 O₂ → 2 Ho₂O₃
In dry air it tarnishes slowly with a pinkish oxide; in moist air the corrosion progresses. When heated, it burns to the oxide.
2 Ho + 6 H₂O → 2 Ho(OH)₃ + 3 H₂
It reacts with water releasing hydrogen, vigorously when hot. The laser garnets that contain it, by contrast, are insoluble and stable.
2 Ho + 6 HCl → 2 HoCl₃ + 3 H₂
It dissolves in acids giving yellow holmium(III) salts. The chloride is the raw material for Ho:YAG garnets and fibers.
Ho + 3 F₂ → 2 HoF₃
With fluorine it gives the fluoride, a precursor of laser crystals and fluorinated glasses for mid-infrared optical fiber.
Notable compounds
| Compound | Formula | Use or importance |
|---|---|---|
| Ho:YAG garnet | Ho:Y₃Al₅O₁₂ | Medical urology laser |
| Holmium oxide | Ho₂O₃ | Lasers and optical standards |
| Holmium fluoride | HoF₃ | Laser crystals and optical fiber |
| Holmium chloride | HoCl₃ | Production of the metal and garnets |
| Holmium boride | HoB₁₂ | Extreme magnetic refrigeration |
Electron shell distribution
View in the atom builderIsotopes
All natural holmium is holmium-165 (¹⁶⁵Ho), with 98 neutrons: it is monoisotopic and stable. Holmium-166m (¹⁶⁶ᵐHo, ~1,200 years) emits very stable gammas and calibrates spectrometers. Holmium-166 (¹⁶⁶Ho, 26.8 hours) emits beta and is used in experimental bone and liver radiotherapy.
Occurrence and production
It appears at about 1.4 ppm in monazite, bastnasite and gadolinite alongside dysprosium and erbium. It does not form minerals of its own. It is obtained by acid dissolution and separation by ion exchange, and the metal by electrolysis or reduction with calcium.
History and origin of the name
Marc Delafontaine and Jacques-Louis Soret caught a glimpse of it in 1878 in erbium and Per Teodor Cleve confirmed it in 1879. They named it holmium, after Holmia, the Latin name of Stockholm: a Swedish tribute in the middle of the rare-earth fever. Its purity was achieved by Urbain and James in the 20th century. Medical lasers took it out of the laboratory.
Applications and relevance of holmium
Uses of the element
As a flux concentrator it raises the field of the most powerful magnets in resonance scanners and accelerators. Its magnetocaloric alloys cool to millikelvin by adiabatic demagnetization for quantum technology and cryogenics.
Uses of its compounds
The Ho:YAG garnet cuts prostate tissue and fragments stones with 2.1-micron light absorbed by water. Doped glasses calibrate spectrophotometers and doped fibers amplify the infrared in sensors.
Health, safety and environment
Biological role
It has no biological function and is considered of low toxicity in the usual forms. In medicine free holmium is not administered: the laser light acts, calibrated and operated by professionals.
Safety
Metallic powder requires control like any combustible dust, with extraction and no flames. Ho:YAG lasers require specific glasses and marked enclosures; the risk is optical, not chemical.
Environment
Its low grade means moving much rock per kilo, with reagent consumption. Its use in surgery avoids open interventions and in cryogenics it replaces scarce helium. Garnet and magnet recycling is starting to recover holmium.
Frequently asked questions about Holmium
What is holmium used for in medical lasers?
Holmium is the active element of Ho:YAG lasers, used in surgery to cut, vaporize or fragment tissue with precision. Its infrared light is effectively absorbed by the water present in the tissues, which allows a localized effect and reduced thermal damage. It is used in urological procedures, such as the fragmentation of urinary stones and prostate enucleation, as well as in other endoscopic interventions.
What role does holmium play in nuclear reactors?
Holmium absorbs neutrons efficiently, so it can be used as a "burnable poison" in nuclear reactors. These materials absorb excess neutrons and help control the chain reaction over time. Its function is to contribute to the stability and safety of the reactor, reducing the reactivity when it is necessary.
Where does holmium come from?
Holmium is found in rare-earth minerals such as monazite, bastnasite and gadolinite, mixed with other lanthanides. Its production involves crushing and processing the ore, followed by separations by ion exchange or solvent extraction. As with other lanthanides, the challenge is not so much its existence in the Earth's crust as its effective separation from chemically very similar elements.
What does holmium have to do with magnetic refrigeration?
Holmium is being researched for magnetic refrigeration, a technology based on the magnetocaloric effect: certain materials change their temperature when subjected to a magnetic field. Holmium compounds can contribute to refrigeration systems by adiabatic demagnetization, capable of reaching extremely low temperatures. This line of research is relevant to low-temperature physics, quantum computing and specialized scientific equipment.
Why is holmium useful in powerful magnets?
Holmium has one of the highest magnetic moments among the natural elements, especially at very low temperatures. This property allows it to be used in pole pieces and magnetic flux concentrators of high-field magnets, where it helps intensify and shape the magnetic field. Although it is not the usual material of commercial magnets, it is valuable in scientific equipment and applications that require very controlled magnetic fields.
Is holmium dangerous?
Holmium has no known biological function and is considered of low toxicity in the usual forms and exposures studied. Even so, the metal and some compounds may require industrial precautions, especially in the form of fine powder. In medicine, elemental holmium is not administered; it is used in laser equipment that is correctly calibrated and operated by professionals.
What is holmium used for in spectroscopy and calibration?
The isotope holmium-166m has a very long half-life and emits a wide range of gamma rays, so it is used to calibrate gamma spectrometers. Holmium-doped filters and glasses are also used as calibration standards in spectrophotometry. These applications take advantage of its well-defined spectral emissions to check the accuracy of optical and radiological measurement instruments.
Main sources consulted: PubChem, Royal Society of Chemistry, NIST, IUPAC. Last revision: November 2026.