Atomic number 67

Holmium

Ho
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Shells Orbitals 4f 6s

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67 electrons in 6 shells: 2, 8, 18, 29, 8, 2.

Shells are a teaching model: an electron does not travel on a ring at a fixed distance.

Category: Lanthanide
Period: 6
Block: f
Standard atomic weight: 164.93(1) Da
Electron configuration: [Xe] 4f¹¹ 6s²
Phase at 25 °C: solid
Melting point: 1461 °C
Boiling point: 2600 °C
Density: 8.80 g/cm³
Electronegativity (Pauling): 1.23
Discovered: 1878, Delafontaine and Soret

Neighbours in the table

Dy Er

Stockholm’s Latin name, Holmia, became holmium, after the native city of the Swedish chemist Per Theodor Cleve, in Los Alamos’s history. Homberg proposed the name, in the history by CIAAW, the atomic-weights commission of IUPAC (the International Union of Pure and Applied Chemistry). His motive was to recognise Cleve, or perhaps to secure his own place in history.

In 1878 the Swiss chemists Delafontaine and Soret noticed its special absorption bands and announced an “Element X”, Los Alamos reports. Their sighting falls earlier in 1879 in Jefferson Lab’s account. Cleve found the element independently in 1879 by stripping every known contaminant from erbia, the oxide of erbium. Two new materials remained: a green one he named thulia and a brown one he named holmia, holmium’s oxide.

Across its shells, holmium arranges 67 electrons as 2, 8, 18, 29, 8 and 2. Eleven sit in the 4f subshell, a group of orbitals within the fourth shell, and two in 6s: [Xe] 4f¹¹ 6s². The pure metal has a metallic to bright silver lustre and is relatively soft and malleable, according to Los Alamos. Its atoms pack in a hexagonal close-packed crystal, where each atom has 12 nearest neighbours, in Chem1’s description of that structure. Dry air at room temperature leaves the metal alone, but moist air and heat oxidise it rapidly.

Where it is found

Each kilogram of the Earth’s crust holds an estimated 1.3 milligrams of holmium, and a litre of seawater about 2.2 × 10⁻⁷ milligrams, on Jefferson Lab’s figures. Holmium occurs in gadolinite, monazite and other rare-earth minerals, Los Alamos reports. Monazite is its commercial source, carrying about 0.05 per cent holmium.

Today ion exchange separates the element from monazite sand, according to Jefferson Lab. World mine output of all rare earths reached an estimated 390,000 tons of oxide equivalent in 2024, 270,000 of them from China, in US Geological Survey figures. The United States mined 45,000 tons of that total, and Burma 31,000.

Homberg first isolated it in 1911, in CIAAW’s history, and prepared holmia that year as a yellow oxide, in Los Alamos’s account. The metal has been obtained by reducing its anhydrous, or water-free, chloride or fluoride with calcium, Los Alamos notes.

Why it matters

Few uses have yet been found for holmium, Los Alamos reports, and in Jefferson Lab’s account the metal has no commercial applications and forms no commercially important compounds. Its unusual magnetic properties could be exploited in future, Jefferson Lab suggests.

All natural holmium is one stable isotope, holmium-165. Holmium-166 decays entirely by beta-minus emission, in which the nucleus gives out an electron. Its half-life is 26.824 hours in the evaluation of the International Atomic Energy Agency (IAEA). Being paramagnetic, weakly drawn into a magnetic field, and giving off beta and gamma rays together makes the isotope ideal for radioembolisation, in IUPAC’s notes.

In that treatment, radioactive particles travel through the bloodstream to a tumour. Holmium-166 microspheres have treated liver metastases, tumours spread from elsewhere, this way. The same properties let magnetic resonance imaging and SPECT, single-photon emission computed tomography, show where the spheres went.

Other holmium-166 agents treat arthritis by radiosynovectomy, radiation given inside the affected joint. One form, holmium-166 ferric hydroxide macroaggregate (FHMA), is used because it minimises leakage of the isotope outside the joint, IUPAC notes. A holmium-166 skin patch irradiates superficial skin cancers and Bowen’s disease from outside the body. A complex of the isotope with chitosan, a long-chain sugar like cellulose, serves in liver cancer therapy.

Properties

Properties of holmium Standard atomic weights from IUPAC/CIAAW (abridged, 2024); other values from PubChem's periodic table, kelvin converted to °C.
Property	Value	Unit	Source
Atomic number	67
Standard atomic weight	164.93(1) Da	Da	IUPAC/CIAAW 2024
Melting point	1461 °C	°C	Los Alamos: 1461 °C
Boiling point	2600 °C	°C	Los Alamos: 2600 °C
Density	8.80 g/cm³	g/cm³
Electronegativity (Pauling)	1.23
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹¹
Phase at 25 °C	solid

Safety

Holmium metal is a flammable solid in 84% of 50 company reports to the European Chemicals Agency, with the signal word Danger. Another 8%, 4 of 50 reports, find that it meets no hazard criteria of the Globally Harmonized System (GHS). Its acute toxicity is rated low by Haz-Map and on Los Alamos’s page. The PubChem Laboratory Chemical Safety Summary for holmium gives the classification and handling guidance.

Questions

Who discovered holmium?

Two Swiss chemists, Delafontaine and Soret, spotted its absorption bands in 1878 and announced an Element X, according to Los Alamos. The Swedish chemist Per Theodor Cleve found it on his own in 1879 in erbia, the oxide of erbium, on the dates given by CIAAW and Jefferson Lab. Holmium itself was first isolated in 1911, by Homberg, in CIAAW's history on PubChem's record.

Why is holmium called holmium?

Holmia is the Latin word for Stockholm, and the element honours the city where Cleve was born, Los Alamos reports. Homberg proposed the name, in the history by CIAAW, IUPAC's atomic-weights commission, with two possible motives: to honour Cleve, a Stockholm man, or to make Homberg's own name last. Cleve had already called the brown oxide he separated holmia, in Jefferson Lab's account.

What is holmium used for?

Holmium metal has no commercial applications in Jefferson Lab's account, and few uses for it have been found, Los Alamos reports. Medicine uses one of its radioactive isotopes instead. Holmium-166 goes into microspheres for liver metastases, into agents for arthritis and for pain from bone metastases, into a skin patch for superficial skin cancers, and into labelled antibodies for radioimmunotherapy, in IUPAC's isotope notes.

Is holmium radioactive?

Natural holmium is not: all of it is the stable isotope holmium-165, with an abundance of 1 in CIAAW's isotope table. Holmium-166 is radioactive and decays entirely by beta-minus emission, with a half-life of about a day. It gives off gamma rays as well as beta particles, IUPAC adds. The isotope was discovered in 1936, in the International Atomic Energy Agency's nuclear data.