Samarium (Sm)
Samarium (Sm) is a lanthanide with atomic number 62 and a standard atomic weight of 150.36. At room temperature it is a solid that melts at 1,072 °C and boils at 1,794 °C.
Samarium key facts
Samarium at a glance
Identity
| Symbol | Sm |
|---|---|
| Atomic number (Z) | 62 |
| Atomic weight | 150.36 ± 0.02 (CIAAW 2024) |
| Category | Lanthanide |
| Group | — (f-block: lanthanide series) |
| Period | 6 |
| Block | f-block |
| CAS number | 7440-19-9 |
Atomic properties
| Electron configuration | [Xe] 4f6 6s2 Full: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f6 5s2 5p6 6s2 |
|---|---|
| Electrons per shell | 2, 8, 18, 24, 8, 2 |
| Oxidation states | +3 Less common: 0, +1, +2 |
| Electronegativity (Pauling) | 1.17 |
| First ionisation energy | 5.644 eV (544.5 kJ/mol) 2nd: 11.078 eV · 3rd: 23.55 eV |
| Atomic radius (empirical) | 185 pm |
| Covalent radius | 172 pm |
| Van der Waals radius | 236 pm |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Melting point | 1,072 °C · 1,961.6 °F · 1,345.15 K |
| Boiling point | 1,794 °C · 3,261.2 °F · 2,067.15 K |
| Density | 7.52 g/cm³ |
| Specific heat capacity | 0.197 J/(g·K) |
| Crystal structure | Rhombohedral |
Isotopes & abundance
| Natural occurrence | Primordial |
|---|---|
| Radioactive | No |
| Natural isotopes (abundance) | 152Sm 26.74%, 154Sm 22.74%, 147Sm 15% (radioactive), 149Sm 13.82%, 148Sm 11.25% (radioactive), 150Sm 7.37% |
| Stable isotopes | 5 |
| Known isotopes | 41 |
| Abundance in Earth's crust | 7.05 mg/kg |
| Abundance in seawater | 0.00000045 mg/L |
Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.
Samarium electron configuration
Samarium has 62 electrons. Written in short form, its ground-state configuration is [Xe] 4f6 6s2 — the electrons of the noble gas xenon, plus 4f6 6s2.Written out in full: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f6 5s2 5p6 6s2.
Discovery and name
1879 — Paul-Émile Lecoq de Boisbaudran · France.
The mineral samarskite, named after the mining official Vasili Samarsky-Bykhovets.
Known for
Samarium–cobalt magnets keep their strength at high temperatures. Samarium-153 relieves pain from bone cancers.
Isotopes of samarium
Naturally occurring samarium is a mix of 7 isotopes. Each has 62 protons; they differ in the number of neutrons:
| Isotope | Protons | Neutrons | Natural abundance | Stability |
|---|---|---|---|---|
| 152Sm | 62 | 90 | 26.74% | stable |
| 154Sm | 62 | 92 | 22.74% | stable |
| 147Sm | 62 | 85 | 15% | radioactive · half-life 106.6 billion years |
| 149Sm | 62 | 87 | 13.82% | stable |
| 148Sm | 62 | 86 | 11.25% | radioactive · half-life 6.3 × 10¹⁵ years |
| 150Sm | 62 | 88 | 7.37% | stable |
| 144Sm | 62 | 82 | 3.08% | stable |
41 isotopes of samarium are known in our data set (half-lives as published in nuclear data tables).
Samarium and its neighbours in the lanthanide series
Neighbouring elements in the same f-block series:
| Element | Z | Atomic weight | Melting point | Boiling point | Density | Electronegativity |
|---|---|---|---|---|---|---|
| Praseodymium | 59 | 140.91 | 931 °C | 3,520 °C | 6.773 g/cm³ | 1.13 |
| Neodymium | 60 | 144.24 | 1,016 °C | 3,074 °C | 7.01 g/cm³ | 1.14 |
| Promethium | 61 | [145] | 1,042 °C | 3,000 °C | 7.26 g/cm³ | 1.13 |
| Samarium | 62 | 150.36 | 1,072 °C | 1,794 °C | 7.52 g/cm³ | 1.17 |
| Europium | 63 | 151.96 | 822 °C | 1,529 °C | 5.24 g/cm³ | 1.2 |
| Gadolinium | 64 | 157.25 | 1,313 °C | 3,273 °C | 7.9 g/cm³ | 1.2 |
| Terbium | 65 | 158.93 | 1,359 °C | 3,230 °C | 8.23 g/cm³ | 1.1 |