Samarium ($Sm$)
The first element named after a person—a silvery powerhouse that fuels the light of high-end cinema and holds its magnetic grip even in the heat of a jet engine.
Samarium is a silvery-white lanthanide that made history by becoming the first chemical element to be named after a real person. In 1879, French chemist Paul-Émile Lecoq de Boisbaudran isolated it from the mineral samarskite. The mineral itself was named in honor of Vasili Samarsky-Bykhovets, a Russian mining engineer. While it may not have the name recognition of its neighbor neodymium, samarium is a technological titan in its own right.
Located in Group 3 and Period 6, samarium is part of the f-block. It is relatively stable in dry air but, like most rare-earth metals, it quickly develops an oxide layer in moist environments. It is the 40th most abundant element in the Earth's crust, found alongside other lanthanides in monazite and bastnäsite ores.
Atomic & Physical Properties
Samarium is a medium-hard metal with a hardness similar to that of iron. One of its most distinctive chemical traits is the accessibility of its divalent ($+2$) state, which produces beautiful blood-red solutions.
| Property | Value |
|---|---|
| Atomic Number | 62 |
| Standard Atomic Weight | 150.36 |
| Electron Configuration | $[Xe] 4f^6 6s^2$ |
| Common Oxidation States | +3 (Stable), +2 (Accessible) |
| Melting Point | 1345 K (1072 °C) |
| Boiling Point | 2173 K (1900 °C) |
| Density | 7.52 g/cm³ |
The Unusual +2 Oxidation State
While most lanthanides are strictly trivalent ($+3$), samarium is one of the few that can easily form divalent compounds. Samarium(II) iodide ($SmI_2$) is a legendary reagent in organic chemistry. Known as "Kagan's Reagent," it is a powerful one-electron reducing agent used to create complex carbon-carbon bonds in the synthesis of pharmaceuticals.
The transition from the blood-red $Sm^{2+}$ to the pale yellow $Sm^{3+}$ provides chemists with a built-in visual indicator of the reaction's progress.
Chemical Reactivity
Samarium is a highly electropositive metal. It reacts slowly with cold water and rapidly with hot water to produce hydrogen gas.
1. Reaction with Air
Samarium tarnishes slowly in air to form samarium(III) oxide ($Sm_2O_3$).
2. Reaction with Acids
The metal dissolves readily in dilute sulfuric acid to form pale yellow solutions containing the $Sm^{3+}$ aqua ion.
3. Reaction with Halogens
Samarium reacts vigorously with all the halogens to form trihalides ($SmX_3$).
Samarium-Cobalt (Sm-Co) Magnets
The High-Temperature Champion
In the 1970s, the Samarium-Cobalt magnet was the strongest permanent magnet in the world. Although it was later surpassed in raw strength by Neodymium magnets, Samarium-Cobalt remains the "gold standard" for extreme environments.
Why? Neodymium magnets lose their magnetism as they heat up. However, Sm-Co magnets possess a very high Curie temperature, meaning they can function perfectly at temperatures as high as 350°C to 500°C. This makes them essential for jet engine sensors, high-performance electric motors, and the guidance systems of missiles.
Medicine: Samarium-153
Samarium has a vital role in palliative medicine. The radioisotope Samarium-153 is used in a drug called Samarium ($^{153}Sm$) Lexidronam (Quadramet). It is used to treat the intense bone pain associated with cancers that have spread to the skeleton.
Because samarium is chemically similar to calcium, the drug targets the areas of the bone where cancer is active, delivering localized beta radiation that kills cancer cells and shrinks tumors, providing significant pain relief for patients.
Nuclear Physics: A Neutron Poison
In nuclear engineering, samarium-149 is known as a "neutron poison." It has an extremely high neutron absorption cross-section. In a reactor, it is produced as a fission byproduct. Because it absorbs the neutrons needed to sustain the chain reaction, nuclear engineers must carefully account for "samarium poisoning" to ensure the reactor remains stable and efficient.
This is the sixty-second part of our "Elements and Their Properties" series. From the engines of a fighter jet to the targeted treatment of cancer, samarium is a silent enabler of modern high-tech life. To master the electron configurations of the lower lanthanide series, visit our Success Blueprint.
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