Science Fair Project Encyclopedia
|Name, Symbol, Number||Samarium, Sm, 62|
|Group, Period, Block||_ , 6, f|
|Density, Hardness||7353 kg/m3, no data|
|Appearance|| silvery white|
|Atomic weight||150.36(3) amu|
|Atomic radius (calc.)||185 (238) pm|
|Covalent radius||no data|
|van der Waals radius||no data|
|e- 's per energy level||2, 8, 18, 24, 8, 2|
|Oxidation states (Oxide)||3 (mildly basic)|
|State of matter||solid (__)|
|Melting point||1345 K (1962 °F)|
|Boiling point||2076 K (3277 °F)|
|Molar volume||19.98 ×10-6 m3/mol|
|Heat of vaporization||166.4 kJ/mol|
|Heat of fusion||8.63 kJ/mol|
|Vapor pressure||563 Pa at 1345 K|
|Velocity of sound||2130 m/s at 293.15 K|
|Electronegativity||1.17 (Pauling scale)|
|Specific heat capacity||200 J/(kg*K)|
|Electrical conductivity||0.956 106/m ohm|
|Thermal conductivity||13.3 W/(m*K)|
|1st ionization potential||544.5 kJ/mol|
|2nd ionization potential||1070 kJ/mol|
|3rd ionization potential||2260 kJ/mol|
|4th ionization potential||3990 kJ/mol|
|Most stable isotopes|
|SI units & STP are used except where noted.|
Samarium is a rare earth metal, with a bright silver lustre, that is reasonably stable in air; it ignites in air at 150°C. Three crystal modifications of the metal also exist, with transformations at 734 and 922°C, respectively.
Uses of Samarium include:
- Carbon-arc lighting for the motion picture industry (together with other rare earth metals).
- Doping CaF2 crystals for use in optical masers or lasers.
- As a neutron absorber in nuclear reactors.
- For alloys and headphones.
- Samarium-Cobalt magnets; SmCo5 is used in making a new permanent magnet material with the highest resistance to demagnetization of any known material, and an intrinsic coercive force as high as 2200 kA/m.
- Samarium oxide is used in optical glass to absorb infrared light.
- Samarium compounds act as sensitizers for phosphors excited in the infrared.
- Samarium oxide is a catalyst for the dehydration and dehydrogenation of ethanol.
Samarium was first discovered spectroscopically in 1853 by Swiss chemist Jean Charles Galissard de Marignac by its sharp absorption lines in didymium, and isolated in Paris in 1879 by French chemist Paul Émile Lecoq de Boisbaudran from the mineral samarskite ((Y,Ce,U,Fe)3(Nb,Ta,Ti)5O16). Like the mineral, it was named after a Russian mine official, Colonel Samarski .
Samarium has no known biological role, but is said to stimulate the metabolism.
Samarium is never found free in nature, but, like other rare earth elements, is contained in many minerals, including monazite, bastnasite and samarskite; monazite (in which it occurs up to an extent of 2.8%) and bastnasite are also used as commercial sources. Misch metal containing about 1% of samarium has long been used, but it was not until recent years that relatively pure samarium has been isolated through ion exchange processes, solvent extraction techniques, and electrochemical deposition . The metal is often prepared by electrolysis of a molten mixture of samarium(III) chloride with sodium chloride or calcium chloride. Samarium can also be obtained by reducing its oxide with lanthanum.
Compounds of Samarium include:
Naturally occurring samarium is composed of 4 stable isotopes, 144-Sm, 150-Sm, 152-Sm and 154-Sm, and 3 radioisotopes, 147-Sm, 148-Sm and 149-Sm, with 152-Sm being the most abundant (26.75% natural abundance). 32 radioisotopes have been characterized, with the most stable being 148-Sm with a half-life of 7E+15 years, 149-Sm with a half-life of more than 2E+15 years, and 147-Sm with a half-life of 1.06E+11 years. All of the remaining radioactive isotopes have half-lifes that are less than 1.04E+8 years, and the majority of these have half lifes that are less than 48 seconds. This element also has 5 meta states with the most stable being 141m-Sm (t½ 22.6 minutes), 143m1-Sm (t½ 66 seconds) and 139m-Sm (t½ 10.7 seconds).
The primary decay mode before the most abundant stable isotope, 152-Sm, is electron capture, and the primary mode after is beta minus decay. The primary decay products before 152-Sm are element Pm (promethium) isotopes, and the primary products after are element Eu (europium) isotopes.
As with the other lanthanides, samarium compounds are of low to moderate toxicity, although their toxicity has not been investigated in detail.
- N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, Pergamon Press, Oxford, UK, 1984.
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