Fermium (Fm)

Unknown

Fermium is the last element that can be synthesized by neutron bombardment of lighter elements, and with [Rn] 5f¹² 7s², fermium-257 (half-life 100.5 days) is the heaviest isotope producible in nuclear reactors. Beyond fermium, elements must be created by charged-particle bombardment, one atom at a time.

Key metrics

Density9.7g/cm³predicted

Melting point1,527Kpredicted

Boiling point1,125Kpredicted

Electronegativity1.3Paulingpredicted

Discovery

1952discovered

Discovered by: Lawrence Berkeley Lab
Reactivity profile: Highly radioactive
Reactivity: High
Bonding: Metallic

Electron configuration

\textcolor{#6b7280}{[Rn]}\; \textcolor{#a855f7}{5_{f}^{12}}\; \textcolor{#ef4444}{7_{s}^{2}}

[Rn] 5f12 7s2

Wave function

\Psi_{\text{Fm}} \approx \frac{1}{\sqrt{100!}} \det \left| \chi_1(\mathbf{r}_1) \dots \chi_{100}(\mathbf{r}_{100}) \right|

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

Crystal structure

Hexagonal Close-Packed

Lattice constantsa 1.00 · b 1.00 · c 1.63

Cell anglesα 90° · β 90° · γ 120°

Coordination number12

Atoms per cell2

Atomic packing factor0.74

Physical properties

Atomic radius: 187 pmpredicted
Ionization energy: 627 kJ/molpredicted
Electron affinity: 0 kJ/molpredicted
Crystal structure: Hexagonal close-packed (predicted)

Oxidation statespredicted

+2+3

Acid/base

Basic

Strongly acidicStrongly basic

State at 25 °CSolid

1527 K1125 K298 K

predicted

Emission spectrum

3 transitions

380450500550600650700780

VioletBlueGreenYellowRed

428.0nmFm I (blue)Violet60%

480.0nmFm IBlue40%

495.0nmFm I (blue-green)Cyan100%

Dominant line 495.0 nmRange 428–495 nmTransitions 3