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Samarium

What is samarium?

Samarium is a chemical element or rare earth metal in the periodic table with the symbol Sm and atomic number 62. It is a soft, ductile, and silvery-white rare earth metal that lies with f-block elements or lanthanides. The density and hardness of samarium are similar to that of zinc.

Samarium element or rare earth metal symbol Sm, uses, properties, and facts

Like neodymium, it is alloyed with cobalt to form samarium-cobalt magnets. It is also used in X-ray lasers, glasses, a catalyst for alcohol production, nuclear medicine, and an absorber in nuclear power reactors.

The radioactive isotope samarium-153 is an active component of radioactive medicine. In medicinal chemistry, Sm-153 is used for the treatment of lung cancer, prostate cancer, breast cancer, and osteosarcoma.

Another isotope, samarium-149 is a strong neutron absorber. Therefore, it is added to the control rods of nuclear power reactors.

Where is samarium found?

It is the 40th most abundant element in earth’s crust and the 5th most abundant element among the lanthanides family. Samarium is found along with other rare earth metals in various minerals. The principal minerals of Sm are monazite and bastnaesite.

The most abundant commercial source of samarium is China, India, Brazil, the US, Australia, and Sri Lanka.

It can be separated from the other rare earth metals by ion exchange chromatography and solvent extraction method. Recently, the electrochemical deposition technique has been used to separate samarium from other lanthanides.

Isotopes

Naturally occurring rare earth metal samarium contains five stable isotopes with mass numbers 144, 149, 150, 152, and 154. Artificial nuclear reactions may be synthesized various radioactive isotopes of Sm. Some isotopes are obtained by the radioactive decay of neodymium isotopes.

It contains two extremely long-lived radioactive isotopes 147Sm (half-life t1/2 = 1.06×1011 years) and 148Sm (7×1015 years). These two isotopes are obtained primarily by alpha decay to neodymium. Lighter unstable isotopes are obtained by electron capture to promethium.

The radioactive isotope, Sm-153 is used to kill cancer cells in the lungs, prostate, breast, and osteosarcoma. Another isotope, Sm-149 is used as a strong neutron absorber in control rods of nuclear reactors.

Properties

Samarium is a silvery white rare earth metal belonging to the lanthanide family of the periodic table. It is relatively stable at room temperature but ignites when heated at 150 °C. It forms an oxide layer in moist air.

Like rare earth metal europium, samarium has also shown a stable +2 oxidation state along with a +3 state.

Samarium
Symbol Sm
Discovery Paul-Émile Lecoq de Boisbaudran in 1879
Name derived from The mineral samarskite which was used for the first isolation
Common isotope 62Sm152
Oxidation states +3, +2
CAS number 7440-19-9
Periodic properties
Atomic number 62
Relative atomic mass 150.36
Electron per cell 2, 8, 18, 24, 8, 2
Electronic Configuration [Xe] 4f6 6s2
Block f-block
Group Lanthanides
Period 6
Physical properties
State at 20 °C Solid
Melting point 1072 °C, 1345 K
Boiling point 1794°C, 2067 K
Molar heat capacity 29.54 J mol−1 K1
Crystal structure ​rhombohedral
Density 7.52 g/cm3
Heat of fusion 8.62 kJ mol−1
Heat of vaporization 192 kJ mol−1
Atomic properties
Atomic radius (non-bonded) 2.36 Å
Covalent radius 1.85 Å
Electronegativity 1.17 (Pauling scale)
Electron affinity Unknown
Ionization energy (kJ/mol) 1st 2nd 3rd
544.53 1068.09 2257.80

Electron configuration

Samarium atomic structure and electron per shell with atomic number, atomic mass, electronic configuration and energy levels

The 62 electrons of the samarium are arranged to show the electron configuration of [Xe] 4f6 6s2. Like europium, Sm commonly uses two or three valence electrons to show +2 or +3 oxidation numbers or states.

Samarium in the periodic table

It is placed with lanthanide in the periodic table. Samarium is a costly rare earth metal that lies between promethium and europium.

Samarium element (lanthanide or rare earth metal) symbol Sm and position in the periodic table with atomic number, electronic configuration

Chemical properties

Samarium is a highly electropositive and active metal. The electrode potential value of Sm is comparable to that of alkaline earth metals. It acts as a strong reducing agent.

The compact rare earth metal is quite stable to dry air at ordinary temperatures but rapidly dull in a humid atmosphere. Samarium metal tarnishes slowly in the air by forming an oxide layer.

Like other rare earth metals, it also burns in oxygen at 150 °C to form Sm (III) oxide.
4 Sm + 3 O2 → 2 Sm2O3

Samarium is attacked by acids like dilute sulfuric acid with the liberation of hydrogen gas. The acidic solutions contain pale green Sm3+ ions.
2 Sm + 3 H2SO4 + 16 H2O → 2 [Sm(H2O)9]+3 + 3 SO4−2 + 3 H2

Facts about samarium

  • The most common oxidation state of samarium is +3 but like europium +2 state is also common.
  • Samarium is the hardest and the most brittle of the rare earth elements that tarnish in air and ignite in oxygen at 150 °C to form Sm oxide.
  • Under ordinary conditions, the metal has rhombohedral crystals but after heating changes the crystal structure to hexagonal close-packed (hcp). Further heating, Sm formed a body-centered cubic (bcc) phase.
  • It is used to make samarium-cobalt permanent magnets, samarium X-ray lasers, glasses, a catalyst for alcohol production, pain treatment medicine for bone cancer, and an absorber in nuclear reactors.
  • It is a costly rare earth metal. An approximate price of pure samarium is about $360 per 100 grams of Sm metal.
  • It may be separated from minerals monazite and bastnasite using ion exchange chromatography and solvent extraction methods. Electrolysis may also be used for the production of pure samarium metal from its molten chloride with sodium chloride.
  • The low toxic samarium metal has no known biological role.

Chemical compounds

It is one of the few lanthanides that shows an oxidation state of +2 along with a +3 state. The aqueous solution Sm2+ ions show blood-red colour.

Samarium oxides

The most common and stable oxide of Sm is Sm2O3. Samarium metal also formed monoxide with the chemical formula SmO. The metal tarnishes readily in the humid air by forming an Sm (III) oxide layer.

The oxide is obtained by burning the metal in air or oxygen at a temperature above 150 °C.
4 Sm + 3 O2 → 2 Sm2O3

It is also obtained by thermal decomposition of samarium (III) carbonate, hydroxide, nitrate, oxalate, or sulfate.

Sm2O3 is commonly white to off-yellow in colour that used in optical and infrared absorbing glass to absorb infrared radiation. It is also used as a neutron absorber in control rods of nuclear power reactors.

Samarium hydroxide

It is an important chemical compound of samarium with the chemical formula Sm(OH)3. It forms samarium (III) salts when react with sulfuric acid.
2 Sm(OH)3 + 6 H2SO4 → Sm2(SO4)3 + 6 H2O

It is potentially used in electronics, optics, and catalysis.

Halides

The metal Sm reacts with all the halogens like fluorine, chlorine, bromine, and iodine to form trihalides.

2 Sm + 3 X2→ 2 SmX3 (X = F, Cl, Br or I)

The dihalides are obtained by further reduction of trihalides with samarium, lithium, or sodium at elevated temperatures (about 700–900 °C). In addition to dihalides, the reduction also produces various non-stoichiometric halides like Sm3F7, Sm14F33, Sm27F64, Sm11Br24, Sm5Br11, and Sm6Br13.

Uses of samarium

It is used widely for making samarium-cobalt magnets. It may also be used in various catalysis processes, absorbers in nuclear reactors, medicine for cancer treatment, making glasses, etc.

Samarium-cobalt magnets

It is used for making samarium-cobalt magnets with the chemical formula SmCo5 or Sm2Co17. Such types of magnets are much more powerful than iron magnets.

Samarium-cobalt magnets are used commonly in small motors, headphones, and high-end magnetic pickups for guitars and related musical instruments. Presently, due to the high price of Sm, these magnets are replaced by neodymium magnets.

It is suitable only for high-temperature applications. They show magnetic properties at high temperatures. Therefore, these magnets are used in microwaves.

In catalysis

Samarium and its compounds are very useful in catalysis processes.

  • These catalysts help to decompose pollution products such as plastics and polychlorinated biphenyls (PCB).
  • They are also useful for dehydration and dehydrogenation of ethanol.
  • Sm (III) triflate is an effective Lewis acid catalyst that is used in halogen-promoted Friedel–Crafts reaction with alkenes.
  • Sm (II) iodide is a very common reducing and coupling agent that uses for the synthesis of various organic compounds.

In medicine

The beta emitter samarium-153 (half-life 46.3 hours) is used to kill cancer cells in lung cancer, prostate, breast, and osteosarcoma.

In quadramet medication, Sm-153 is chelated with ethylene diamine tetramethylene phosphonate (EDTMP) and injected intravenously. The chelation prevents the accumulation of radioactive samarium in our body but beta radiation can kill cancer cells of lung cancer, prostate cancer, breast cancer, and osteosarcoma.

In nuclear reactors

Samarium-149 has a high cross-section for neutron capture. Therefore, it is used in control rods of nuclear reactors due to the stability of absorption compared to other materials such as boron and cadmium. Most of the nuclear fusion and decay products of 149Sm are other isotopes of samarium and are also good neutron absorbers.

Other applications

  • It is used for making carbon arc lamp electrodes for studio lighting and projection.
  • The off-yellow colour Sm2O3 is used in optical and infrared absorbing glass to absorb infrared radiation.
  • A minor quantity of Sm is a part of mischmetal that is used in the ignition devices of many lighters and torches.
  • Samarium-doped crystalline solids like calcium chloride or calcium are used for making optical lasers.