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

Property	Value
Symbol	Ho
Atomic number	67
Atomic weight (mass)	164.9 g.mol-1
Group (number)	6 (Lanthanides)
Period	6
Color	A lustrous and bright silvery metal
Physical state	Solid at room temperature
Half-life	From 6(3) milliseconds to 4,570 years
Electronegativity according to Pauling	1.2
Density	8.8 g.cm-3 at 20°C
Melting point	1472°C, 2682°F, 1745 K
Boiling point	2700°C, 4892°F, 2973 K
Van der Waals radius	Unknown
Ionic radius	Unknown
Isotopes	36
Most characteristic isotope	165Ho
Electronic shell	[Xe] 4f116s2
The energy of the first ionization	580 kJ.mol-1
The energy of the second ionization	1136.6 kJ.mol-1
Discovery date	In 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. 

Nuclide [n 1]	Z	N	Isotopic mass (Da) [n 2][n 3]	Half-life [n 4]	Decay mode [n 5]	Daughter isotope [n 6]	Spin and parity [n 7][n 4]	Natural abundance (mole fraction)
	Excitation energy[n 4]							Normal proportion	Range of variation
140Ho	67	73	139.96854(54)#	6(3) ms			8+#
141Ho	67	74	140.96310(54)#	4.1(3) ms			(7/2−)
142Ho	67	75	141.95977(54)#	400(100) ms	β+	142Dy	(6 to 9)
					p	141Dy
143Ho	67	76	142.95461(43)#	300# ms [>200 ns]	β+	143Dy	11/2−#
144Ho	67	77	143.95148(32)#	0.7(1) s	β+	144Dy
					β+, p	143Tb
145Ho	67	78	144.94720(32)#	2.4(1) s	β+	145Dy	(11/2−)
146Ho	67	79	145.94464(21)#	3.6(3) s	β+	146Dy	(10+)
					β+, p (rare)	145Tb
147Ho	67	80	146.94006(3)	5.8(4) s	β+	147Dy	(11/2−)
					β+, p (rare)	146Tb
148Ho	67	81	147.93772(14)	2.2(11) s	β+	148Dy	(1+)
149Ho	67	82	148.933775(20)	21.1(2) s	β+	149Dy	(11/2−)
150Ho	67	83	149.933496(15)	76.8(18) s	β+	150Dy	2−
151Ho	67	84	150.931688(13)	35.2(1) s	β+ (78%)	151Dy	11/2(−)
					α (22%)	147Tb
152Ho	67	85	151.931714(15)	161.8(3) s	β+ (88%)	152Dy	2−
					α (12%)	148Tb
153Ho	67	86	152.930199(6)	2.01(3) min	β+ (99.94%)	153Dy	11/2−
					α (.05%)	149Tb
154Ho	67	87	153.930602(9)	11.76(19) min	β+ (99.98%)	154Dy	2−
					α (.02%)	150Tb
155Ho	67	88	154.929103(19)	48(1) min	β+	155Dy	5/2+
156Ho	67	89	155.92984(5)	56(1) min	β+	156Dy	4−
157Ho	67	90	156.928256(26)	12.6(2) min	β+	157Dy	7/2−
158Ho	67	91	157.928941(29)	11.3(4) min	β+ (93%)	158Dy	5+
					α (7%)	154Tb
159Ho	67	92	158.927712(4)	33.05(11) min	β+	159Dy	7/2−
160Ho	67	93	159.928729(16)	25.6(3) min	β+	160Dy	5+
161Ho	67	94	160.927855(3)	2.48(5) h	EC	161Dy	7/2−
162Ho	67	95	161.929096(4)	15.0(10) min	β+	162Dy	1+
163Ho	67	96	162.9287339(27)	4570(25) y	EC	163Dy	7/2−
164Ho	67	97	163.9302335(30)	29(1) min	EC (60%)	164Dy	1+
					β− (40%)	164Er
165Ho	67	98	164.9303221(27)	Observationally Stable[n 8]			7/2−	1.0000
166Ho	67	99	165.9322842(27)	26.83(2) h	β−	166Er	0−
167Ho	67	100	166.933133(6)	3.003(18) h	β−	167Er	7/2−
168Ho	67	101	167.93552(3)	2.99(7) min	β−	168Er	3+
169Ho	67	102	168.936872(22)	4.72(10) min	β−	169Er	7/2−
170Ho	67	103	169.93962(5)	2.76(5) min	β−	170Er	6+#
171Ho	67	104	170.94147(64)	53(2) s	β−	171Er	7/2−#
172Ho	67	105	171.94482(43)#	25(3) s	β−	172Er
173Ho	67	106	172.94729(43)#	10# s	β−	173Er	7/2−#
174Ho	67	107	173.95115(54)#	8# s
175Ho	67	108	174.95405(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.