Samarium
Samarium is a chemical element with symbol Sm and atomic number 62. It is a moderately hard silvery metal that readily oxidizes in air. Being a typical member of the lanthanide series, samarium usually assumes the oxidation state +3.
At a glance
- Atomic number
- 62
- Atomic mass
- 150.362 u
- Phase
- Solid
- Density
- 7.52 g/cm³
- Melting point
- 1,345 K
- Boiling point
- 2,173 K
- First ionization energy
- 544.5 kJ/mol
- Electronegativity
- 1.17
- Electron affinity
- 15.63 kJ/mol
- Molar heat capacity
- 29.54 J/(mol·K)
- Period
- 6
- Appearance
- silvery white
Conditions and isotopes affect measured properties. Some properties of short-lived elements are predicted. Electronegativity uses the Pauling scale.
Samarium’s orbitals use a hydrogen-like approximation. Every orbital of each visible subshell is shown: in Shapes as the surface holding half its probability, with light and dark shades for opposite signs of the wavefunction; in Cloud as dots where its electrons are likely to be. Sizes are stepped by shell, like the Shell model.
54 is the [Xe] core total across five shells.
Preparing the orbital view…
62 protons90 neutrons
Samarium-152: its most common form in nature, or its longest-lived if it has none. The nucleus is drawn far too big: it’s about 100,000 times smaller than the atom.
Turn up the heat
A step of 1 K is the same size as 1 °C, so the two scales are always 273.15 apart. Fahrenheit is different: its degrees are smaller and it starts elsewhere, so water freezes at 273.15 K, 0 °C and 32 °F.25 °C · 77 °FSolid
At this temperature, samarium is a solid.
At normal atmospheric pressure (1 atm). The temperature scale is logarithmic. The particle box is schematic: real samples hold vastly more atoms, and spacing and speeds are not to scale.
Pull the electrons off
SmNeutral atom · no charge
A neutral samarium atom. Removing its first electron takes 545 kJ/mol.
Samarium’s outer shell holds 2 electrons. Electron 3 is the first from an inner shell: it sits closer to the nucleus with less shielding, so removing it takes 2.1× as much energy as the one before. Each dashed line on the chart marks another jump, into a shell even closer to the nucleus.
What does this tell us?
- Within a shell the steps rise gently. Each electron removed leaves fewer electrons pushing the others away, while the nucleus pulls just as hard, so the next one is held a little more tightly.
Show the values as a table
| Electron | Shell | Energy (kJ/mol) | × previous | Value |
|---|---|---|---|---|
| 1 | 6 | 545 | – | Measured |
| 2 | 6 | 1,069 | 2 | Estimated |
| 3 | 5 | 2,272 | 2.1 | Estimated |
| 4 | 5 | 4,018 | 1.8 | Estimated |
| 5 | 5 | 6,050 | 1.5 | Estimated |
| 6 | 5 | 8,394 | 1.4 | Calculated |
| 7 | 5 | 9,938 | 1.2 | Calculated |
| 8 | 5 | 11,385 | 1.1 | Calculated |
| 9 | 5 | 13,604 | 1.2 | Calculated |
| 10 | 5 | 15,245 | 1.1 | Calculated |
| 11 | 4 | 17,271 | 1.1 | Calculated |
| 12 | 4 | 20,069 | 1.2 | Calculated |
| 13 | 4 | 22,867 | 1.1 | Calculated |
| 14 | 4 | 24,797 | 1.1 | Calculated |
| 15 | 4 | 26,630 | 1.1 | Calculated |
| 16 | 4 | 29,573 | 1.1 | Estimated |
| 17 | 4 | 45,734 | 1.5 | Calculated |
| 18 | 4 | 48,822 | 1.1 | Calculated |
| 19 | 4 | 52,392 | 1.1 | Calculated |
| 20 | 4 | 56,058 | 1.1 | Calculated |
| 21 | 4 | 59,531 | 1.1 | Calculated |
| 22 | 4 | 63,487 | 1.1 | Calculated |
| 23 | 4 | 67,733 | 1.1 | Calculated |
| 24 | 4 | 71,592 | 1.1 | Calculated |
| 25 | 4 | 75,452 | 1.1 | Calculated |
| 26 | 4 | 79,311 | 1.1 | Calculated |
| 27 | 4 | 94,170 | 1.2 | Calculated |
| 28 | 4 | 98,029 | 1 | Calculated |
| 29 | 4 | 102,274 | 1 | Calculated |
| 30 | 4 | 106,423 | 1 | Calculated |
| 31 | 4 | 113,853 | 1.1 | Calculated |
| 32 | 4 | 118,291 | 1 | Calculated |
| 33 | 4 | 128,518 | 1.1 | Calculated |
| 34 | 4 | 133,300 | 1 | Estimated |
| 35 | 3 | 228,767 | 1.7 | Calculated |
| 36 | 3 | 237,933 | 1 | Calculated |
| 37 | 3 | 247,871 | 1 | Calculated |
| 38 | 3 | 258,195 | 1 | Calculated |
| 39 | 3 | 268,422 | 1 | Calculated |
| 40 | 3 | 278,553 | 1 | Calculated |
| 41 | 3 | 292,158 | 1 | Calculated |
| 42 | 3 | 302,674 | 1 | Calculated |
| 43 | 3 | 313,867 | 1 | Calculated |
| 44 | 3 | 324,480 | 1 | Calculated |
| 45 | 3 | 354,005 | 1.1 | Calculated |
| 46 | 3 | 363,364 | 1 | Calculated |
| 47 | 3 | 373,688 | 1 | Calculated |
| 48 | 3 | 383,143 | 1 | Calculated |
| 49 | 3 | 407,843 | 1.1 | Calculated |
| 50 | 3 | 418,457 | 1 | Calculated |
| 51 | 3 | 438,815 | 1 | Calculated |
| 52 | 3 | 449,139 | 1 | Calculated |
| 53 | 2 | 1,012,517 | 2.3 | Calculated |
| 54 | 2 | 1,038,375 | 1 | Calculated |
| 55 | 2 | 1,067,128 | 1 | Calculated |
| 56 | 2 | 1,093,854 | 1 | Calculated |
| 57 | 2 | 1,183,296 | 1.1 | Calculated |
| 58 | 2 | 1,214,557 | 1 | Calculated |
| 59 | 2 | 1,253,537 | 1 | Calculated |
| 60 | 2 | 1,279,670 | 1 | Calculated |
| 61 | 1 | 5,208,869 | 4.1 | Calculated |
| 62 | 1 | 5,327,370 | 1 | Calculated |
Successive ionization energies of gas-phase atoms and ions from the NIST Atomic Spectra Database. Solid bars are measured; hatched bars were estimated from nearby measurements or calculated from quantum theory, as is usual for highly charged ions. Electrons are taken from the outermost shell first, a simplification: electrons in different subshells of the same shell also differ in energy. On the log scale each gridline is 10 times the one below.
Rare-earth magnets: strength and heat
Samarium–cobalt magnets were the first rare-earth magnets. Neodymium magnets later beat them for strength, but when things get hot, samarium–cobalt wins.
Same job, different sizeA magnet’s strength for its size is measured by its maximum energy product, (BH)max, in kilojoules per cubic metre: the magnetic energy it can store in each bit of its volume. To do the same job you need roughly as much less material as this number is higher. Each magnet uses the best grade of its kind.
- Ferriteiron-oxide ceramic, as in fridge magnets40 kJ/m³ · 11× the volume
- Alnicoaluminium–nickel–cobalt alloy, the strongest before the 1960s88 kJ/m³ · 5× the volume
- Samarium–cobaltthe first rare-earth magnet, from the 1960s240 kJ/m³ · 1.8× the volume
- Neodymiumneodymium–iron–boron, from 1984440 kJ/m³ · Smallest
Each magnet is drawn at the size it would need to be to hold the same weight. A neodymium magnet does the job of a ferrite one 11 times its volume, which is how headphones, phones and hard drives got so small.
Heat it up
Warm magnets get weaker. A little warmth is harmless: the strength comes back when they cool. Go past a magnet’s limit and some is lost for good; at its Curie temperature it stops being a magnet at all.
- Neodymiumstandard grade · safe to 80 °C
100%Full strength - Neodymium + dysprosiumhigh-temperature grade · safe to 230 °C
100%Full strength - Samarium–cobaltSm₂Co₁₇ · safe to 350 °C
100%Full strength
All three at full strength. Warm them up.
Where they’re used
- Small and strong
Neodymium magnets move the read head in hard drives and drive the tiny speakers in earbuds and phones: nothing else is as strong for its size.
- Motors that run hot
Electric-car motors and wind-turbine generators get warm, so their neodymium magnets often contain dysprosium or terbium. Those are rarer still, which makes the magnets costly.
- Where heat matters most
Samarium–cobalt came first, in the 1960s. It is pricier and weaker, but it works in very hot and very cold places. The hunt for something cheaper led to neodymium magnets in 1984.
Energy products, Curie temperatures and temperature coefficients from Wikipedia’s comparison tables of permanent magnets; working limits from the grade descriptions there. Real magnets vary by grade, shape and use. Past a magnet’s limit, the lasting loss is drawn starting small and growing to all of it at the Curie temperature, a simplification. Sizes assume the same job for each magnet.
How does it compare?
Density
7.52 g/cm³44th highest of 99
Melting point
1,345 K41st highest of 96
Boiling point
2,173 K42nd lowest of 97
Electronegativity
1.1720th lowest of 96
First ionization energy
545 kJ/mol16th lowest of 99
Elements 1–99 from the reference data; heavier elements are left out because only a few atoms have ever been made, so their bulk properties are predictions. First ionization energies come from NIST. Density uses a logarithmic scale, because gases are around a thousand times less dense than solids; gas densities are at 0 °C and 1 atm. Melting and boiling points are at normal pressure. Everyday temperatures and light sources in the pictures are approximate. Hover over a dot to see the element, or click it to compare.
Keep exploring
Explore the stories, imagery, and reference data in more depth. Properties with no value in the reference are marked unavailable.
- SamariumRoyal Society of Chemistry
- SamariumWikipedia
- Quantum numbers and electron configurationsPurdue
- Hydrogenic wavefunctionsNIST
- Ionization energiesNIST Atomic Spectra Database