Samarium
Atomic Data
| Atomic Number | 62 |
| Symbol | Sm |
| Atomic Weight | 150.36 u |
| Density (STP) | 7.52 g/cm³ |
| Melting Point | 1071.85 °C (1345 K) |
| Boiling Point | 1793.85 °C (2067 K) |
| Electronegativity | 1.17 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f6 5s2 5p6 6s2 |
| Oxidation States | +2, +3 |
| Phase at STP | Solid |
| Category | Lanthanoid |
| Period / Group | 6 / None |
| CAS Number | 7440-19-9 |
Electron Configuration
[Xe] 4f6 6s2
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 10 | 28 |
| N | 4 | 4s | 2 | 30 |
| N | 4 | 4p | 6 | 36 |
| N | 4 | 4d | 10 | 46 |
| N | 4 | 4f | 6 | 52 |
| O | 5 | 5s | 2 | 54 |
| O | 5 | 5p | 6 | 60 |
| P | 6 | 6s | 2 | 62 |
| Total | 62 | 62 | ||
Isotopes of Samarium
Samarium has seven naturally occurring stable isotopes. The most abundant is ¹⁵²Sm, comprising 26.75% of all naturally occurring Samarium.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Samarium-144 | ¹⁴⁴Sm | 62 | 82 | 3.08 | Stable |
| Samarium-147 | ¹⁴⁷Sm | 62 | 85 | 14.99 | Stable |
| Samarium-148 | ¹⁴⁸Sm | 62 | 86 | 11.24 | Stable |
| Samarium-149 | ¹⁴⁹Sm | 62 | 87 | 13.82 | Stable |
| Samarium-150 | ¹⁵⁰Sm | 62 | 88 | 7.38 | Stable |
| Samarium-152 | ¹⁵²Sm | 62 | 90 | 26.75 | Stable |
| Samarium-154 | ¹⁵⁴Sm | 62 | 92 | 22.74 | Stable |
Abundance & Occurrence
Samarium is present in Earth's crust at approximately 7.9 ppm by mass and at approximately 0.5 ppm by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Dust inhalation: Samarium metal powder and samarium compounds are respiratory irritants; handle powders with ventilation and appropriate respiratory protection to prevent inhalation of fine particles.
- Samarium-153: medical radiation: Sm-153 (t½ = 46 h, beta/gamma) is used in cancer pain palliation for bone metastases; staff administering Sm-153 lexidronam must follow radiation protection protocols and patients require post-treatment monitoring.
- Fire hazard: Samarium metal powder is flammable; metal fires require Class D extinguishing agents.
- Samarium-cobalt magnets: SmCo permanent magnets can crush fingers and hands; keep magnets away from electronic devices and active medical implants.
Samarium in the Real World
Real-World Uses
- Samarium-cobalt permanent magnets: SmCo₅ and Sm₂Co₁₇ permanent magnets retain high coercivity at temperatures up to 300 °C, making them preferred over Nd-Fe-B magnets in jet aircraft actuators, high-temperature sensors, and motors where thermal stability is critical.
- Cancer pain palliation: Samarium-153 (Quadramet, t½ = 46.3 h) is a radiopharmaceutical that concentrates in bone metastases and delivers a localised beta-radiation dose to reduce severe bone pain in patients with breast, prostate, and lung cancers.
- Nuclear reactor control: Samarium-149, a significant neutron absorber produced from fission product decay, must be accounted for in reactor physics calculations; samarium compounds are studied as burnable absorbers in compact reactor designs.
- Infrared-absorbing glass: Samarium oxide glass absorbs near-infrared radiation and is used in laser protective eyewear for Nd:YAG and other near-IR laser wavelengths, and as a spectroscopic calibration standard.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is samarium used for?
Samarium's most important use is in samarium-cobalt (SmCo) permanent magnets, which are extremely resistant to demagnetisation and can operate at high temperatures: making them preferred over neodymium magnets in applications like jet engine components and military equipment. Samarium-153 is used in cancer pain relief treatment (it localises in bone metastases and delivers beta radiation). Samarium oxide is used in optical glass and as a neutron absorber.
Are samarium-cobalt magnets better than neodymium magnets?
Samarium-cobalt magnets are not as strong as neodymium magnets in terms of maximum energy product, but they outperform NdFeB magnets in specific applications. SmCo magnets are superior at elevated temperatures (they maintain performance up to about 300–350 °C versus about 80–200 °C for NdFeB), are more resistant to corrosion (and need no protective coating), and have better resistance to demagnetisation. They are preferred in aerospace, defence, and high-temperature industrial motors.
How was samarium discovered?
Samarium was discovered in 1879 by French chemist Paul Emile Lecoq de Boisbaudran, who isolated it spectroscopically from the mineral samarskite. The mineral: and hence the element: were named after Colonel Vasili Samarsky-Bykhovets, a Russian mining official who had provided the mineral samples for study. Samarium was thus the first chemical element to be named after a person, albeit indirectly via the mineral.
What is samarium-153 used for in medicine?
Samarium-153 lexidronam (trade name Quadramet) is a radiopharmaceutical used to relieve bone pain in patients with cancer that has spread to the bone. The drug is taken up by bone at sites of active bone turnover: precisely where metastases occur: and the beta radiation from Sm-153 damages the cancer cells causing pain. It also has some antitumour activity. The 46.3-hour half-life provides a treatment window of a few days.