Samarium (Sm)

Silvery white

Samarium forms ultra-strong magnets and is used in nuclear reactor control rods to absorb neutrons, and with six unpaired 4f electrons, SmCo₅ magnets maintain performance at temperatures up to 550°C where neodymium magnets fail. Samarium-149 has one of the highest thermal neutron absorption cross-sections (40,000 barns).

Key metrics

Density7.52g/cm³

Melting point1,345K

Boiling point2,067K

Electronegativity1.17Pauling

Discovery

1879discovered

Discovered by: Paul-Émile Lecoq de Boisbaudran
Reactivity profile: Oxidizes in air
Reactivity: High
Bonding: Metallic

Electron configuration

\textcolor{#6b7280}{[Xe]}\; \textcolor{#a855f7}{4_{f}^{6}}\; \textcolor{#ef4444}{6_{s}^{2}}

[Xe] 4f6 6s2

Wave function

\Psi_{\text{Sm}} \approx \frac{1}{\sqrt{62!}} \det \left| \chi_1(\mathbf{r}_1) \dots \chi_{62}(\mathbf{r}_{62}) \right|

Probability density $|\Psi|^2$ across the Sm valence shell.

Crystal structure

Rhombohedral

Lattice constantsa 1.00 · b 1.00 · c 1.00

Cell anglesα = β = γ = 61.5°

Coordination number—

Atoms per cell—

Atomic packing factor0.53

Physical properties

Atomic radius: 180 pm
Ionization energy: 545 kJ/mol
Electron affinity: 50 kJ/mol
Crystal structure: Rhombohedral

Oxidation states

+2+3

Acid/base

Basic

Strongly acidicStrongly basic

State at 25 °CSolid

1345 K2067 K298 K

Emission spectrum

3 transitions

380450500550600650700780

VioletBlueGreenYellowRed

483.7nmSm I (blue)Blue40%

528.6nmSm I (green)Green60%

566.1nmSm I (yellow)Yellow100%

Dominant line 566.1 nmRange 484–566 nmTransitions 3