Holmium (Ho)

Holmium is a chemical element with an atomic number of 67 in the periodic table. It’s not found in the Earth’s crust. Classified as a member of the lanthanide series of elements, this rare-earth metal is a divalent substance with a +3 oxidation state, strong magnetic properties, and astounding stability of its electron shell. 

Chemical and Physical Properties of Holmium

Atomic number67
Atomic weight (mass)164.9 g.mol-1
Group (number)6 (Lanthanides)
ColorA lustrous and bright silvery metal
Physical stateSolid at room temperature
Half-lifeFrom 6(3) milliseconds to 4,570 years
Electronegativity according to Pauling1.2
Density8.8 g.cm-3 at 20°C
Melting point1472°C, 2682°F, 1745 K
Boiling point2700°C, 4892°F, 2973 K
Van der Waals radiusUnknown
Ionic radiusUnknown
Most characteristic isotope165Ho
Electronic shell[Xe] 4f116s2
The energy of the first ionization580 kJ.mol-1
The energy of the second ionization1136.6 kJ.mol-1
Discovery dateIn 1878 by J.L. Soret

Holmium is a rare-earth element with the periodic table symbol (Ho), atomic number 67, atomic mass of 164.9 g.mol-1, and electron configuration [Xe] 4f116s2. It comprises a lanthanoid atom and an f-block element atom. This chemical element is a soft, malleable, and lustrous metal with strong magnetic properties. It reaches its boiling point at 2700°C (4892°F, 2973 K), while the melting point is achieved at 2700°C (4892°F, 2973 K). 

A member of the lanthanide family of elements in the periodic table, holmium has an electronegativity of 1.2 according to Pauling, whereas the atomic radius according to van der Waals is unknown.  

This lanthanide is a highly reactive substance. In the form of a solution, holmium (Ho 3+) is surrounded by nine H2O molecules. Furthermore, it easily reacts with acids that dissolve this chemical and adopts the oxidation state of +3.

How Was Holmium Discovered?

In 1978, two parallel stories on the discovery of holmium emerged.

The Discovery of the Swiss Team of Spectroscopists

Upon conducting their chemical trials by using the spectroscopy method at the University of Geneva, the Swiss chemists and spectroscopists Marc Delafontaine (1837 – 1911) and Jacques-Louis Soret (1827 – 1890) detected new lines in the spectra of the yttrium sample.

Prior to this, they had already isolated the element erbium from which they intended to extract ytterbium. Learning the fact that yttrium contains traces of other rare-earth elements, the team of Delafontaine and Soret introduced the new element ‘X’ to the world, later named as holmium (Ho). 

The Contribution of the Swedish Team of Chemists

At the same time, in 1978, a team of scientists at Uppsala, Sweden, was performing a more thorough analysis on what has been removed from ytterbium. Led by the Swedish chemist Per Teodor Cleve (1840 – 1905), the Swedish team came upon the same two new materials – the strange green and brown lines of the spectra the Swiss team had observed. Cleve applied the same method Carl Gustaf Mosander used to discover lanthanum, erbium, and terbium in his research conducted on erbia, i.e. erbium oxide sample.

The Swedish team labeled the brown chemical as ‘holmia’, while the green substance was named ‘thulia’. By conducting further analysis, the Swedish team of scientists determined that the first substance was, in fact, holmium oxide, while the second one was thulium oxide. 

In the end, it remains unclear whether any of the research teams succeeded in isolating the pure elemental form of holmium back in 1978 since the rare-earth element dysprosium was later extracted from holmium. 

How Did Holmium Get Its Name?

Holmium got its name after Holmia, the Latin name for Stockholm, Sweden.

Where Can You Find Holmium?

As is the case with all rare-earth metals, holmium does not occur naturally in its free elemental form. It’s mined from the minerals gadolinite, monazite, and bastnäsite. These mineral ores are the main sources of this soft metal silvery substance with a lustrous shine. 

Typically, the monazite and bastnaesite ores are first processed to extract yttrium, after which holmium is isolated via the ion-exchange process. In the laboratory, the pure holmium substance is obtained by reacting calcium metal with holmium fluoride (HoF3). 

The United States, China, Sri Lanka, Brazil, India, and Australia are the countries where the largest holmium ore mines are located. 

Holmium in Everyday Life

Being a rare-earth element, holmium has very limited use in everyday life. Its unusual magnetic properties make holmium most suitable in the following instances:

  • As an addition in alloys that are further applied in the manufacturing of magnets. Also, this lanthanide has found its use as a flux concentrator for high magnetic fields; 
  • Furthermore, holmium possesses a strong ability to absorb neutrons. Due to this chemical property, element 67 is used in nuclear reactors in order to keep the chain reaction under control; 
  • As a calibrator, Ho is the preferred chemical in the manufacturing process of optical spectrophotometers. Moreover, holmia or holmium(III) oxide (Ho2O3) gives yellow or red color to cubic zirconia or glass; 
  • Finally, the radioactive isotopes of holmium have a significant application in the solid-state lasers used for vaporizing tumorous tissues during non-invasive medical procedures for the treatment of cancer and kidney stones. 

How Dangerous Is Holmium?

Holmium is considered to be of low toxicity. Since this element is found in minuscule traces in the human body, it’s considered to have a stimulating effect on the metabolic processes in the body by affecting the mechanisms of some bacteria. However, these claims are yet to be thoroughly studied. 

Environmental Effects of Holmium

There are no known hazards imposed by the presence of the elemental form of holmium in the environment. 

Isotopes of Holmium

There are 36 forms of holmium. The isolated holmium isotopes have atomic masses that range from 140Ho to 175Ho. However, the pure elemental form of holmium is made up of only one form of the element, i.e. the stable isotope 165Ho. 

Among the synthetic radioactive isotopes of holmium, holmium-163 is the most stable radioactive form of this rare earth element, with a half-life of 4570 years. 


[n 1]

ZNIsotopic mass (Da)

[n 2][n 3]


[n 4]



[n 5]



[n 6]

Spin and


[n 7][n 4]

Natural abundance (mole fraction)
Excitation energy[n 4]Normal proportionRange of variation
140Ho6773139.96854(54)#6(3) ms  8+#  
141Ho6774140.96310(54)#4.1(3) ms  (7/2−)  
142Ho6775141.95977(54)#400(100) msβ+142Dy(6 to 9)  
143Ho6776142.95461(43)#300# ms

[>200 ns]

144Ho6777143.95148(32)#0.7(1) sβ+144Dy   
β+, p143Tb
145Ho6778144.94720(32)#2.4(1) sβ+145Dy(11/2−)  
146Ho6779145.94464(21)#3.6(3) sβ+146Dy(10+)  
β+, p (rare)145Tb
147Ho6780146.94006(3)5.8(4) sβ+147Dy(11/2−)  
β+, p (rare)146Tb
148Ho6781147.93772(14)2.2(11) sβ+148Dy(1+)  
149Ho6782148.933775(20)21.1(2) sβ+149Dy(11/2−)  
150Ho6783149.933496(15)76.8(18) sβ+150Dy2−  
151Ho6784150.931688(13)35.2(1) sβ+ (78%)151Dy11/2(−)  
α (22%)147Tb
152Ho6785151.931714(15)161.8(3) sβ+ (88%)152Dy2−  
α (12%)148Tb
153Ho6786152.930199(6)2.01(3) minβ+ (99.94%)153Dy11/2−  
α (.05%)149Tb
154Ho6787153.930602(9)11.76(19) minβ+ (99.98%)154Dy2−  
α (.02%)150Tb
155Ho6788154.929103(19)48(1) minβ+155Dy5/2+  
156Ho6789155.92984(5)56(1) minβ+156Dy4−  
157Ho6790156.928256(26)12.6(2) minβ+157Dy7/2−  
158Ho6791157.928941(29)11.3(4) minβ+ (93%)158Dy5+  
α (7%)154Tb
159Ho6792158.927712(4)33.05(11) minβ+159Dy7/2−  
160Ho6793159.928729(16)25.6(3) minβ+160Dy5+  
161Ho6794160.927855(3)2.48(5) hEC161Dy7/2−  
162Ho6795161.929096(4)15.0(10) minβ+162Dy1+  
163Ho6796162.9287339(27)4570(25) yEC163Dy7/2−  
164Ho6797163.9302335(30)29(1) minEC (60%)164Dy1+  
β (40%)164Er
165Ho6798164.9303221(27)Observationally Stable[n 8]7/2−1.0000 
166Ho6799165.9322842(27)26.83(2) hβ166Er0−  
167Ho67100166.933133(6)3.003(18) hβ167Er7/2−  
168Ho67101167.93552(3)2.99(7) minβ168Er3+  
169Ho67102168.936872(22)4.72(10) minβ169Er7/2−  
170Ho67103169.93962(5)2.76(5) minβ170Er6+#  
171Ho67104170.94147(64)53(2) sβ171Er7/2−#  
172Ho67105171.94482(43)#25(3) sβ172Er   
173Ho67106172.94729(43)#10# sβ173Er7/2−#  
174Ho67107173.95115(54)#8# s     
175Ho67108174.95405(64)#5# s  7/2−#  

Source: Wikipedia

List of Holmium Compounds 

Holmium’s molecule is stable when exposed to dry air. Its most commonly occurring oxidation state is +3. When exposed to high temperatures or moist air, holmium oxidizes to a yellow oxide (Ho2O3). 

The most frequently occurring compounds of holmium are presented in the following list:

  • Holmium titanate
  • Holmium(III) bromide
  • Holmium chloride
  • Holmium(III) chloride
  • Holmium(III) fluoride
  • Holmium(III) oxide
  • Holmium silicide
  • Holmium iodide
  • Holmium nitride
  • Holmium vanadate

5 Interesting Facts and Explanations

  1. For a member of the lanthanide family of elements, holmium is pretty rare. It’s the 56th most abundant element in the Earth’s crust. However, despite being labeled as rare, holmium is 20 times more abundant than silver. 
  2. Holmium does not exist at all in the Earth’s atmosphere. 
  3. Among all of the naturally occurring elements, holmium possesses the highest magnetic moment (10.6 µB). 
  4. Most of the chemical compounds that contain holmium display brownish-yellow color. 
  5. Holmium(III) oxide (Ho2O3) is characterized with the strongest paramagnetic properties among all known chemical substances.