Atomic number 62

Samarium

Sm
+ phase
− phase

Shells Orbitals 4f 6s

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62 electrons in 6 shells: 2, 8, 18, 24, 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: 150.36(2) Da
Electron configuration: [Xe] 4f⁶ 6s²
Phase at 25 °C: solid
Melting point: 1072 °C
Boiling point: 1900 °C
Density: 7.52 g/cm³
Electronegativity (Pauling): 1.17
Discovered: 1879, Paul-Émile Lecoq de Boisbaudran

Neighbours in the table

Pm Eu

Colonel Samarski, a Russian mine official, gave his name to a mineral, and the mineral gave it to element 62. That mineral is samarskite, in the history by CIAAW, the atomic-weights commission of IUPAC (the International Union of Pure and Applied Chemistry). Lecoq de Boisbaudran detected the element in samarskite in 1879 by its sharp absorption lines, Los Alamos records.

Rival claims surround 1879. The Swiss chemist Jean Charles Galissard de Marignac saw its spectrum in a material known as didymia in 1853, Jefferson Lab reports. By Jefferson Lab’s account, Boisbaudran was the first to isolate it, in 1879. In CIAAW’s account, Marc Delafontaine found it in 1878 and named it decipium. In 1881 he showed that decipium held two elements, one of them Boisbaudran’s samarium. In 1901 Eugène-Anatole Demarçay showed that Boisbaudran’s samarium also held europium, CIAAW adds.

For samarium, shells of 2, 8, 18, 24, 8 and 2 hold 62 electrons: [Xe] 4f⁶ 6s². Its oxidation states are +3 and +2 in Jefferson Lab’s list, and 4, 3, 2 and 1 in Los Alamos’s. An oxidation state is the charge an atom would hold if all its bonds were ionic. The metal has a bright silver lustre and is reasonably stable in air, Los Alamos notes; its crystal packing changes twice on heating, at 734 and 922 °C.

Where it is found

Each kilogram of the Earth’s crust holds 7.05 milligrams of samarium, and seawater 4.5 × 10⁻⁷ milligrams per litre, in Jefferson Lab’s figures. Monazite and bastnasite are its commercial sources, Los Alamos reports, and monazite runs to 2.8 per cent samarium. Samarskite, the mineral of its discovery, is an oxide of niobium, tantalum and titanium that also carries yttrium, cerium, uranium and iron, by Jefferson Lab’s formula.

Natural samarium is a mixture of seven isotopes. In CIAAW’s figures, samarium-152 is the commonest at 26.74 per cent of atoms, then samarium-154 at 22.74 per cent and samarium-147 at 15.00 per cent. Samarium-147 and samarium-148 emit alpha particles, and samarium-149 possibly does as well, in the tables of the Atomic Mass Data Center (AMDC) of the International Atomic Energy Agency (IAEA).

Most samarium now comes from monazite sand through ion exchange, Jefferson Lab notes. The metal itself can be made by reducing the oxide with lanthanum, in Los Alamos’s account.

Why it matters

Paired with cobalt as SmCo₅, samarium makes a permanent magnet that resists demagnetisation, the loss of its magnetism, better than any other known material, Los Alamos and Jefferson Lab report. Samarium-cobalt alloy is among potential acquisitions for the US stockpile, in US Geological Survey figures: 200 tonnes in fiscal 2024 and 60 in fiscal 2025.

Samarium-147 is a clock for geologists. Its half-life is 1.073 × 10¹¹ years in the IAEA’s evaluation. The isotope dates igneous and metamorphic rocks through the minerals inside them, IUPAC reports. Read with hafnium, tungsten and neodymium results, samarium isotopes suggest the Moon’s magma formed about 70 million years after the Solar System’s birth. It had crystallised by about 215 million years.

Samarium-153, a beta emitter with a half-life of 46.284 hours in the IAEA’s evaluation, is used to treat the severe pain of cancers that have reached the bones, IUPAC notes. Samarium also serves as a neutron absorber in reactors, Los Alamos reports, and lasers use crystals laced with samarium.

Samarium oxide absorbs infrared in optical glass, on Los Alamos’s page. The sulfide stays stable at high temperature and turns heat into electricity with good efficiency up to 1100 °C. Sm₂O₃ also speeds the removal of water and of hydrogen from ethanol, Jefferson Lab reports.

Properties

Properties of samarium 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	62
Standard atomic weight	150.36(2) Da	Da	IUPAC/CIAAW 2024
Melting point	1072 °C	°C	Los Alamos: 1072 °C
Boiling point	1900 °C	°C	Los Alamos: 1900 °C
Density	7.52 g/cm³	g/cm³
Electronegativity (Pauling)	1.17
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f⁶
Phase at 25 °C	solid

Safety

Samarium metal is a flammable solid, and the Globally Harmonized System (GHS) of hazard labels gives it the signal word Danger. Of the company reports to the European Chemicals Agency giving hazard codes, 91% class it as a flammable solid and 94.1% say it releases flammable gas with water. Heated in air to about 150 °C, the metal catches fire, Los Alamos notes, and little is known about its toxicity. Hazards and handling are set out in the PubChem Laboratory Chemical Safety Summary for samarium.

Questions

What else is samarium used for?

Samarium, along with other rare earths, has been used in carbon-arc lighting for studio lights and projectors in the motion picture industry, Los Alamos and Jefferson Lab report. Misch metal, the alloy in lighter flints, is about 1 per cent samarium, Jefferson Lab adds. Samarium oxide also goes into glass that absorbs infrared, and the metal serves as a neutron absorber in nuclear reactors, in Los Alamos's account.

Is samarium radioactive?

Two of natural samarium's isotopes are unstable, each with a long half-life, the time for half a sample to decay, in the Atomic Mass Data Center's tables. Samarium-147 emits alpha particles with a half-life of 1.073 × 10¹¹ years in the evaluation of the International Atomic Energy Agency (IAEA). Samarium-148 also alpha-decays, over 6.3 × 10¹⁵ years in the Atomic Mass Data Center's tables. Samarium-153, used in medicine, lasts 46.284 hours in the IAEA's evaluation.

What are samarium-cobalt magnets?

They are permanent magnets built on the compound SmCo₅, which Los Alamos and Jefferson Lab both describe as the known material most resistant to demagnetisation. Samarium-cobalt alloy appears in US stockpile acquisition plans for fiscal 2024 and 2025, the US Geological Survey reports. For rare earths as a group, the US Geological Survey adds, significant amounts reach the United States as permanent magnets inside finished goods.

Can samarium metal catch fire?

It can. Samarium ignites in air at about 150 °C, according to Los Alamos and the Hazardous Substances Data Bank (HSDB). The powder is flammable when exposed to flame or to oxidisers, HSDB adds, and the metal reacts with water to release hydrogen, itself flammable.