ChemSphere
62Sm150.362

Samarium

Lanthanide · Period 6 · f-block

The rare earth that made the first super-strong permanent magnets

Atomic mass
150.362 u
State at 25 °C
Solid
Electronegativity
1.17
Melting point
1,071.9 °C
Boiling point
1,899.9 °C
Configuration
[Xe] 4f6 6s2
Building atom…
62 protons 88 neutrons 62 electrons

Nucleus drawn at reduced count for clarity. Drag to rotate.

Samarium, explained

Video lesson in production

Bhavya’s explainer for this element will play here.

Overview

Samarium is a silvery lanthanide with the configuration [Xe]4f6 6s2. Like its neighbours it usually forms the Sm3+ ion, but because its 4f shell is one electron short of the especially stable half-filled 4f7 arrangement, it can also exist as Sm2+. That divalent state is a powerful but gentle electron donor: samarium(II) iodide, introduced by Henri Kagan in 1977, is now a standard reagent in organic synthesis for joining carbon atoms and reducing functional groups under mild conditions.

The metal is moderately reactive. It tarnishes slowly in air, burns when heated above about 150 °C, and reacts with water to release hydrogen. Its most important property is magnetic. Combined with cobalt as SmCo5 or Sm2Co17, it forms permanent magnets that resist demagnetisation and keep working at temperatures where neodymium magnets weaken. Samarium-149, a fission product, also absorbs neutrons strongly, so its build-up must be accounted for in every nuclear reactor.

Discovery

French chemist Paul-Émile Lecoq de Boisbaudran isolated samarium oxide in 1879 from the mineral samarskite and identified the new element by its sharp spectral lines. Samarskite had been named after Vasili Samarsky-Bykhovets, a Russian mining official who supplied the original specimens. That made samarium the first element named, indirectly, after a real person. The mineral later proved to contain several other rare earths, including europium and gadolinium.

Where it’s found
About 7 parts per million of Earth's crust; it is extracted mainly from monazite and bastnäsite by ion exchange and solvent extraction.
What it’s used for
  • Samarium-cobalt magnets
  • Bone-cancer pain therapy
  • Organic synthesis reagent (SmI2)
  • Reactor neutron absorbers
  • Infrared-absorbing glass
In living things
No known biological role. Its compounds have low to moderate toxicity.
Safety
The metal powder is flammable and can ignite in air; bulk metal is fairly safe to handle with ordinary precautions.

How it compares

Where Samarium sits among all 118 elements on the trends that shape the table.

  • Electronegativity1.17Pauling

    #81 of 100 elements with data

  • Ionization energy545kJ/mol

    #88 of 104 elements with data

  • Atomic radius185pm

    #11 of 95 elements with data

  • Electron affinity15.6kJ/mol

    #77 of 109 elements with data

  • Density7.52g/cm³

    #57 of 114 elements with data

  • Melting point1,350K

    #45 of 110 elements with data

Density
7.52 g/cm³
Atomic radius
185 pm
Covalent radius
172 pm
Molar heat
29.54 J/(mol·K)
Appearance
silvery white
Discovered by
Lecoq de Boisbaudran

Inside the atom

62 electrons arranged in 6 shells: 2 · 8 · 18 · 24 · 8 · 2.

Orbital diagram

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f6 · shorthand [Xe] 4f6 6s2

  1. 1s2
  2. 2s2
  3. 2p6
  4. 3s2
  5. 3p6
  6. 4s2
  7. 3d10
  8. 4p6
  9. 5s2
  10. 4d10
  11. 5p6
  12. 6s2
  13. 4f6

Each box is an orbital holding up to two electrons of opposite spin. Highlighted subshells hold the valence electrons that decide how Samarium bonds.

Ionization energies

Energy to remove each electron in turn, on a log scale. Each electron is harder to remove than the last, because the remaining ones feel more of the nucleus.

Signature reactions

The chemistry Samarium is known for.

  1. Redox · Single displacement

    Reaction with water

    Samarium reduces water to hydrogen gas while forming a pale yellow hydroxide. Bubbles appear only slowly at room temperature, showing that samarium is less reactive than the alkaline earth metals.

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

    Conditions: slow in cold water, faster when hot

  2. Redox · Combustion

    Burning in air

    Heated samarium burns to form samarium(III) oxide, a pale yellow powder. The oxide is the usual form in which samarium is sold and stored.

    4Sm(s)+3O2(g)2Sm2O3(s)

    Conditions: ignites above about 150 °C

  3. Redox · Synthesis

    Making Kagan's reagent

    Samarium metal strips the iodine from diiodoethane, releasing ethene and leaving samarium(II) iodide as a deep blue solution. Chemists use this solution directly to join carbon fragments in the synthesis of complex natural products.

    Sm(s)+C2H4I2(l)SmI2(aq)+C2H4(g)

    Conditions: 1,2-diiodoethane in tetrahydrofuran, room temperature

Where you’ll meet it

  • Samarskite-(Y)

    Samarskite-(Y)

    Samarium was discovered in this black mineral and named after it.

    Photo: Wikimedia Commons
  • Guitar pickup

    Guitar pickup

    Some premium electric-guitar pickups use samarium-cobalt magnets for their stable, low-noise field.

    Photo: Wikimedia Commons
  • Headphones

    Headphones

    Compact samarium-cobalt magnets have driven the speaker elements of many high-end headphones.

    Photo: Wikimedia Commons
  • Samarium-153 lexidronam

    Samarium-153 lexidronam

    This radioactive samarium drug homes in on bone and relieves pain from cancer that has spread to the skeleton.

    Photo: Wikimedia Commons

Research

No research on Samarium yet

When Bhavya publishes a project that studies Samarium, it will be linked here.

See all research