Samarium (Sm)
“The first element in history to be named after a real person — a Russian mining engineer — now famous for magnets that shrug off heat.”
How its electrons are arranged
Computed from the aufbau principle, with known real-world exceptions applied automatically.
Characteristics
- Electron configuration [Xe] 4f⁶ 6s² — a period-6 f-block lanthanide whose atoms normally surrender three electrons to become Sm³⁺.
- Samarium–cobalt magnets (SmCo₅ and Sm₂Co₁₇) are not the strongest at room temperature, but they keep their magnetism up to roughly 300 °C, where neodymium magnets give up.
- It is one of the few lanthanides with a genuinely useful +2 state: samarium(II) iodide (SmI₂, “Kagan’s reagent”) is a famous single-electron reducing agent in organic chemistry.
- The radioisotope samarium-153, with a half-life of about 46 hours, emits beta radiation that travels to bone, easing the pain of cancers that have spread there.
A hard, bright silvery metal that slowly grows a grey oxide film in air. Among the rare-earth metals samarium is unusually hard, so it holds its polish far longer than softer cousins like europium.
Where you meet it
✦ Uses
- Samarium–cobalt permanent magnets in headphones, guitar pickups and compact high-temperature electric motors, where heat would destroy cheaper magnets.
- A samarium-153 injection (a bone-seeking radiopharmaceutical) given to cancer patients to relieve pain when the disease has spread into bones.
- Samarium(II) iodide, the laboratory one-electron reducing reagent, used across university organic-synthesis benches.
- A minor ingredient of mischmetal — the spark-showering flint of household gas lighters — with samarium oxide also serving in catalysts and infrared-absorbing glass.
◍ Everyday examples
- The sparks that light a kitchen gas lighter come from a mischmetal flint — a rare-earth alloy that always carries a little samarium.
- A studio-quality headphone or a friend’s electric-guitar pickup may hide a samarium–cobalt magnet no bigger than a shirt button.
History & name
In 1879 the French spectroscopist Paul-Émile Lecoq de Boisbaudran, working in Paris on the mineral samarskite from Russia’s Ural Mountains, noticed unfamiliar sharp lines in its spectrum — the fingerprint of a new element. He named it samarium after the mineral, which decades earlier had been named in honour of Vasili Samarsky-Bykhovets, Chief of Staff of Russia’s Corps of Mining Engineers. That made samarium the first chemical element ever named after a person; the truly pure metal only followed much later, once modern separation methods arrived.