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99 californium ← einsteinium → fermium Ho ↑ Es ↓ (Uqe) Periodic Table - Extended Periodic Table
General
Name, Symbol, Number	einsteinium, Es, 99
Chemical series	actinides
Group, Period, Block	n/a, 7, f
Appearance	unknown, probably silvery white or metallic gray
Standard atomic weight	(252)  g·mol−1
Electron configuration	[Rn] 5f11 7s2
Electrons per shell	2, 8, 18, 32, 29, 8, 2
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
Miscellaneous
Magnetic ordering	no data
CAS registry number	7429-92-7
Selected 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 - -
References

Einsteinium (pronounced /aɪnˈstaɪniəm/) is a synthetic element. On the periodic table, it is represented by the symbol Es and atomic number 99. It is the seventh transuranic element, and seventh in the series of Actinides. It was named in honor of Albert Einstein.^[1]

Contents 1 Properties 2 Production 3 Uses 4 History 5 Isotopes 6 Known compounds 7 References 8 External links

Its position on the periodic table indicates that its chemical and physical properties are similar to other metals. Though only small amounts have ever 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 many of the synthetic elements, many of einsteinium's isotopes are radioactive.

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 aluminum and formed into pellets. The pellets are then further irradiated for approximately one year in a nuclear reactor. Another four months of irradition is required in a different reactor. The result is a mixture of californium and einsteinium, which can then be separated.^[2]

Aside from being the byproduct of creating other elements, or a step in the production of other elements, einsteinium has no known uses.^[3]

Einsteinium was first identified in December 1952 by Albert Ghiorso at the University of California, Berkeley.^[2] He was examining debris from the first hydrogen bomb test of November 1952 (see Operation Ivy).^[1] He 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 Cold War tensions.

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,^[4] with the most stable being ²⁵²Es with a half-life of 471.7 days, ²⁵⁴Es with a 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-lives that are less than 40 hours, and the majority of these have half-lives that are less than 30 minutes. This element also has three meta states, with the most stable being ^254mEs (t_½ 39.3 hours). The isotopes of einsteinium range in atomic mass from 240.069 u (²⁴⁰Es) to 258.100 u (²⁵⁸Es). The most original isotope is the ²⁵²Es.

The following is a list of all known compounds of einsteinium:^[5]

• 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

• Guide to the Elements - Revised Edition, Albert Stwertka, (Oxford University Press; 1998) ISBN 0-19-508083-1

• Los Alamos National Laboratory - Einsteinium
• It's Elemental - The Element Einsteinium
• WebElements.com - Einsteinium
• Albert Ghiorso about the discovery
• Einsteinium - Los Alamos National Laboratory