Holmium
Atomic Data
| Atomic Number | 67 |
| Symbol | Ho |
| Atomic Weight | 164.93 u |
| Density (STP) | 8.795 g/cm³ |
| Melting Point | 1460.85 °C (1734 K) |
| Boiling Point | 2719.85 °C (2993 K) |
| Electronegativity | 1.23 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f11 5s2 5p6 6s2 |
| Oxidation States | +3 |
| Phase at STP | Solid |
| Category | Lanthanoid |
| Period / Group | 6 / None |
| CAS Number | 7440-60-0 |
Electron Configuration
[Xe] 4f11 6s2
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 10 | 28 |
| N | 4 | 4s | 2 | 30 |
| N | 4 | 4p | 6 | 36 |
| N | 4 | 4d | 10 | 46 |
| N | 4 | 4f | 11 | 57 |
| O | 5 | 5s | 2 | 59 |
| O | 5 | 5p | 6 | 65 |
| P | 6 | 6s | 2 | 67 |
| Total | 67 | 67 | ||
Isotopes of Holmium
Holmium is monoisotopic: ¹⁶⁵Ho is its only naturally occurring stable isotope, accounting for 100% of all natural Holmium.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Holmium-165 | ¹⁶⁵Ho | 67 | 98 | 100 | Stable |
Abundance & Occurrence
Holmium is present in Earth's crust at approximately 1.3 ppm by mass and at approximately 0.05 ppm by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Dust inhalation: Holmium metal dust and oxide are respiratory irritants; fine particulate inhalation should be controlled with ventilation and appropriate respiratory protection.
- Ho:YAG laser hazard: Holmium-YAG medical and surgical lasers emit at 2.09 µm, which is strongly absorbed by water and eye tissue; this wavelength causes corneal and vitreous injury: strict laser safety protocols and appropriate eye protection are mandatory.
- Fire hazard: Holmium metal powder is flammable; metal fires require Class D extinguishing agents.
- General toxicity: Holmium is considered to have low acute systemic toxicity; the primary hazards are physical (dust/fire, laser) rather than chemical toxicity.
Holmium in the Real World
Real-World Uses
- Ho:YAG surgical laser: The holmium:YAG laser (2100 nm infrared) is used in urology to fragment kidney stones (holmium laser lithotripsy), treat benign prostatic hyperplasia (HoLEP), and in arthroscopy to ablate cartilage and soft tissue with minimal bleeding.
- High-field magnetic pole pieces: Holmium has the highest magnetic moment of any element; holmium pole pieces are used in specialised laboratory electromagnets to concentrate and shape magnetic fields to the highest possible local values.
- Nuclear reactor neutron absorption: Holmium-165, the only stable holmium isotope, has a significant thermal neutron absorption cross-section; Ho₂O₃ pellets are studied as burnable absorbers and shielding material in compact research reactors.
- Optical fibre amplifiers: Holmium-doped fluoride fibre amplifiers emit in the 2 μm wavelength region, useful for atmospheric sensing, medical tissue surgery, and coherent LIDAR applications.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is holmium used for?
Holmium lasers (Ho:YAG, holmium-doped yttrium aluminium garnet) are widely used in medicine for urological surgery: particularly for fragmenting kidney stones (lithotripsy) and treating benign prostatic hyperplasia. Holmium has the highest magnetic moment of any naturally occurring element, making it useful in high-field electromagnets and as a pole piece in specialised MRI magnets. Holmium oxide colours glass yellow.
Is holmium the most magnetic element?
Holmium has the highest magnetic moment of any element: its magnetic moment is about 10.6 Bohr magnetons per atom. This arises from its 10 unpaired 4f electrons. However, holmium is not ferromagnetic at room temperature; it only becomes magnetically ordered at cryogenic temperatures (below about 19 K). Its extreme paramagnetism at low temperatures is exploited in specialised scientific magnets.
How was holmium discovered?
Holmium was discovered independently in 1878 by Swiss chemists Jacques-Louis Soret and Marc Delafontaine (spectroscopically) and by Swedish chemist Per Teodor Cleve (chemically). Cleve separated it from erbium oxide and named it holmium after Holmia, the Latin name for Stockholm, his home city.
How does a holmium laser break kidney stones?
The Ho:YAG laser emits infrared light at 2.1 micrometres, which is strongly absorbed by water. When the laser fibre is brought close to a kidney stone via a ureteroscope, the laser pulses create a small steam bubble at the stone surface. The rapid collapse of this bubble generates a shockwave that fragments the stone: a process called cavitation-assisted fragmentation. Holmium lasers can dust kidney stones into fine particles the body can pass naturally, avoiding open surgery.