|Name, Symbol, Number||einsteinium, Es, 99|
|Group, Period, Block||n/a, 7, f|
|Appearance||unknown, probably silvery
white or metallic gray
|Atomic mass||(252) g/mol|
|Electron configuration||[Rn] 5f11 7s2|
|Electrons per shell||2, 8, 18, 32, 29, 8, 2|
|Density (near r.t.)||8.84 g/cm³|
|Melting point||1133 K
(860 °C, 1580 °F)
|Oxidation states||2, 3, 4|
|Electronegativity||1.3 (Pauling scale)|
|Ionization energies||1st: 619 kJ/mol|
|Magnetic ordering||no data|
|CAS registry number||7429-92-7|
Einsteinium (chemical symbol Es, atomic number 99) is a synthetic element in the periodic table. A metallic, highly radioactive, transuranic element (seventh in the series) in the actinides, einsteinium is produced by bombarding plutonium with neutrons and was discovered in the debris of the first hydrogen bomb test. It is of interest mainly for scientific research, and practical applications of the element have yet to be developed.
Einsteinium was named after Albert Einstein. 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 hydrogen bomb test of November 1952 (see 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 Cold War tensions, however.
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 three mg was created over a four year program of irradiation and then chemical separation from a starting one kg of plutonium isotope.
Einsteinium is an inner transition metal of the actinide series, located in period seven of the periodic table, between californium and fermium. Tracer studies using the isotope 253Es show that einsteinium has chemical properties typical of a heavy trivalent, actinide element.
19 radioisotopes of einsteinium have been characterized, 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 (t½ 39.3 hours). The isotopes of einsteinium range in atomic mass from 240.069 amu (240Es) to 258.100 amu (258Es).
Known compounds of einsteinium include the following:
All links retrieved September 15, 2013.
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