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General properties
Name, symbol, number einsteinium, Es, 99
Element category actinide
Group, period, block n/a7, f
Standard atomic weight (252)g·mol−1
Electron configuration [Rn] 5f11 7s2
Electrons per shell 2, 8, 18, 32, 29, 8, 2 (Image)
Physical properties
Phase solid
Density (near r.t.) 8.84 g·cm−3
Melting point 1133 K, 860 °C, 1580 °F
Atomic properties
Oxidation states 2, 3, 4
Electronegativity 1.3 (Pauling scale)
Ionization energies 1st: 619 kJ·mol−1
Magnetic ordering no data
CAS registry number 7429-92-7
Most stable isotopes
Main article: Isotopes of einsteinium
iso NA half-life DM DE (MeV) DP
252Es syn 471.7 d α 6.760 248Bk
ε 1.260 252Cf
β 0.480 252Fm
253Es syn 20.47 d SF - -
α 6.739 249Bk
254Es syn 275.7 d ε 0.654 254Cf
β 1.090 254Fm
α 6.628 250Bk
255Es syn 39.8 d β 0.288 255Fm
α 6.436 251Bk
SF - -

Einsteinium (pronounced /aɪnˈstaɪniəm/, eyen-STYE-nee-əm) is a metallic synthetic element. On the periodic table, it is represented by the symbol Es and atomic number 99. It is the seventh transuranic element, and an actinide. It was named in honor of Albert Einstein.[1]

Its position on the periodic table indicates that its chemical and physical properties are similar to other metals. Though only small amounts have been made, it has been determined to be silver-colored.[1] According to tracer studies conducted at Los Alamos National Laboratory using the isotope 253Es, this element has chemical properties typical of a heavy trivalent, actinide element.[2]

Like all synthetic elements, isotopes of einsteinium are extremely radioactive, and are considered highly toxic.



Einsteinium does not occur naturally in any measurable quantities. The modern process of creating the element starts with the irradiation of plutonium-239 in a nuclear reactor for several years. The resulting plutonium-242 isotope (in the form of the compound plutonium(IV) oxide) is mixed with aluminium and formed into pellets. The pellets are then further irradiated for approximately one year in a nuclear reactor. Another four months of irradiation is required in a different reactor. The result is a mixture of californium and einsteinium, which can then be separated.[2]


Aside from basic scientific research (such as being a step in the production of other elements[3]), einsteinium has no known uses.[4]


Einsteinium was first identified in December 1952 by Albert Ghiorso along with co-workers at the University of California, Berkeley.[2] He was examining debris from the first hydrogen bomb test of November 1952 (see Operation Ivy).[1][5] He discovered the isotope 253Es (half-life 20.5 days) that was made by the neutron capture of 15 neutrons with 238U (which then went through seven beta decays). These findings were kept secret until 1955 due to Cold War tensions.[6][7]

\mathrm{^{238}_{\ 94}U\ \xrightarrow [-7\ \beta^-]{+\ 15,\ 16,\ 17\ (n,\gamma)} \ ^{253,\ 254,\ 255}_{\ \ \ \ \ \ \ \ \ \ \ 99}Es}

Isotopes of einsteinium were produced shortly afterward at the University of California Radiation Laboratory in a nuclear fusion reaction between 14N and 238U[8] and later by intense neutron irradiation of plutonium in the Materials Testing Reactor.[9]

In 1961, enough einsteinium was synthesized to prepare a microscopic amount of 253Es. This sample weighed about 0.01 mg and was measured using a special balance. The material produced was used to produce mendelevium. Further einsteinium has been produced at the Oak Ridge National Laboratory's High Flux Isotope Reactor in Tennessee by bombarding 239Pu with neutrons. Around 3 milligrams were created over a four year program of irradiation and then chemical separation from a starting 1 kg of plutonium isotope.


Nineteen radioisotopes of einsteinium have been characterized,[10] with the most stable being 252Es with a half-life of 471.7 days. 254Es has a half-life of 275.7 days, 255Es 39.8 days and 253Es 20.47 days. All of the remaining radioactive isotopes have half-lives that are less than 40 hours, the majority of these having half-lives that are less than 30 minutes. This element also has three meta states, with the most stable being 254mEs (t½ 39.3 hours). The isotopes of einsteinium range in atomic mass from 240.069 u (240Es) to 258.100 u (258Es). The longest-lived isotope is 252Es.

Known compounds

Einsteinium iodide EsI3 in transmitted light

The following is a list of all known compounds of einsteinium:[11]

  • 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


  1. ^ a b c d Einsteinium - National Research Council Canada. Retrieved 2 December 2007.
  2. ^ a b c Einsteinium - Los Alamos National Laboratory. Retrieved 2 December 2007.
  3. ^ See Mendelevium#History
  4. ^ It's Elemental - The Element Einsteinium. Retrieved 2 December 2007.
  5. ^ Albert Ghiorso (2003). "Einsteinium and Fermium". Chemical and Engineering News. 
  6. ^ Ghiorso, A. and Thompson, S. G. and Higgins, G. H. and Seaborg, G. T. and Studier, M. H. and Fields, P. R. and Fried, S. M. and Diamond, H. and Mech, J. F. and Pyle, G. L. and Huizenga, J. R. and Hirsch, A. and Manning, W. M. and Browne, C. I. and Smith, H. L. and Spence, R. W. (1955). "New Elements Einsteinium and Fermium, Atomic Numbers 99 and 100". Phys. Rev. 99: 1048–1049. doi:10.1103/PhysRev.99.1048. 
  7. ^ P. R. Fields, M. H. Studier, H. Diamond, J. F. Mech, M. G. Inghram, G. L. Pyle, C. M. Stevens, S. Fried, W. M. Manning (Argonne National Laboratory, Lemont, Illinois); A. Ghiorso, S. G. Thompson, G. H. Higgins, G. T. Seaborg (University of California, Berkeley, California): "Transplutonium Elements in Thermonuclear Test Debris", in: Physical Review 1956, 102 (1), 180–182; doi:10.1103/PhysRev.102.180.
  8. ^ Ghiorso, Albert and Rossi, G. Bernard and Harvey, Bernard G. and Thompson, Stanley G. (1954). "Reactions of U-238 with Cyclotron-Produced Nitrogen Ions". Physical Review 93: 257. doi:10.1103/PhysRev.93.257. 
  9. ^ Thompson, S. G. and Ghiorso, A. and Harvey, B. G. and Choppin, G. R. (1954). "Transcurium Isotopes Produced in the Neutron Irradiation of Plutonium". Physical Review 93: 908. doi:10.1103/PhysRev.93.908. 
  10. ^ Table of Isotopes decay data - LBNL Isotopes Project - LUNDS Universitet. Retrieved 25 November 2007.
  11. ^ Chemistry : Periodic Table : einsteinium : compounds information - WebElements. Retrieved 29 December 2008.


  • Stwertka, Albert (1996). A Guide to the Elements. Oxford Oxfordshire: Oxford University Press. ISBN 0195080831. 

External links



Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

See also einsteinium


Chemical Element: Es (atomic number 99)


Einsteinium n

  1. einsteinium

Simple English

Einsteinium is a chemical element with the atomic number 99. That means an Einsteinium atom consists of 99 protons, 100 or more neutrons and 99 electrons. It is a synthetic element, all isotopes are radioactive.

Einsteinium belongs to the actinoids, and it is the 7th of them. The most stable isotope of Einsteinium consists of 99 protons and electrons and 153 neutrons. There are 19 different (radioactive) isotopes. Einsteinium is named after Albert Einstein. It was found first time in 1952 by Albert Ghiorso at the University of California, Berkeley.

Einsteinium istopes have a half-life between 40 and 471 days.


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