Einsteinium Facts: Element 99 or Es

Einsteinium Properties, Uses, Sources, and History

Einsteinium is a radioactive metal that glows in the dark.
Einsteinium is a radioactive metal that glows in the dark. Science Picture Co / Getty Images

 Einsteinium is a soft silver radioactive metal with atomic number 99 and element symbol Es. Its intense radioactivity makes it glow blue in the dark. The element is named in honor of Albert Einstein. 


Einsteinium was first identified in the fallout from the first hydrogen bomb explosion in 1952, the Ivy Mike nuclear test. Albert Ghiorso and his team at the University of California at Berkeley, together with Los Alamos and Argonne National Laboratories, detected and later synthesized Es-252, which exhibits a characteristic alpha decay with an energy of 6.6 MeV. The American team jokingly named element 99 "pandamonium" because the Ivy Mike test had been codenamed Project Panda, but the name they officially proposed was " einsteinium", with element symbol E. The IUPAC approved the name but went with the symbol Es.

The American team competed with a Swedish team at the Nobel Institute for Physics in Stockholm for credit discovering elements 99 and 100 and naming them. The Ivy Mike test had been classified. The American team published results in 1954, with the test results declassified in 1955. The Swedish team published results in 1953 and 1954.

Properties of Einsteinium

Einsteinium is a synthetic element, probably not found naturally. Primordial einsteinium (from when the Earth formed), if it existed, would have decayed by now. Successive neutron capture events from uranium and thorium could theoretically produce natural einsteinium. At present, the element is only produced in nuclear reactors or from nuclear weapon tests. It is made by bombarding other actinides with neutrons. Although not a lot of element 99 has been made, it is the highest atomic number produced in sufficient quantities to be seen in its pure form.

One problem studying einsteinium is that radioactivity of the element damages its crystal lattice. Another consideration is that einsteinium samples quickly become contaminated as the element decays into daughter nuclei. For example, Es-253 decays into Bk-249 and then Cf-249 at the rate of about 3% of the sample per day.

Chemically, einsteinium behaves much like other actinides, which are essentially radioactive transition metals. It's a reactive element that exhibits multiple oxidation states and forms colored compounds. The most stable oxidation state is +3, which is pale pink in aqueous solution. The +2 phase has been shown in a solid state, making it the first divalent actinide. The +4 state is predicted for the vapor phase but has not been observed. In addition to glowing in the dark from radioactivity, the element releases heat on the order of 1000 watts per gram. The metal is noteworthy for being paramagnetic.

All isotopes of einsteinium are radioactive. At least nineteen nuclides and three nuclear isomers are known. The isotopes range in atomic weight from 240 to 258. The most stable isotope is Es-252, which has a half-life of 471.7 days. Most isotopes decay within 30 minutes. One nuclear isomer of Es-254 has a half-life of 39.3 hours.

The uses of einsteinium are limited by the small quantities available and how quickly its isotopes decay. It is used for scientific research to learn about the element's properties and to synthesize other superheavy elements. For example, in 1955 einsteinium was used to produce the first sample of the element mendelevium.

Based on animal studies (rats), einsteinium is considered a toxic radioactive element. Over half of ingested Es is deposited in bones, where it remains for 50 years. A quarter goes to the lungs. A fraction of a percent goes to reproductive organs. About 10% is excreted.

Einsteinium Properties

Element Name: einsteinium

Element Symbol: Es

Atomic Number: 99

Atomic Weight: (252)

Discovery: Lawrence Berkeley National Lab (USA) 1952

Element Group: actinide, f-block element, transition metal

Element Period: period 7

Electron Configuration: [Rn] 5f11 7s2 (2, 8, 18, 32, 29, 8, 2)

Density (room temperature): 8.84 g/cm3

Phase: solid metal

Magnetic Order: paramagnetic

Melting Point: 1133 K  (860 °C, 1580 °F)

Boiling Point: 1269 K (996 °C, 1825 °F) predicted

Oxidation States: 2, 3, 4

Electronegativity: 1.3 on the Pauling scale

Ionization Energy: 1st: 619 kJ/mol

Crystal Structure: face-centered cubic (fcc)


Glenn T. Seaborg, The Transcalifornium Elements., Journal of Chemical Education, Vol 36.1 (1959) p 39.

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Helmenstine, Anne Marie, Ph.D. "Einsteinium Facts: Element 99 or Es." ThoughtCo, Aug. 1, 2021, thoughtco.com/einsteinium-facts-element-99-or-es-4126476. Helmenstine, Anne Marie, Ph.D. (2021, August 1). Einsteinium Facts: Element 99 or Es. Retrieved from https://www.thoughtco.com/einsteinium-facts-element-99-or-es-4126476 Helmenstine, Anne Marie, Ph.D. "Einsteinium Facts: Element 99 or Es." ThoughtCo. https://www.thoughtco.com/einsteinium-facts-element-99-or-es-4126476 (accessed June 7, 2023).