Einsteinium
Element 99 · Actinide
Einsteinium was discovered in the fallout of the first thermonuclear explosion, where intense neutron fluxes built heavy atoms from uranium. It is a soft, silvery, intensely radioactive metal produced today only in nanogram to microgram amounts. It decays within months, so its chemistry has been studied only with tracer-scale samples. It has no practical applications beyond basic research.
Key facts
| Atomic number | 99 |
|---|---|
| Atomic weight | [252] |
| Category | Actinide |
| Group / Period | — / 7 |
| Block | f |
| Electron configuration | [Rn] 5f11 7s2 |
| Common oxidation states | +3 |
| State at STP | Solid |
| Electronegativity | 1.3 |
| Density | 8.84 g/cm3 |
| Melting point | 860 °C |
| Boiling point | 996 °C (estimated) |
Occurrence
Einsteinium is entirely synthetic, made by neutron irradiation of lighter actinides in high-flux reactors. Its longest-lived isotope, einsteinium-252, has a half-life of about 472 days.
Applications
Basic research on heavy-actinide chemistry
Target for producing fermium and mendelevium
No commercial applications
Common compounds
- Einsteinium(III) oxide (Es2O3, tracer scale)
- Einsteinium(III) fluoride (EsF3, tracer scale)
Einsteinium was found in 1952 in debris from the Ivy Mike hydrogen bomb test and named after Albert Einstein, who had no direct role in its discovery.
Data source: IUPAC standard atomic weights 2021