Samarium (Sm)

Stable isotopes of samarium available from ISOFLEX

Isotope Z(p) N(n) Atomic Mass Natural Abundance Enrichment Level Chemical Form
Sm-144 62 82 143.911996 3.10% 88.00-93.00% Oxide
Sm-147 62 85 146.914894 15.0% 94.00-96.50% Oxide
Sm-148 62 86 147.914818 11.30% 91.00-96.50% Oxide
Sm-149 62 87 148.917180 13.80% >94.00% Oxide
Sm-150 62 88 149.917272 7.40% >94.00% Oxide
Sm-152 62 90 151.919729 26.70% ≥98.40% Oxide
Sm-154 62 92 153.922206 22.70% >98.50% Oxide

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Samarium was discovered in 1879 by Paul-Émile Lecoq de Boisbaudran. It is named for the mineral samarskite, from which Lecoq de Boisbaudran isolated the new element. The mineral in turn takes its name from Vasili Samarsky-Bykhovets, the one-time chief of staff of the Russian Corps of Mining Engineers.

Samarium is a hard, brittle, yellow metal, which quickly develops an oxide film in air. Its hardness is similar to that of iron. It exhibits two crystal forms: an alpha form, with a rhombohedral crystal structure at ordinary temperatures, changes to the body-centered cubic form at 917 ºC. The densities of the two forms are 7.52 g/cm3 and 7.40 g/cm3, respectively. Samarium is insoluble in water and soluble in acid. It is stable in dry air at ordinary temperatures; however, it oxidizes in moist air, forming an oxide coating. The metal ignites in air at about 150 ºC. It is an active reducing agent (it reduces several metal oxides to metals), and it liberates hydrogen from water. Among samarium's trivalent salts, the sesquioxide is commercially important, and the divalent compounds are primarily halides. The trivalent salts of these halogens are more stable than their divalent counterparts.

Samarium salts are used in optical glass, capacitors, thermoionic generating devices and sensitizers of phosphors. The metal is doped with calcium fluoride crystals for use in lasers. It is also used with other rare earths for carbon-arc lighting. Its alloys are used in permanent magnets.

Properties of Samarium

Name Samarium
Symbol Sm
Atomic number 62
Atomic weight 150.36
Standard state Solid at 298 °K
CAS Registry ID 7440-19-9
Group in periodic table N/A
Group name Lanthanoid
Period in periodic table 6 (Lanthanoid)
Block in periodic table f-block
Color Silvery white
Classification Metallic
Melting point 1074 °C
Boiling point 1791 °C
Vaporization point 1791 °C
Thermal conductivity 13.3 W/(m·K) at 298.2 °K
Electrical resistivity 94.0 µΩ·cm at 25 °C
Electronegativity 1.2
Specific heat 0.180 J/g mol at 20 °C
Heat of vaporization 175 kJ·mol-1 at 1791 °C
Heat of fusion 8.9 kJ·mol-1
Density of liquid 7.16 g/cm3 at 1074 °C
Density of solid 7.52 g/cm3
Electron configuration [Xe]4f66s2
Atomic radius 1.804 Å
Ionic radius Sm3+: 1.08 Å (coordination number 8)
Oxidation states +2, +3

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