Einsteinium
Einsteinium is a synthetic element with symbol Es and atomic number 99. It is the seventh transuranic element, and an actinide. Einsteinium was discovered as a component of the debris of the first hydrogen bomb explosion in 1952, and named after Albert Einstein.
Identity
- Atomic mass
- [252] u
- Category
- Actinides
- Group
- 3
- Period
- 7
- Block
- f
- Oxidation States
- +2, +3
- Phase (25 °C)
- Solid
- Appearance
- silver-colored
Electronic Structure
- Electron configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f11
- Short configuration
- [Rn] 5f11 7s2
- Electrons per shell
- 2, 8, 18, 32, 29, 8, 2
- Electronegativity (Pauling)
- 1.30
- Electron affinity
- -28.6 kJ/mol
- 1st ionization energy
- 619 kJ/mol
Physical properties
- Melting point
- 859.9 °C (1133 K)
- Boiling point
- 995.9 °C (1269 K)
- Density
- 8.84 g/cm³
- Molar heat capacity
- —
Chemical behavior of einsteinium
Einsteinium has eleven outer electrons ([Rn] 5f¹¹ 7s²) and acts as +3, with +2 accessible in halides and oxides. Its electronegativity is low (1.30) and it is a soft paramagnetic metal with face-centered cubic structure. It is so radioactive that it releases about 1,000 W per gram: its bluish glow excites the surrounding air and its own radiation destroys its crystal lattice within weeks.
Reactivity
4 Es + 3 O₂ → 2 Es₂O₃
In air it oxidizes to sesquioxide. Decay heat keeps the sample warm and accelerates the reaction.
2 Es + 6 HCl → 2 EsCl₃ + 3 H₂
It dissolves in acids giving einsteinium(III) salts. The chloride is the route for studying its chemistry in solution.
²⁵³Es → ²⁴⁹Bk + α
Es-253 decays to berkelium-249 emitting alpha particles at a rate of ~3% per day: any sample changes composition within weeks.
²⁵³Bk + n → ²⁵⁴Bk → (β) → ²⁵⁴Es
Es-254 is obtained by double neutron capture and beta decay of berkelium in the reactor: the route for the Surveyor 5 marker isotope.
Notable compounds
| Compound | Formula | Use or importance |
|---|---|---|
| Einsteinium oxide | Es₂O₃ | Study of einsteinium chemistry |
| Einsteinium chloride | EsCl₃ | Solution transfers |
| Einsteinium oxalate | Es₂(C₂O₄)₃ | Curium separation |
| Einsteinium trifluoride | EsF₃ | Halide precursor |
| Es-254 source | ²⁵⁴Es | Surveyor 5 probe marker |
Electron shell distribution
View in the atom builderIsotopes
No einsteinium isotope is stable. Einsteinium-252 (²⁵²Es, 471.7 days) is the most stable but extremely scarce; einsteinium-253 (²⁵³Es, 20.47 days) is the usual one in experiments, since it is obtained by double neutron capture. Einsteinium-254 (²⁵⁴Es, 276 days) calibrated the Surveyor 5 probe spectrometer.
Occurrence and production
It does not exist in nature: einsteinium was born in the debris of the first thermonuclear explosion (Ivy Mike, 1952), where Es-253 atoms were detected among fission products. Today it is produced in micrograms by double neutron capture in Oak Ridge's High Flux Isotope Reactor, between berkelium and fermium.
History and origin of the name
Ghiorso and colleagues identified it in 1952 analyzing the debris of the Ivy Mike H-bomb test in the Pacific. It was the seventh transuranium element and the first named after a living person: Albert Einstein, in the full centennial of his birth (1879-1952).
Applications and relevance of einsteinium
Uses of the element
Es-254 was used as a calibration marker in the chemical analysis spectrometer of the lunar probe Surveyor 5 (1967): one of the few practical uses of a superheavy element outside the laboratory.
Uses of its compounds
Its compounds allow studying the chemistry of heavy actinides and calibrating radiochemical separations later applied to californium and the superheavy elements.
Health, safety and environment
Biological role
It has no biological function and is extremely radiotoxic: one gram generates a kilowatt of heat from decay. Work is done in micrograms with double containment.
Safety
It is handled only in Oak Ridge and Dubna, in cells with forced cooling due to its own heat. Radiation damages its own crystal lattice, so samples are used soon after production.
Environment
There are no spills: every microgram is traceable and waste is vitrified. Its production consumes entire reactors for months.
Frequently asked questions about Einsteinium
Why does einsteinium emit a visible glow?
Einsteinium-253 is so radioactive that it releases an enormous amount of energy per gram, approximately 1,000 watts per gram. That energy, together with the alpha and beta particles it emits, can excite the molecules of the surrounding air and produce a faint bluish glow. It is not a luminescent property of the metal itself, but the effect of its intense radioactivity on the immediate surroundings.
What role did einsteinium play in mendelevium's synthesis?
Einsteinium-253 was the target material used to synthesize mendelevium, element 101, in 1955. By bombarding einsteinium atoms with alpha particles (helium nuclei) in a cyclotron, the first mendelevium-256 atoms were formed. This experiment marked a milestone by demonstrating that elements beyond number 100 could be created through fusion of light nuclei with heavy actinides.
Why is einsteinium paramagnetic?
Einsteinium is paramagnetic because its unpaired electrons in the 5f shell generate a net magnetic moment. Unlike ferromagnetic materials, it does not retain magnetization when the external field is removed, but it does align temporarily with it. This property, together with its face-centered cubic crystal structure, makes it interesting for studying the magnetic behavior of heavy actinides.
Has einsteinium been used in space missions?
Yes. The einsteinium-254 isotope was employed as a calibration marker in the chemical analysis spectrometer of the lunar probe Surveyor 5 in 1967. Its characteristic emission served as a reference to calibrate the instrument's measurements. It is one of the few cases in which a superheavy element has had a practical application outside the laboratory.
Why is it so hard to study einsteinium?
Besides being produced in minuscule quantities, einsteinium-253 decays rapidly and transforms into berkelium-249 and then californium-249, at a rate of approximately 3% per day. This means any sample changes composition within weeks, complicating experiments. High radioactivity also damages the metal's crystal lattice, altering its physical properties over time.
What is the difference between einsteinium-252 and einsteinium-253?
Einsteinium-252 is the most stable isotope, with a half-life of 471.7 days, but it is very difficult to produce in significant quantities. Einsteinium-253, with a half-life of 20.47 days, is the one obtained most easily and used in most experiments. Isotope choice depends on the balance between availability and sample duration.
What relationship does einsteinium have with holmium?
Einsteinium shares many physical and chemical similarities with holmium, a lanthanide situated much earlier in the periodic table. Both are soft, paramagnetic metals with a similar crystal structure. This analogy helps scientists predict einsteinium's behavior, since holmium is much more abundant and easier to study. It is an example of how periodic trends allow inferring properties of nearly inaccessible elements.
Main sources consulted: PubChem, Royal Society of Chemistry, NIST, IUPAC. Last revision: November 2026.