Samarium
[Xe] 4f⁶ 6s² · 2 · 8 · 18 · 24 · 8 · 2
The lanthanide that gave the world its first rare-earth permanent magnets. Samarium-cobalt magnets are weaker than neodymium ones but work at 350 °C, where neodymium has already demagnetised.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 62
- Atomic mass
- 150.36 а.е.м.
- Electron configuration
- [Xe] 4f⁶ 6s²
- Electrons per shell
- 2 · 8 · 18 · 24 · 8 · 2
- Block
- f-block
- Group
- no data
- Period
- 6
- Electronegativity (Pauling)
- 1.17
- Electronegativity (Allen)
- 1.07
- Atomic radius
- 229 pm
- Covalent radius
- 198 pm
- Van der Waals radius
- 229 pm
- Ionisation energy 1
- 544.5 kJ/mol
- Ionisation energy 2
- 1 070 kJ/mol
- Ionisation energy 3
- 2 260 kJ/mol
- Ionisation energy 4
- 3 990 kJ/mol
- Electron affinity
- 50 kJ/mol
- Common oxidation states
- +3
- Oxidation states
- +2, +3, +4
Physical properties
- State at 25 °C
- solid
- Density
- 7.52 g/cm³
- Melting point
- 1 345 K · 1 071.9 °C
- Boiling point
- 2 173 K · 1 899.9 °C
- Speed of sound
- 2 130 m/s
Thermal properties
- Heat of fusion
- 8.62 kJ/mol
- Heat of vaporisation
- 165 kJ/mol
- Specific heat capacity
- 0.197 J/(g·K)
- Thermal conductivity
- 13.3 W/(m·K)
Mechanical properties
- Young's modulus
- 49.7 GPa
- Shear modulus
- 19.5 GPa
- Bulk modulus
- 37.8 GPa
- Poisson ratio
- 0.27
- Mohs hardness
- no data
- Brinell hardness
- 441 MPa
Electrical and magnetic properties
- Electrical resistivity
- 940 nΩ·m
- Magnetic ordering
- paramagnetic
- Curie point
- no data
- Néel point
- 14.8 K
- Superconducting point
- no data
Crystal structure
- Crystal structure
- rhombohedral
- Lattice constants
- a = 362.1 pm · c = 2 625 pm
Abundance
- In the crust
- 7.05 mg/kg
- In the ocean
- 4.5·10⁻⁷ mg/L
- In the universe
- 0.5 mg/kg
- In the human body
- no data
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 144Sm | 3.07 % | stable | — |
| 147Sm | 14.99 % | 105.84 Gyr | α |
| 148Sm | 11.24 % | 6.972·10⁶ Gyr | α |
| 149Sm | 13.82 % | stable | — |
| 150Sm | 7.38 % | stable | — |
| 152Sm | 26.75 % | stable | — |
| 154Sm | 22.75 % | stable | — |
Samarium-147 is radioactive with a 106-billion-year half-life and underpins samarium-neodymium dating. Samarium-149 is a neutron poison that builds up in a running reactor.
Discovery
- Year of discovery
- 1879
- Discovered by
- Paul-Émile Lecoq de Boisbaudran
- Where
- France
- Origin of the name
- from the mineral samarskite, named after the mining engineer Vasili Samarsky-Bykhovets
History
Lecoq de Boisbaudran isolated samarium in 1879 from samarskite, a mineral named after the mining engineer Vasili Samarsky-Bykhovets. It is the first element named, if indirectly, after a specific person.
Where it occurs
7 mg/kg of the crust, travelling with the other light lanthanides.
How it is produced
By solvent-extraction separation of rare-earth concentrates, then reduction of the oxide with lanthanum in vacuum.
Role in living things
No biological role.
Safety
Of low toxicity. The powdered metal is pyrophoric.
Uses
- SmCo magnets for aerospace, defence and anything that runs hot: they hold magnetisation to 350 °C
- Reactor control rods: samarium-149 is a strong neutron absorber
- Dehydration and dehydrogenation catalysts
- Samarium-153 in palliative treatment of bone metastases
Curiosities
- Samarskite is named after Vasili Samarsky-Bykhovets — that is how a Russian engineer's surname entered the periodic table.
- Samarium-cobalt magnets arrived in the 1960s and were the first rare-earth magnets of any kind.
- Samarium-149 accumulates in a reactor and depresses reactivity, which core management has to account for.
- Natural samarium is faintly radioactive because of ¹⁴⁷Sm.