Name: Einsteinium
Symbol: Es
Atomic Number: 99
Atomic Weight: 252.000000
Family: Rare Earth Elements
CAS RN: 7429-92-7
Description: A radioactive rare earth metal.
State (25C): Solid
Oxidation states: +2, +3

Molar Volume:  unknown
Valence Electrons: 5f117s2

Boiling Point: unknown
Melting Point: 1133oK, 860oC, 1580oF

Electron Energy Level: 2, 8, 18, 32, 29, 8, 2
Isotopes: 19 + None Stable + 3 Meta States
Heat of Vaporization: unknown
Heat of Fusion: unknown
Density: unknown
Specific Heat: unknown
Atomic Radius: ~860 pm
Ionic Radius: 0.925
Electronegativity: 1.3 (Pauling); 1.2 (Allrod Rochow)

1s2 2s2p6 3s2p6d10 4s2p6d10f14 5s2p6d10f11 6s2p6 7s2


Einsteinium, named for Albert Einstein, was the seventh transuranic element of the actinide series to be discovered.  It was first identified in December 1952 by Albert Ghiorso at the University of California, Berkeley and another team headed by G.R. Choppin at Los Alamos National Laboratory.  Both were examining debris from the first thermonucleaar explosion (hydrogen bomb test), which took place in the Pacific in November 1952 (Operation Ivy).  They discovered the isotope  253Es (half-life 20.5 days) that was made by the nuclear fusion of 15 neutrons with 238U (which then went through seven beta decays).  These findings were kept secret until 1955 due to the Cold War.

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Albert Einstein

In 1961, a sufficient amount of einsteinium was synthesized to prepare a microscopic amount of 253Es.  This sample weighed about 0.01 mg.  A special magnetic-type balance was used in making this determination.  253Es so produced was used to produce mendelevium (Element 101).  About 3 mg of einsteinium has been produced at Oak Ridge National Laboratories by irradiating for several years kilogram quantities of 239Pu in a reactor to produce 242Pu.   This was then fabricated into pellets of plutonium oxide and aluminum powder, and loaded into target rods for an initial 1-year irradiation at the Savannah River Plant, followed by irradiation in a HFIR (High Flux Isotopic Reactor).  After 4 months in the HFIR the targets were removed for chemical separation of the einsteinium from californium. Nineteen isotopes and isomers of einsteinium are now recognized. 252Es has the longest half-life (276 days). Tracer studies using 253Es show that einsteinium has chemical properties typical of a heavy trivalent, actinide element.


  • EsBr2 Einsteinium (II) Bromide
  • EsBr3 Einsteinium (III) Bromide
  • EsCl2 Einsteinium (II) Chloride
  • EsCl3 Einsteinium (III) Chloride
  • EsF3 Einsteinium (III) Fluoride
  • EsI2 Einsteinium (II) Iodide
  • EsI3 Einsteinium (III) Iodide
  • Es2O3 einsteinium (III) Oxide

Today, einsteinium is produced though a lengthy chain of nuclear reactions that involves bombarding each isotope in the chain with neutrons and then allowing the resulting isotope to undergo beta decay.  Since only small amounts of einsteinium have ever been produced, it currently has no uses outside of basic scientific research.

2s2 2p6
3s2 3p6 3d10
4s2 4p6 4d10 4f14
5s2 5p6 5d10 5f11
6s2 6p6


19 radioisotopes of einsteinium have been characterized, with the most stable being 252Es with a half-life of 471.7 days, 254Es with the longest half-life of 275.7 days, 255Es with a half-life of 39.8 days, and 253Es with a half-life of 20.47 days.  All of the remaining radioactive isotopes have half-lifes that are less than 40 hours, and the majority of these have half lifes that are less than 30 minutes. This element also has 3 meta states, with the most stable being 254mEs (t 39.3 hours).  The isotopes of einsteinium range in atomic massfrom 240.069 u (240Es) to 258.100 u (258Es).

252Es decays into berkelium-248 through alpha decay, into californium-252 through electron capture or into fermium-252 through beta decay. 

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Atomic Mass
240Es 240.06892 ~1 seconds
241Es 241.06854 10 seconds
242Es 242.06975 13.5 seconds
243Es 243.06955 21 seconds
244Es 244.07088 37 seconds
245Es 245.07132 1.1 minutes
246Es 246.07290 7.7 minutes
247Es 247.07366 4.55 minutes
248Es 248.07547 27 minutes
249Es 249.07641 102.2 minutes
250Es 250.07861 8.6 hours
250mEs   2.22 hours
251Es 251.079992 33 hours
252Es 252.08298 471.7 days
253Es 253.0848247 20.47 days
254Es 254.088022 275.7 days
254mEs   39.3 hours
255Es 255.090273 39.8 days
256Es 256.09360 25.4 minutes
256mEs   7.6 hours
257Es 257.09598 7.7 days
258Es 258.09952 ~3 minutes


There is currently no evidence of einsteinium evolved in any biological role.  Due to its extreme rarity its only use is in scientific research.

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Einsteinium Data

Atomic Structure

  • Atomic Radius: ~860 pm
  • Atomic Volume:
  • Covalent Radius:
  • Cross Section (Thermal Neutron Capture) Barns: 160
  • Crystal Structure: Cubic face centered
  • Electron Configuration:
    1s2 2s2p6 3s2p6d10 4s2p6d10f14 5s2p6d10f11 6s2p6 7s2
  • Electrons per Energy Level: 2, 8, 18, 32, 29, 8, 2
  • Ionic Radius: 0.925
  • Filling Orbital: 5f11
  • Number of Electrons (with no charge): 99
  • Number of Neutrons (most common/stable nuclide): 153
  • Number of Protons: 99
  • Oxidation States: 3
  • Valence Electrons: 5f11 7s2

Chemical Properties

  • Electrochemical Equivalent: 4.74 g/amp-hr
  • Electron Work Function:
  • Electronegativity: 1.3 (Pauling); 1.2 (Allrod Rochow)
  • Heat of Fusion: kJ/mol
  • Incompatibilities:
  • Ionization Potential
    • First: 6.42
  • Valence Electron Potential (-eV):

Physical Properties

  • Atomic Mass Average: 252
  • Boiling Point:
  • Coefficient of Lineal Thermal Expansion/K-1: N/A
  • Conductivity
    Thermal: 0.1 W/cmoK
  • Description:
    Man made radioactive metal, which is not found in nature
  • Flammablity Class:
  • Freezing Point: see melting point
  • Heat of Vaporization: kJ/mol
  • Melting Point: 1133oK, 860C, 1580F
  • Physical State (at 20C & 1atm): Solid
  • Specific Heat:

Regulatory / Health

  • CAS Number
    • 7429-92-7
  • NFPA 704
    • Health:
    • Fire:
    • Reactivity:
    • Special Hazard: Radioactive<
    • OSHA Permissible Exposure Limit (PEL)
      • No limits set by OSHA
    • OSHA PEL Vacated 1989
      • No limits set by OSHA
    • NIOSH Recommended Exposure Limit (REL)
      • No limits set by NIOSH
    • Levels In Humans:
      Note: this data represents naturally occuring levels of elements in the typical human, it DOES NOT represent recommended daily allowances.
      • Blood/mg dm-3: N/A
      • Bone: N/A 
      • Liver: N/A 
      • Muscle: N/A 
      • Daily Dietary Intake: N/A
      • Total Mass In Avg. 70kg human: N/A

    Who / Where / When / How

    • Discoverer: G.R. Choppin, S.G. Thompson, A. Ghiorso and G.G. Harvey
    • Discovery Location: Berkeley California United States
    • Discovery Year: 1952
    • Name Origin:
      After the scientist Albert Einstein.
    • Abundance:
      • Earth's Crust:
      • Seawater:
      • Atmosphere:
      • Sun (Relative to H=1E12): N/A
    • Sources:
      Made by bombarding uranium with neutrons. World production is probably less than 1 gram per year.
    • Uses:
    • Additional Notes:
      In 1952 Einsteinium was discovered in the debris of a thermonuclear explosion test in the Pacific.