samarium

62 promethium ← samarium → europium - ↑ Sm ↓ Pu Periodic Table - Extended Periodic Table
General
Name, Symbol, Number	samarium, Sm, 62
Element category	lanthanides
Group, Period, Block	n/a, 6, f
Appearance	silvery white
Standard atomic weight	150.36(2)  g·mol−1
Electron configuration	[Xe] 6s2 4f6
Electrons per shell	2, 8, 18, 24, 8, 2
Physical properties
Phase	solid
Density (near r.t.)	7.52  g·cm−3
Liquid density at m.p.	7.16  g·cm−3
Melting point	1345 K (1072 °C, 1962 °F)
Boiling point	2067 K (1794 °C, 3261 °F)
Heat of fusion	8.62  kJ·mol−1
Heat of vaporization	165  kJ·mol−1
Specific heat capacity	(25 °C) 29.54  J·mol−1·K−1
Vapor pressure P(Pa) 1 10 100 1 k 10 k 100 k at T(K) 1001 1106 1240 (1421) (1675) (2061)
Atomic properties
Crystal structure	rhombohedral
Oxidation states	3, 2 (mildly basic oxide)
Electronegativity	1.17 (Pauling scale)
Ionization energies (more)	1st:  544.5  kJ·mol−1
	2nd:  1070  kJ·mol−1
	3rd:  2260  kJ·mol−1
Atomic radius	180  pm
Covalent radius	198±8  pm
Miscellaneous
Magnetic ordering	paramagnetic[1]
Electrical resistivity	(r.t.) (α, poly) 0.940 µΩ·m
Thermal conductivity	(300 K) 13.3  W·m−1·K−1
Thermal expansion	(r.t.) (α, poly) 12.7 µm/(m·K)
Speed of sound (thin rod)	(20 °C) 2130 m/s
Young's modulus	(α form) 49.7  GPa
Shear modulus	(α form) 19.5  GPa
Bulk modulus	(α form) 37.8  GPa
Poisson ratio	(α form) 0.274
Vickers hardness	412  MPa
Brinell hardness	441  MPa
CAS registry number	7440-19-9
Most-stable isotopes
Main article: Isotopes of samarium iso NA half-life DM DE (MeV) DP 144Sm 3.07% 144Sm is stable with 82 neutrons 146Sm syn 1.03×108y α 2.529 142Nd 147Sm 14.99% 1.06×1011y α 2.310 143Nd 148Sm 11.24% 7×1015y α 1.986 144Nd 149Sm 13.82% >2×1015 y α 1.870 145Nd 150Sm 7.38% 150Sm is stable with 88 neutrons 152Sm 26.75% 152Sm is stable with 90 neutrons 154Sm 22.75% 154Sm is stable with 92 neutrons
References

Samarium (pronounced /səˈmɛəriəm/) is a chemical element with the symbol Sm and atomic number 62.

Characteristics

Physical

Samarium is a rare earth metal, with a bright silver luster. Three crystal modifications of the metal also exist, with transformations at 734 and 922 °C, making it polymorphic. Individual samarium atoms can be isolated by encaspulating them into fullerene molecules.^[2]

Chemical

Samarium oxidizes in air and ignites at 150 °C. Even with long-term storage under mineral oil, samarium is gradually oxidized, with a grayish-yellow powder of the oxide-hydroxide being formed. The metallic appearance of a sample can be preserved by sealing it under an inert gas such as argon.

Samarium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form samarium hydroxide:

2 Sm(s) + 6 H₂O(g) → 2 Sm(OH)₃(aq) + 3 H₂(g)

Samarium metal reacts with all the halogens:

2 Sm(s) + 3 F₂(g) → 2 SmF₃(s) [white]

2 Sm(s) + 3 Cl₂(g) → 2 SmCl₃(s) [yellow]

2 Sm(s) + 3 Br₂(g) → 2 SmBr₃(s) [yellow]

2 Sm(s) + 3 I₂(g) → 2 SmI₃(s) [orange]

Samarium dissolves readily in dilute sulphuric acid to form solutions containing the pale green Sm(III) ions, which exist as a [Sm(OH₂)₉]³⁺ complexes:^[3]

2 Sm(s) + 3 H₂SO₄(aq) → 2 Sm³⁺(aq) + 3 SO₄^2-(aq) + 3 H₂(g)

Compounds

Compounds of Samarium include:

• Fluorides: SmF₂, SmF₃
• Chlorides: SmCl₂, SmCl₃
• Bromides: SmBr₂, SmBr₃
• Iodides: SmI₂, SmI₃
• Oxides: Sm₂O₃
• Sulfides: Sm₂S₃
• Selenides: Sm₂Se₃
• Tellurides: Sm₂Te₃

The most common oxidation state of samarium is +3, but +2 compounds are known too, such as SmI₂.

Isotopes

Naturally occurring samarium is composed of four stable isotopes, ¹⁴⁴Sm, ¹⁵⁰Sm, ¹⁵²Sm and ¹⁵⁴Sm, and three extremely long-lived radioisotopes, ¹⁴⁷Sm (1.06 × 10¹¹y), ¹⁴⁸Sm (7 × 10¹⁵y) and ¹⁴⁹Sm (>2 × 10¹⁵y), with ¹⁵²Sm being the most abundant (26.75% natural abundance).

¹⁵¹Sm has a halflife of 90 years, and ¹⁴⁵Sm has a halflife of 340 days. All of the remaining radioisotopes have half-lives that are less than 2 days, and the majority of these have half-lives that are less than 48 seconds. This element also has 5 meta states with the most stable being ^141mSm (t_½ 22.6 minutes), ^143m1Sm (t_½ 66 seconds) and ^139mSm (t_½ 10.7 seconds).

The primary decay mode before the most abundant stable isotope, ¹⁵²Sm, is electron capture, and the primary mode after is beta minus decay. The primary decay products before ¹⁵²Sm are element Pm (promethium) isotopes, and the primary products after are element Eu (europium) isotopes.

Natural Samarium has an activity of 128 Bq/g.

History

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). Although samarskite was first found in the Urals, by the late 1870s a new deposit had been located in North Carolina, and it was from that source that the samarium-bearing didymium had originated.

The samarskite mineral was named after Vasili Samarsky-Bykhovets, the Chief of Staff (Colonel) of the Russian Corps of Mining Engineers in 1845–1861. The name of the element is derived from the name of the mineral, and thus traces back to the name Samarsky-Bykhovets. In this sense samarium was the first chemical element to be named after a living person.

Prior to the advent of ion-exchange separation technology in the 1950s, samarium had no commercial uses in pure form. However, a by-product of the fractional crystallization purification of neodymium was a mixture of samarium and gadolinium that acquired the name of "Lindsay Mix" after the company that made it. This material is thought to have been used for nuclear control rods in some of the early nuclear reactors. Nowadays, a similar commodity product goes under the name of "Samarium-Europium-Gadolinium" concentrate (or SEG concentrate). This is prepared by solvent extraction from the mixed lanthanides extracted from bastnäsite (or monazite). Since the heavier lanthanides have the greater affinity for the solvent used, they are easily extracted from the bulk using relatively small proportions of solvent. Not all rare earth producers who process bastnäsite do so on large enough scale to continue onward with the separation of the components of SEG, which typically makes up only one or two percent of the original ore. Such producers will therefore be making SEG with a view to marketing it to the specialized processors. In this manner, the valuable europium content of the ore is rescued for use in phosphor manufacture. Samarium purification follows the removal of the europium. Currently, being in oversupply, samarium oxide is less expensive on a commercial scale than its relative abundance in the ore might suggest.

Occurrence

Samarskite

Samarium is never found free in nature, but, like other rare earth elements, is contained in many minerals, including monazite, bastnäsite and samarskite; monazite (in which it occurs up to an extent of 2.8%) and bastnäsite 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^[1]. Samarium can also be obtained by reducing its oxide with lanthanum.

Applications

Uses of Samarium include:

• Carbon-arc lighting for the motion picture industry (together with other rare earth metals).
• CaF₂ crystals for use in lasers.
• As a neutron absorber in nuclear reactors.
• For alloys.
• For headphone magnets.
• Samarium-cobalt magnets; SmCo₅ and Sm₂Co₁₇ are used in making permanent magnet materials that have high resistance to demagnetization when compared to other permanent magnet materials. These materials have high coercivities and intrinsic coercivities. Samarium-cobalt combinations have recently found use in high-end magnetic pickups for guitars and related musical instruments.
• Samarium(II) iodide is used as a reducing agent and coupling agent chemical reagent in organic synthesis, for example in the Barbier reaction.^[4]
• 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-neodymium dating is useful for determining the age relationships of rocks and meteorites.
• Radioactive Samarium-153 is used in medicine to treat the severe pain associated with cancers that have spread to bone. The drug is called "Quadramet".^[5]

Precautions

As with the other lanthanides, samarium compounds are of low to moderate toxicity, although their toxicity has not been investigated in detail.

References

Books

• N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, Pergamon Press, Oxford, UK, 1984.

External links

Wikimedia Commons has media related to: Samarium

Look up samarium in Wiktionary, the free dictionary.

• WebElements.com – Samarium
• It's Elemental – Samarium
• Reducing Agents > Samarium low valent