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{{infobox einsteinium}}
'''Einsteinium''' is a [[synthetic element|synthetic chemical element]]; it has [[Chemical symbol|symbol]] '''Es''' and [[atomic number]] 99 and is a member of the [[actinide]] series and the seventh [[transuranium element]]. 

Einsteinium was discovered as a component of the debris of the [[Ivy Mike|first hydrogen bomb]] explosion in 1952. Its most common [[isotope]], einsteinium-253 ({{sup|253}}Es; [[half-life]] 20.47 days), is produced artificially from decay of [[californium]]-253 in a few dedicated high-power [[nuclear reactor]]s with a total yield on the order of one milligram per year. The reactor synthesis is followed by a complex process of separating einsteinium-253 from other actinides and products of their decay. Other isotopes are synthesized in various laboratories, but in much smaller amounts, by bombarding heavy actinide elements with light ions. Due to the small amounts of einsteinium produced and the short half-life of its most common isotope, there are no practical applications for it except basic scientific research. In particular, einsteinium was used to synthesize, for the first time, 17 atoms of the new element [[mendelevium]] in 1955.

Einsteinium is a soft, silvery, [[paramagnetic]] metal. Its chemistry is typical of the late actinides, with a preponderance of the +3 [[oxidation state]]; the +2 oxidation state is also accessible, especially in solids. The high radioactivity of {{sup|253}}Es produces a visible glow and rapidly damages its crystalline metal lattice, with released heat of about 1,000 [[watt]]s per gram. Studying its properties is difficult due to {{sup|253}}Es's decay to [[berkelium]]-249 and then californium-249 at a rate of about 3% per day. The longest-lived isotope of einsteinium, {{sup|252}}Es (half-life 471.7 days) would be more suitable for investigation of physical properties, but it has proven far more difficult to produce and is available only in minute quantities, not in bulk.<ref>[https://periodic.lanl.gov/99.shtml Einsteinium] {{Webarchive|url=https://web.archive.org/web/20210519093827/https://periodic.lanl.gov/99.shtml |date=2021-05-19 }}. periodic.lanl.gov</ref> Einsteinium is the element with the highest atomic number which has been observed in macroscopic quantities in its pure form as einsteinium-253.<ref name="h1579"/>

Like all synthetic transuranium elements, isotopes of einsteinium are very [[radioactive decay|radioactive]] and are considered highly dangerous to health on ingestion.<ref name="CRC"/>

==History==
[[File:Ivy Mike - mushroom cloud.jpg|thumb|left|Einsteinium was first observed in the fallout from the ''Ivy Mike'' nuclear test.]]
Einsteinium was [[timeline of chemical element discoveries|first identified]] in December 1952 by [[Albert Ghiorso]] and co-workers at [[University of California, Berkeley]] in collaboration with the [[Argonne National Laboratory|Argonne]] and [[Los Alamos National Laboratory|Los Alamos]] National Laboratories, in the fallout from the ''[[Ivy Mike]]'' nuclear test. The test was done on November 1, 1952, at [[Enewetak Atoll]] in the [[Pacific Ocean]] and was the first successful test of a [[thermonuclear weapon]].<ref name="Ghiorso"/> Initial examination of the debris from the explosion had shown the production of a new isotope of [[plutonium]], <sup>244</sup>Pu, which could only have formed by the absorption of six [[neutron]]s by a [[uranium-238]] nucleus followed by two [[beta decay]]s.
:<chem>^{238}_{92}U ->[\ce{+ 6(n,\gamma)}][-2\ \beta^-]{} ^{244}_{94}Pu</chem>
At the time, the multiple neutron absorption was thought to be an extremely rare process, but the identification of {{sup|244}}Pu indicated that still more neutrons could have been captured by the uranium, producing new elements heavier than [[californium]].<ref name="Ghiorso">{{cite journal|first = Albert|last = Ghiorso|author-link = Albert Ghiorso|date = 2003|title = Einsteinium and Fermium|journal = Chemical and Engineering News|url = http://pubs.acs.org/cen/80th/einsteiniumfermium.html|volume = 81|issue = 36|doi = 10.1021/cen-v081n036.p174|pages = 174–175|access-date = 2007-04-15|archive-date = 2018-09-06|archive-url = https://web.archive.org/web/20180906064329/http://pubs.acs.org/cen/80th/einsteiniumfermium.html|url-status = live|url-access = subscription}}</ref>

[[File:Albert Ghiorso ca 1970.jpg|thumb|left|upright|The element was discovered by a team headed by [[Albert Ghiorso]].]]
Ghiorso and co-workers analyzed filter papers which had been flown through the explosion cloud on airplanes (the same sampling technique that had been used to discover {{sup|244}}Pu).<ref name="s39">[[#Seaborg|Seaborg]], p. 39</ref> Larger amounts of radioactive material were later isolated from coral debris of the atoll, and these were delivered to the U.S.<ref name="Ghiorso"/> The separation of suspected new elements was carried out in the presence of a [[citric acid]]/[[ammonium]] [[buffer solution]] in a weakly acidic medium ([[pH]] ≈ 3.5), using [[ion exchange]] at elevated temperatures; fewer than 200 atoms of einsteinium were recovered in the end.<ref name="em">{{cite book|last=Emsley|url=https://books.google.com/books?id=j-Xu07p3cKwC&pg=PA133|title=Nature's building blocks: an A-Z guide to the elements|archive-url=https://web.archive.org/web/20160609222635/https://books.google.com/books?id=j-Xu07p3cKwC&pg=PA133|archive-date=2016-06-09|publisher=Oxford University Press|year=2003|isbn=0-19-850340-7|pages=133–135|first=John}}</ref> Nevertheless, element 99, einsteinium, and in particular {{sup|253}}Es, could be detected via its characteristic high-energy [[alpha decay]] at 6.6&nbsp;MeV.<ref name = "Ghiorso"/> It was produced by the [[neutron capture|capture]] of 15 [[neutron]]s by [[uranium-238]] nuclei followed by seven beta decays, and had a [[half-life]] of 20.5 days. Such multiple neutron absorption was made possible by the high neutron flux density during the detonation, so that newly generated heavy isotopes had plenty of available neutrons to absorb before they could disintegrate into lighter elements. Neutron capture initially raised the [[mass number]] without changing the [[atomic number]] of the nuclide, and the concomitant beta-decays resulted in a gradual increase in the atomic number:<ref name="Ghiorso"/>
:<chem>
^{238}_{92}U ->[\ce{+15n}][6 \beta^-] ^{253}_{98}Cf ->[\beta^-] ^{253}_{99}Es
</chem>

Some {{sup|238}}U atoms, however, could absorb two additional neutrons (for a total of 17), resulting in {{sup|255}}Es, as well as in the {{sup|255}}Fm isotope of another new element, [[fermium]].<ref>{{sup|254}}Es, {{sup|254}}Fm and {{sup|253}}Fm would not be produced because of lack of beta decay in {{sup|254}}Cf and {{sup|253}}Es.</ref> The discovery of the new elements and the associated new data on multiple neutron capture were initially kept secret on the orders of the U.S. military until 1955 due to [[Cold War]] tensions and competition with Soviet Union in nuclear technologies.<ref name="Ghiorso"/><ref name = "ES_FM">{{cite journal|last1 = Ghiorso|first1 = A.|last2 = Thompson|first2 = S.|last3 = Higgins|first3 = G.|last4 = Seaborg|first4 = G.|last5 = Studier|first5 = M.|last6 = Fields|first6 = P.|last7 = Fried|first7 = S.|last8 = Diamond|first8 = H.|last9 = Mech|first9 = J.|first10 = G.|last10 = Pyle|first11 = J.|last11 = Huizenga|first12 = A.|last12 = Hirsch|first13 = W.|last13 = Manning|first14 = C.|last14 = Browne|first15 = H.|last15 = Smith|first16 = R.|last16 = Spence|title = New Elements Einsteinium and Fermium, Atomic Numbers 99 and 100|journal = Phys. Rev.|volume = 99|issue = 3|url = http://escholarship.org/uc/item/70q401ct|doi = 10.1103/PhysRev.99.1048|pages = 1048–1049|date = 1955|bibcode = 1955PhRv...99.1048G|access-date = 2010-11-24|archive-date = 2021-05-19|archive-url = https://web.archive.org/web/20210519093844/https://escholarship.org/uc/item/70q401ct|url-status = live|doi-access = free}} {{citation|url=https://books.google.com/books?id=e53sNAOXrdMC&pg=PA91|title=Modern Alchemy: Selected Papers of Glenn T. Seaborg|isbn=9789810214401 |archive-url=https://web.archive.org/web/20160413022543/https://books.google.com/books?id=e53sNAOXrdMC&pg=PA91|archive-date=2016-04-13 |last1=Seaborg |first1=Glenn Theodore |year=1994 |publisher=World Scientific }}</ref><ref>{{cite journal|last1=Fields|first1=P.|last2=Studier|first2=M.|last3=Diamond|first3=H.|last4=Mech|first4=J.|last5=Inghram|first5=M.|last6=Pyle|first6=G.|last7=Stevens|first7=C.|last8=Fried|first8=S.|last9=Manning|first9=W. |first10 = G. |last10 = Pyle |first11 = J. |last11 = Huizenga |first12 = A. |last12 = Hirsch |first13 = W. |last13 = Manning |first14 = C. |last14 = Browne |first15 = H. |last15 = Smith |first16 = R. |last16 = Spence |title=Transplutonium Elements in Thermonuclear Test Debris|journal=Physical Review |volume=102|issue=1|date=1956|pages=180–182|doi=10.1103/PhysRev.102.180|bibcode = 1956PhRv..102..180F|isbn=978-981-02-1440-1 |url=https://books.google.com/books?id=e53sNAOXrdMC&pg=PA93|via=Google Books|archive-url=https://web.archive.org/web/20160423081455/https://books.google.com/books?id=e53sNAOXrdMC&pg=PA93|archive-date=2016-04-23 |url-access=subscription}}</ref> However, the rapid capture of so many neutrons would provide needed direct experimental confirmation <!--"convincing evidence of the reality of"--> of the [[r-process]] multi-neutron absorption needed to explain the cosmic [[nucleosynthesis]] (production) of certain heavy elements (heavier than nickel) in [[supernova]]s, before [[beta decay]]. Such a process is needed to explain the existence of many stable elements in the universe.<ref>{{cite book|last=Byrne, J.|title=Neutrons, Nuclei, and Matter|publisher=Dover Publications|location=Mineola, NY|year=2011|isbn=978-0-486-48238-5}} (pbk.) pp. 267.</ref>

Meanwhile, isotopes of element 99 (as well as of new element 100, [[fermium]]) were produced in the Berkeley and Argonne laboratories, in a [[nuclear fusion|nuclear reaction]] between [[nitrogen]]-14 and uranium-238,<ref name = "PhysRev.93.257">{{cite journal| journal = Physical Review| volume = 93|issue = 1| date = 1954|title = Reactions of U-238 with Cyclotron-Produced Nitrogen Ions| author = Ghiorso, Albert| author2 = Rossi, G. Bernard| author3 = Harvey, Bernard G.| author4 = Thompson, Stanley G.| s2cid = 121499772| name-list-style = amp| doi = 10.1103/PhysRev.93.257|pages = 257|bibcode = 1954PhRv...93..257G }}</ref> and later by intense neutron irradiation of [[plutonium]] or [[californium]]:
:<chem>^{252}_{98}Cf ->[\ce{(n,\gamma)}] ^{253}_{98}Cf ->[\beta^-][17.81 \ce{d}] ^{253}_{99}Es ->[\ce{(n,\gamma)}] ^{254}_{99}Es ->[\beta^-] ^{254}_{100}Fm</chem>

These results were published in several articles in 1954 with the disclaimer that these were not the first studies that had been carried out on the elements.<ref name = "PhysRev.93.908" >{{cite journal| journal = Physical Review| volume = 93| date = 1954| title = Transcurium Isotopes Produced in the Neutron Irradiation of Plutonium| author = Thompson, S. G.| author2 = Ghiorso, A.| author3 = Harvey, B. G.| author4 = Choppin, G. R.| doi = 10.1103/PhysRev.93.908| pages = 908| issue = 4| bibcode = 1954PhRv...93..908T| url = https://digital.library.unt.edu/ark:/67531/metadc1016991/| access-date = 2019-07-14| archive-date = 2020-03-16| archive-url = https://web.archive.org/web/20200316232939/https://digital.library.unt.edu/ark:/67531/metadc1016991/| url-status = live| doi-access = free}}</ref><ref>{{cite journal|last1=Harvey|first1=Bernard|last2=Thompson|first2=Stanley|last3=Ghiorso|first3=Albert|last4=Choppin|first4=Gregory|title=Further Production of Transcurium Nuclides by Neutron Irradiation|journal=Physical Review|volume=93|pages=1129|date=1954|doi=10.1103/PhysRev.93.1129|issue=5|bibcode=1954PhRv...93.1129H|url=http://www.escholarship.org/uc/item/7884m0gv|access-date=2019-07-14|archive-date=2020-03-09|archive-url=https://web.archive.org/web/20200309181708/https://escholarship.org/uc/item/7884m0gv|url-status=live}}</ref><ref>{{cite journal|last1=Studier|first1=M.|last2=Fields|first2=P.|last3=Diamond|first3=H.|last4=Mech|first4=J.|last5=Friedman|first5=A.|last6=Sellers|first6=P.|last7=Pyle|first7=G.|last8=Stevens|first8=C.|last9=Magnusson|first9=L.|first10=J.|last10=Huizenga |title=Elements 99 and 100 from Pile-Irradiated Plutonium|journal=Physical Review|volume=93|pages=1428|date=1954|doi=10.1103/PhysRev.93.1428|issue=6|bibcode = 1954PhRv...93.1428S }}</ref><ref>{{cite journal|first1 = G. R.|last1 = Choppin|first2 = S. G.|last2 = Thompson|first3 = A.|last3 = Ghiorso|author-link3 = Albert Ghiorso|first4 = B. G.|last4 = Harvey|title = Nuclear Properties of Some Isotopes of Californium, Elements 99 and 100|journal = Physical Review|volume = 94|issue = 4|pages = 1080–1081|date = 1954|doi = 10.1103/PhysRev.94.1080|bibcode = 1954PhRv...94.1080C |doi-access = free}}</ref><ref>{{cite journal|last1=Fields|first1=P.|last2=Studier|first2=M.|last3=Mech|first3=J.|last4=Diamond|first4=H.|last5=Friedman|first5=A.|last6=Magnusson|first6=L.|last7=Huizenga|first7=J.|title=Additional Properties of Isotopes of Elements 99 and 100|journal=Physical Review|volume=94|issue=1|pages=209–210|date=1954|doi=10.1103/PhysRev.94.209|bibcode = 1954PhRv...94..209F }}</ref> The Berkeley team also reported some results on the chemical properties of einsteinium and fermium.<ref name="Properties_1">{{citation|last=Seaborg, G. T.; Thompson, S.G.; Harvey, B.G. and Choppin, G.R.|date=July 23, 1954|url=http://www.osti.gov/accomplishments/documents/fullText/ACC0047.pdf|title=Chemical Properties of Elements 99 and 100|journal=Journal of the American Chemical Society |volume=76 |issue=24 |page=6229 |doi=10.1021/ja01653a004 |bibcode=1954JAChS..76.6229T |archive-url=https://web.archive.org/web/20190710170811/http://www.osti.gov/accomplishments/documents/fullText/ACC0047.pdf|archive-date=2019-07-10}} Radiation Laboratory, University of California, Berkeley, UCRL-2591</ref><ref name="Properties_2">{{cite journal|title=Chemical Properties of Elements 99 and 100|last1=Thompson|first1=S. G.|last2=Harvey|first2=B. G.|last3=Choppin|first3=G. R.|last4=Seaborg|first4=G. T.|journal=Journal of the American Chemical Society|volume=76|pages=6229–6236|date=1954|doi=10.1021/ja01653a004|issue=24|bibcode=1954JAChS..76.6229T |url=https://digital.library.unt.edu/ark:/67531/metadc1023183/|access-date=2019-07-14|archive-date=2019-10-20|archive-url=https://web.archive.org/web/20191020212317/https://digital.library.unt.edu/ark:/67531/metadc1023183/|url-status=live}}</ref> The ''Ivy Mike'' results were declassified and published in 1955.<ref name = "ES_FM"/>

[[File:Einstein1921 by F Schmutzer 2.jpg|thumb|right|upright|The element was named after [[Albert Einstein]].]]
In their discovery of elements 99 and 100, the American teams had competed with a group at the Nobel Institute for Physics, [[Stockholm]], [[Sweden]]. In late 1953 to early 1954, the Swedish group succeeded in synthesizing light isotopes of element 100, in particular {{sup|250}}Fm, by bombarding uranium with oxygen nuclei. These results were also published in 1954.<ref>{{cite journal|last1=Atterling|first1=Hugo|last2=Forsling|first2=Wilhelm|last3=Holm|first3=Lennart|last4=Melander|first4=Lars|last5=Åström|first5=Björn|title=Element 100 Produced by Means of Cyclotron-Accelerated Oxygen Ions|journal=Physical Review|volume=95|pages=585–586|date=1954|doi=10.1103/PhysRev.95.585.2|issue=2|bibcode = 1954PhRv...95..585A }}</ref> Nevertheless, the priority of the Berkeley team was generally recognized, as its publications preceded the Swedish article, and they were based on the previously undisclosed results of the 1952 thermonuclear explosion; thus the Berkeley team was given the privilege to name the new elements. As the effort which had led to the design of ''Ivy Mike'' was codenamed Project PANDA,<ref name="underthecloud">{{cite book |title=Under the cloud: the decades of nuclear testing |last=Miller |page=115 |isbn=978-1-881043-05-8 |publisher=Two-Sixty Press |date=1991|first=Richard Lee}}</ref> element 99 had been jokingly nicknamed "Pandemonium"<!-- sic: /not/ pandemonium --><ref name="mcphee">{{cite book |title=The Curve of Binding Energy |first=John |last=McPhee |author-link=John McPhee |page=116 |publisher=Farrar, Straus & Giroux Inc. |isbn=978-0-374-51598-0 |date=1980}}</ref> but the official names suggested by the Berkeley group derived from two prominent scientists, Einstein and Fermi: "We suggest for the name for the element with the atomic number 99, einsteinium (symbol E) after [[Albert Einstein]] and for the name for the element with atomic number 100, fermium (symbol Fm), after [[Enrico Fermi]]."<ref name = "ES_FM "/> Both Einstein and Fermi died between the time the names were originally proposed and when they were announced. The discovery of these new elements was announced by [[Albert Ghiorso]] at the first Geneva Atomic Conference held on 8–20 August 1955.<ref name="Ghiorso"/> The symbol for einsteinium was first given as "E" and later changed to "Es" by IUPAC.<ref name="h1577">[[#Haire|Haire]], p. 1577</ref><ref name="se6">{{cite book|last=Seaborg, G.T.|year=1994|url=https://books.google.com/books?id=e53sNAOXrdMC&pg=PA6|title=Modern alchemy: selected papers of Glenn T. Seaborg|archive-url=https://web.archive.org/web/20160609194723/https://books.google.com/books?id=e53sNAOXrdMC&pg=PA6|archive-date=2016-06-09|publisher=World Scientific|page=6|isbn=981-02-1440-5}}</ref>

==Characteristics==

===Physical===
[[File:EinsteiniumGlow.JPG|thumb|left|upright|Glow due to the intense radiation from ~300 μg of {{sup|253}}Es<ref>[[#Haire|Haire]], p. 1580</ref>]]
Einsteinium is a synthetic, silvery, radioactive metal. In the [[periodic table]], it is located to the right of the actinide [[californium]], to the left of the actinide [[fermium]] and below the lanthanide [[holmium]] with which it shares many similarities in physical and chemical properties. Its density of 8.84&nbsp;g/cm{{sup|3}} is lower than that of californium (15.1&nbsp;g/cm{{sup|3}}) and is nearly the same as that of holmium (8.79&nbsp;g/cm{{sup|3}}), despite einsteinium being much heavier per atom than holmium. Einsteinium's melting point (860&nbsp;°C) is also relatively low—below californium (900&nbsp;°C), fermium (1,527&nbsp;°C) and holmium (1,461&nbsp;°C).<ref name="CRC">Hammond C. R. "The elements" in {{RubberBible86th}}</ref><ref name="HAIRE_1990">Haire, R. G. (1990) "Properties of the Transplutonium Metals (Am-Fm)", in: Metals Handbook, Vol.&nbsp;2, 10th edition, (ASM International, Materials Park, Ohio), pp. 1198–1201.</ref> Einsteinium is a soft metal, with a [[bulk modulus]] of only 15&nbsp;GPa, one of the lowest among non-[[alkali metal]]s.<ref name="h1591">[[#Haire|Haire]], p. 1591</ref>

Unlike the lighter actinides [[californium]], [[berkelium]], [[curium]] and [[americium]], which crystallize in a double [[hexagonal crystal family|hexagonal]] structure at ambient conditions; einsteinium is believed to have a [[Cubic crystal system|face-centered cubic]] (''fcc'') symmetry with the space group ''Fm''{{overline|3}}''m'' and the lattice constant {{nowrap|''a'' {{=}} 575&nbsp;pm}}. However, there is a report of room-temperature hexagonal einsteinium metal with {{nowrap|''a'' {{=}} 398 pm}} and {{nowrap|''c'' {{=}} 650 pm}}, which converted to the ''fcc'' phase upon heating to 300&nbsp;°C.<ref name="ev"/>

The self-damage induced by the radioactivity of einsteinium is so strong that it rapidly destroys the crystal lattice,<ref name="g1268"/> and the energy release during this process, 1000 watts per gram of <sup>253</sup>Es, induces a visible glow.<ref name="h1579">[[#Haire|Haire]], p. 1579</ref> These processes may contribute to the relatively low density and melting point of einsteinium.<ref name="ES_METALL">{{cite journal|last1=Haire|first1=R. G.|last2=Baybarz|first2=R. D.|doi=10.1051/jphyscol:1979431|title=Studies of einsteinium metal|date=1979|pages=C4–101|volume=40|journal=Le Journal de Physique|s2cid=98493620 |url=http://hal.archives-ouvertes.fr/docs/00/21/88/27/PDF/ajp-jphyscol197940C431.pdf|access-date=2010-11-24|archive-date=2012-03-07|archive-url=https://web.archive.org/web/20120307233020/http://hal.archives-ouvertes.fr/docs/00/21/88/27/PDF/ajp-jphyscol197940C431.pdf|url-status=live}} [http://www.osti.gov/bridge/servlets/purl/6582609-SrTVod/6582609.pdf draft manuscript] {{Webarchive|url=https://web.archive.org/web/20190710170812/http://www.osti.gov/bridge/servlets/purl/6582609-SrTVod/6582609.pdf |date=2019-07-10 }}</ref> Further, due to the small size of available samples, the melting point of einsteinium was often deduced by observing the sample being heated inside an electron microscope.<ref name="s61">[[#Seaborg|Seaborg]], p. 61</ref> Thus, surface effects in small samples could reduce the melting point.

The metal is trivalent and has a noticeably high volatility.<ref>{{cite journal|last1=Kleinschmidt|first1=Phillip D.|last2=Ward|first2=John W.|last3=Matlack|first3=George M.|last4=Haire|first4=Richard G.|title=Henry's Law vaporization studies and thermodynamics of einsteinium-253 metal dissolved in ytterbium|journal=The Journal of Chemical Physics|volume=81|issue=1|pages=473–477|date=1984|doi=10.1063/1.447328|bibcode = 1984JChPh..81..473K }}</ref> In order to reduce the self-radiation damage, most measurements of solid einsteinium and its compounds are performed right after thermal annealing.<ref name="s52">[[#Seaborg|Seaborg]], p. 52</ref> Also, some compounds are studied under the atmosphere of the reductant gas, for example H{{sub|2}}O+[[hydrogen chloride|HCl]] for EsOCl so that the sample is partly regrown during its decomposition.<ref name="s60"/>

Apart from the self-destruction of solid einsteinium and its compounds, other intrinsic difficulties in studying this element include scarcity—the most common {{sup|253}}Es isotope is available only once or twice a year in sub-milligram amounts—and self-contamination due to rapid conversion of einsteinium to berkelium and then to californium at a rate of about 3.3% per day:<ref name="ES_F3"/><ref name="ES2O3"/><ref name="s55">[[#Seaborg|Seaborg]], p. 55</ref>
:<chem>
^{253}_{99}Es ->[\alpha][20 \ce{d}] ^{249}_{97}Bk ->[\beta^-][314 \ce{d}] ^{249}_{98}Cf
</chem>

Thus, most einsteinium samples are contaminated, and their intrinsic properties are often deduced by extrapolating back experimental data accumulated over time. Other experimental techniques to circumvent the contamination problem include selective optical excitation of einsteinium ions by a tunable laser, such as in studying its luminescence properties.<ref name="s76">[[#Seaborg|Seaborg]], p. 76</ref>

Magnetic properties have been studied for einsteinium metal, its oxide and fluoride. All three materials showed [[Curie–Weiss law|Curie–Weiss]] [[paramagnetic]] behavior from [[liquid helium]] to room temperature. The effective magnetic moments were deduced as {{val|10.4|0.3|u=[[Bohr magneton|''μ''{{sub|B}}]]}} for Es{{sub|2}}O{{sub|3}} and {{val|11.4|0.3|u=''μ''{{sub|B}}}} for the EsF{{sub|3}}, which are the highest values among actinides, and the corresponding [[Curie temperature]]s are 53 and 37 K.<ref>{{cite journal|last1=Huray|first1=P.|last2=Nave|first2=S.|last3=Haire|first3=R.|title=Magnetism of the heavy 5f elements|journal=Journal of the Less Common Metals|volume=93|pages=293–300|date=1983|doi=10.1016/0022-5088(83)90175-3|issue=2}}</ref><ref>{{cite journal|last1=Huray|first1=Paul G.|last2=Nave|first2=S. E.|last3=Haire|first3=R. G.|last4=Moore|first4=J. R.|title=Magnetic Properties of Es{{sub|2}}O{{sub|3}} and EsF{{sub|3}}|journal=Inorganica Chimica Acta|volume=94|issue=1–3|pages=120–122|date=1984|doi=10.1016/S0020-1693(00)94587-0}}</ref>

===Chemical===
Like all actinides, einsteinium is rather reactive. Its trivalent [[oxidation state]] is most stable in solids and aqueous solution where it induces a pale pink color.<ref name="HOWI_1956">[[#Holleman|Holleman]], p. 1956</ref> The existence of divalent einsteinium is firmly established, especially in the solid phase; such +2 state is not observed in many other actinides, including [[protactinium]], [[uranium]], [[neptunium]], [[plutonium]], [[curium]] and [[berkelium]]. Einsteinium(II) compounds can be obtained, for example, by reducing einsteinium(III) with [[samarium(II) chloride]].<ref name="s53">[[#Seaborg|Seaborg]], p. 53</ref>

===Isotopes===
{{main|Isotopes of einsteinium}}
Eighteen isotopes and four [[nuclear isomer]]s are known for einsteinium, with [[mass number]]s 240–257.{{NUBASE2020|ref}} All are radioactive; the most stable one, {{sup|252}}Es, has half-life 471.7 days.<ref>{{cite journal|last1=Ahmad|first1=I.|title=Half-life of the longest-lived einsteinium isotope-252Es|journal=Journal of Inorganic and Nuclear Chemistry|volume=39|pages=1509–1511|date=1977|doi=10.1016/0022-1902(77)80089-4|issue=9|last2=Wagner|first2=Frank}}</ref> The next most stable isotopes are {{sup|254}}Es (half-life 275.7 days),<ref>{{cite journal|last1=McHarris|first1=William|last2=Stephens|first2=F.|last3=Asaro|first3=F.|last4=Perlman|first4=I.|title=Decay Scheme of Einsteinium-254|journal=Physical Review|volume=144|pages=1031–1045|date=1966|doi=10.1103/PhysRev.144.1031|issue=3|bibcode = 1966PhRv..144.1031M }}</ref> {{sup|255}}Es (39.8 days), and {{sup|253}}Es (20.47 days). All the other isotopes have half-lives shorter than 40 hours, most shorter than 30 minutes. Of the five isomers, the most stable is {{sup|254m}}Es with a half-life of 39.3 hours.{{NUBASE2020|ref}}

===Nuclear fission===
Einsteinium has a high rate of [[nuclear fission]] that results in a low [[critical mass]]. This mass is 9.89 kilograms for a bare sphere of {{sup|254}}Es, and can be lowered to 2.9 kg by adding a 30-centimeter-thick steel [[neutron reflector]], or even to 2.26 kg with a 20-cm-thick reflector made of water. However, even this small critical mass far exceeds the total amount of einsteinium isolated so far, especially of the rare {{sup|254}}Es.<ref name="irsn">Institut de Radioprotection et de Sûreté Nucléaire, [https://ec.europa.eu/energy/sites/ener/files/documents/20131018_trm_evaluation.pdf "Evaluation of nuclear criticality safety data and limits for actinides in transport"] {{Webarchive|url=https://web.archive.org/web/20160306031803/http://ec.europa.eu/energy/sites/ener/files/documents/20131018_trm_evaluation.pdf |date=2016-03-06 }}, p. 16.</ref>

===Natural occurrence===
Due to the short half-life of all isotopes of einsteinium, any [[Primordial nuclide|primordial]] einsteinium—that is, einsteinium that could have been present on Earth at its formation—has long since decayed. Synthesis of einsteinium from naturally occurring uranium and thorium in the Earth's crust requires multiple neutron capture, an extremely unlikely event. Therefore, all einsteinium on Earth is produced in laboratories, high-power nuclear reactors, or [[nuclear testing]], and exists only within a few years from the time of the synthesis.<ref name="em"/>

The transuranic elements up to [[fermium]], including einsteinium, should have been present in the [[natural nuclear fission reactor]] at [[Oklo]], but any quantities produced then would have long since decayed away.<ref name="emsley">{{cite book|last=Emsley|first=John|title=Nature's Building Blocks: An A-Z Guide to the Elements|edition=New|date=2011|publisher=Oxford University Press|location=New York, NY|isbn=978-0-19-960563-7}}</ref>

==Synthesis and extraction==
[[File:EsProduction.png|thumb|upright=1.4|Early evolution of einsteinium production in the U.S.<ref name="s51">[[#Seaborg|Seaborg]], p. 51</ref>]]
Einsteinium is produced in minute quantities by bombarding lighter actinides with neutrons in dedicated high-flux [[nuclear reactor]]s. The world's major irradiation sources are the 85-megawatt [[High Flux Isotope Reactor]] (HFIR) at [[Oak Ridge National Laboratory]] (ORNL), Tennessee, U.S.,<ref>{{cite web|title = High Flux Isotope Reactor|url = http://neutrons.ornl.gov/facilities/HFIR/|publisher = Oak Ridge National Laboratory|access-date = 2010-09-23|archive-date = 2015-02-28|archive-url = https://web.archive.org/web/20150228152355/http://neutrons.ornl.gov/facilities/HFIR/|url-status = live}}</ref> and the SM-2 loop reactor at the [[Research Institute of Atomic Reactors]] (NIIAR) in [[Dimitrovgrad, Russia]],<ref>{{cite web|script-title = ru:Радионуклидные источники и препараты|url = http://www.niiar.ru/?q=radioisotope_application|publisher = Research Institute of Atomic Reactors|access-date = 2010-09-26|language = ru|archive-date = 2020-07-26|archive-url = https://web.archive.org/web/20200726202716/http://www.niiar.ru/?q=radioisotope_application|url-status = live}}</ref> which are both dedicated to the production of transcurium (''Z''>96) elements. These facilities have similar power and flux levels, and are expected to have comparable production capacities for transcurium elements,<ref name="h1582">[[#Haire|Haire]], p. 1582</ref> though the quantities produced at NIIAR are not widely reported. In a "typical processing campaign" at ORNL, tens of grams of [[curium]] are irradiated to produce decigram quantities of [[californium]], milligrams of berkelium ({{sup|249}}Bk) and einsteinium and picograms of [[fermium]].<ref>[[#Greenwood|Greenwood]], p. 1262</ref><ref>{{cite journal|first1 = C. E.|last1 = Porter|first2 = F. D. Jr. |last2 = Riley|first3 = R. D.|last3 = Vandergrift|first4 = L. K.|last4 = Felker|title = Fermium Purification Using Teva Resin Extraction Chromatography|journal = Sep. Sci. Technol.|volume = 32|issue = 1–4|date = 1997|pages = 83–92|doi = 10.1080/01496399708003188|url = https://zenodo.org/record/1234415|access-date = 2018-05-18|archive-date = 2020-03-11|archive-url = https://web.archive.org/web/20200311030820/https://zenodo.org/record/1234415|url-status = live}}</ref>

The first microscopic sample of {{sup|253}}Es sample weighing about 10 [[nanogram]]s was prepared in 1961 at HFIR. A special magnetic balance was designed to estimate its weight.<ref name="CRC"/><ref>Hoffman, Darleane C.; Ghiorso, Albert and Seaborg, Glenn Theodore (2000) ''The Transuranium People: The Inside Story'', Imperial College Press, pp.&nbsp;190–191, {{ISBN|978-1-86094-087-3}}.</ref> Larger batches were produced later starting from several kilograms of plutonium with the einsteinium yields (mostly {{sup|253}}Es) of 0.48 milligram in 1967–1970, 3.2 milligrams in 1971–1973, followed by steady production of about 3 milligrams per year between 1974 and 1978.<ref name="s36">[[#Seaborg|Seaborg]], pp. 36–37</ref> These quantities however refer to the integral amount in the target right after irradiation. Subsequent separation procedures reduced the amount of isotopically pure einsteinium roughly tenfold.<ref name="h1582"/>

===Laboratory synthesis===
Heavy neutron irradiation of plutonium results in four major isotopes of einsteinium: {{sup|253}}Es (α-emitter; half-life 20.47 days, spontaneous fission half-life 7×10{{sup|5}} years); {{sup|254m}}Es (β-emitter, half-life 39.3 hours), {{sup|254}}Es (α-emitter, half-life 276 days) and {{sup|255}}Es (β-emitter, half-life 39.8 days).<ref>{{cite journal|last1=Jones|first1=M.|last2=Schuman|first2=R.|last3=Butler|first3=J.|last4=Cowper|first4=G.|last5=Eastwood|first5=T.|last6=Jackson|first6=H.|title=Isotopes of Einsteinium and Fermium Produced by Neutron Irradiation of Plutonium|journal=Physical Review|volume=102|issue=1|pages=203–207|date=1956|doi=10.1103/PhysRev.102.203|bibcode = 1956PhRv..102..203J }}</ref>{{NUBASE2016|ref}} An alternative route involves bombardment of uranium-238 with high-intensity nitrogen or oxygen ion beams.<ref>{{cite journal|last1=Guseva|first1=L.|last2=Filippova|first2=K.|last3=Gerlit|first3=Y.|last4=Druin|first4=V.|last5=Myasoedov|first5=B.|last6=Tarantin|first6=N.|title=Experiments on the production of einsteinium and fermium with a cyclotron|journal=Journal of Nuclear Energy|volume=3|pages=341–346|date=1956|doi=10.1016/0891-3919(56)90064-X|issue=4}}</ref>

{{sup|247}}Es (half-life 4.55 min) was produced by irradiating {{sup|241}}Am with carbon or {{sup|238}}U with nitrogen ions.<ref name="Binder">Harry H. Binder: ''Lexikon der chemischen Elemente'', S. Hirzel Verlag, Stuttgart 1999, {{ISBN|3-7776-0736-3}}, pp. 18–23.</ref> The latter reaction was first realized in 1967 in Dubna, Russia, and the involved scientists were awarded the [[Lenin Komsomol Prize]].<ref>[http://n-t.ru/ri/ps/pb099.htm Эйнштейний] {{Webarchive|url=https://web.archive.org/web/20210519093938/http://n-t.ru/ri/ps/pb099.htm |date=2021-05-19 }} (in Russian, a popular article by one of the involved scientists)</ref>

{{sup|248}}Es was produced by irradiating {{sup|249}}Cf with [[deuterium]] ions. It mainly β-decays to {{sup|248}}Cf with a half-life of {{val|25|5}} minutes, but also releases 6.87-MeV α-particles; the ratio of β's to α-particles is about 400.<ref>{{cite journal|last1=Chetham-Strode|first1=A.|last2=Holm|first2=L.|title=New Isotope Einsteinium-248|journal=Physical Review|volume=104|pages=1314|date=1956|doi=10.1103/PhysRev.104.1314|issue=5|bibcode = 1956PhRv..104.1314C |s2cid=102836584 }}</ref>
:<math chem>\ce{^{249}_{98}Cf + ^{2}_{1}H -> ^{248}_{99}Es + 3^{1}_{0}n} \quad \left( \ce{^{248}_{99}Es ->[\epsilon][27 \ce{min}] ^{248}_{98}Cf} \right)</math>

{{sup|249, 250, 251, 252}}Es were obtained by bombarding {{sup|249}}Bk with α-particles. One to four neutrons are released, so four different isotopes are formed in one reaction.<ref>{{cite journal|last1=Harvey|first1=Bernard|last2=Chetham-Strode|first2=Alfred|last3=Ghiorso|first3=Albert|last4=Choppin|first4=Gregory|last5=Thompson|first5=Stanley|title=New Isotopes of Einsteinium|journal=Physical Review|volume=104|pages=1315–1319|date=1956|doi=10.1103/PhysRev.104.1315|issue=5|bibcode=1956PhRv..104.1315H|url=http://www.escholarship.org/uc/item/462945g3|access-date=2019-07-14|archive-date=2020-03-12|archive-url=https://web.archive.org/web/20200312004201/https://escholarship.org/uc/item/462945g3|url-status=live|url-access=subscription}}</ref>
:<chem>^{249}_{97}Bk ->[+\alpha] ^{249,250,251,252}_{99}Es</chem>

{{sup|253}}Es was produced by irradiating a 0.1–0.2 milligram {{sup|252}}Cf target with a [[thermal neutron]] flux of (2–5)×10{{sup|14}} neutrons/(cm{{sup|2}}·s) for 500–900 hours:<ref>{{cite journal|last1=Kulyukhin|first1=S.|title=Production of microgram quantities of einsteinium-253 by the reactor irradiation of californium|journal=Inorganica Chimica Acta|volume=110|pages=25–26|date=1985|doi=10.1016/S0020-1693(00)81347-X|last2=Auerman|first2=L. N.|last3=Novichenko|first3=V. L.|last4=Mikheev|first4=N. B.|last5=Rumer|first5=I. A.|last6=Kamenskaya|first6=A. N.|last7=Goncharov|first7=L. A.|last8=Smirnov|first8=A. I.}}</ref>
:<chem>^{252}_{98}Cf ->[\ce{(n,\gamma)}] ^{253}_{98}Cf ->[\beta^-][17.81 \ce{d}] ^{253}_{99}Es</chem>

In 2020, scientists at ORNL created about 200 nanograms of {{sup|254}}Es; allowing some chemical properties of the element to be studied for the first time.<ref>{{cite journal|title=Structural and spectroscopic characterization of an einsteinium complex|date=3 February 2021|access-date=3 February 2021|url=https://www.nature.com/articles/s41586-020-03179-3|journal=Nature|volume=590|pages=85–88|doi=10.1038/s41586-020-03179-3|first1=Korey P.|last1=Carter|first2=Katherine M.|last2=Shield|first3=Kurt F.|last3=Smith|first4=Zachary R.|last4=Jones|first5=Jennifer N.|last5=Wacker|first6=Leticia|last6=Arnedo-Sanchez|first7=Tracy M.|last7=Mattox|first8=Liane M.|last8=Moreau|first9=Karah E.|last9=Knope|first10=Stosh A.|last10=Kozimor|first11=Corwin H.|last11=Booth|first12=Rebecca J.|last12=Abergel|issue=7844|pmid=33536647|bibcode=2021Natur.590...85C|osti=1777970 |s2cid=231805413|archive-date=3 February 2021|archive-url=https://web.archive.org/web/20210203162013/https://www.nature.com/articles/s41586-020-03179-3|url-status=live}}</ref>

===Synthesis in nuclear explosions===
[[File:ActinideExplosionSynthesis.png|thumb|upright=1.4|left|Estimated yield of transuranium elements in the U.S. nuclear tests Hutch and Cyclamen<ref name="s40"/>]]
The analysis of the debris at the 10-[[TNT equivalent|megaton]] ''Ivy Mike'' nuclear test was a part of long-term project. One of the goals was studying the efficiency of production of transuranic elements in high-power nuclear explosions. The motive for these experiments was that synthesis of such elements from uranium requires multiple neutron capture. The probability of such events increases with the [[neutron flux]], and nuclear explosions are the most powerful man-made neutron sources, providing densities of the order 10{{sup|23}} neutrons/cm{{sup|2}} within a microsecond, or about 10{{sup|29}} neutrons/(cm{{sup|2}}·s). In comparison, the flux of HFIR is 5{{e|15}} neutrons/(cm{{sup|2}}·s). A dedicated laboratory was set up right at [[Enewetak Atoll]] for preliminary analysis of debris, as some isotopes could have decayed by the time the debris samples reached the mainland U.S. The laboratory was receiving samples for analysis as soon as possible, from airplanes equipped with paper filters which flew over the atoll after the tests. Whereas it was hoped to discover new chemical elements heavier than fermium, none of these were found even after a series of megaton explosions conducted between 1954 and 1956 at the atoll.<ref name="s39"/>

The atmospheric results were supplemented by the underground test data accumulated in the 1960s at the [[Nevada Test Site]], as it was hoped that powerful explosions in a confined space might give improved yields and heavier isotopes. Apart from traditional uranium charges, combinations of uranium with americium and [[thorium]] have been tried, as well as a mixed plutonium-neptunium charge, but they were less successful in terms of yield and was attributed to stronger losses of heavy isotopes due to enhanced fission rates in heavy-element charges. Product isolation was problematic as the explosions were spreading debris through melting and vaporizing the surrounding rocks at depths of 300–600 meters. Drilling to such depths to extract the products was both slow and inefficient in terms of collected volumes.<ref name="s39"/><ref name="s40">[[#Seaborg|Seaborg]], p. 40</ref>

Of the nine underground tests between 1962 and 1969,<ref>These were codenamed: "Anacostia" (5.2 [[TNT equivalent|kilotons]], 1962), "Kennebec" (<5 kilotons, 1963), "Par" (38 kilotons, 1964), "Barbel" (<20 kilotons, 1964), "Tweed" (<20 kilotons, 1965), "Cyclamen" (13 kilotons, 1966), "Kankakee" (20-200 kilotons, 1966), "Vulcan" (25 kilotons, 1966) and "Hutch" (20-200 kilotons, 1969)</ref><ref>[http://www.nv.doe.gov/library/publications/historical/DOENV_209_REV15.pdf United States Nuclear Tests July 1945 through September 1992] {{webarchive |url=https://web.archive.org/web/20100615231826/http://www.nv.doe.gov/library/publications/historical/DOENV_209_REV15.pdf |date=June 15, 2010 }}, DOE/NV--209-REV 15, December 2000.</ref> the last one was the most powerful and had the highest yield of transuranics. Milligrams of einsteinium that would normally take a year of irradiation in a high-power reactor, were produced within a microsecond.<ref name="s40"/> However, the major practical problem of the entire proposal was collecting the radioactive debris dispersed by the powerful blast. Aircraft filters adsorbed only ~4{{e|-14}} of the total amount, and collection of tons of corals at Enewetak Atoll increased this fraction by only two orders of magnitude. Extraction of about 500 kilograms of underground rocks 60 days after the Hutch explosion recovered only ~1{{e|-7}} of the total charge. The amount of transuranic elements in this 500 kg batch was only 30 times higher than in a 0.4-kg rock picked up 7 days after the test which showed the highly non-linear dependence of the transuranics yield on the amount of retrieved radioactive rock.<ref name="s43">[[#Seaborg|Seaborg]], p. 43</ref> Shafts were drilled at the site before the test in order to accelerate sample collection after explosion, so that explosion would expel radioactive material from the epicenter through the shafts and to collecting volumes near the surface. This method was tried in two tests and instantly provided hundreds of kilograms of material, but with actinide concentration three times lower than in samples obtained after drilling. Whereas such method could have been efficient in scientific studies of short-lived isotopes, it could not improve the overall collection efficiency of the produced actinides.<ref name="s44">[[#Seaborg|Seaborg]], p. 44</ref>

Though no new elements (except einsteinium and fermium) could be detected in the nuclear test debris, and the total yields of transuranics were disappointingly low, these tests did provide significantly higher amounts of rare heavy isotopes than previously available in laboratories.<!-- About 6E9 atoms of 257Fm could be recovered after the Hutch detonation. These were then used in the studies of thermal-neutron induced fission of 257Fm, and in discovery of a new nuclide, 258Fm. Also, the rare 250Cm isotope was synthesized in large quantities, which is very hard to produce in nuclear reactors from its progenitor 249Cm: 249Cm's half-life (64 minutes) is much too short for months-long reactor irradiation, but very "long" on the timescale of an explosion.--><ref name="s47">[[#Seaborg|Seaborg]], p. 47</ref>

===Separation===
[[File:Elutionskurven Fm Es Cf Bk Cm Am.png|thumb|[[Elution]] curves: chromatographic separation of Fm(100), Es(99), Cf, Bk, Cm and Am]]
Separation procedure of einsteinium depends on the synthesis method. In the case of light-ion bombardment inside a cyclotron, the heavy ion target is attached to a thin foil, and the generated einsteinium is simply washed off the foil after the irradiation. However, the produced amounts in such experiments are relatively low.<ref name="h1583">[[#Haire|Haire]], p. 1583</ref> The yields are much higher for reactor irradiation, but there, the product is a mixture of various actinide isotopes, as well as lanthanides produced in the nuclear fission decays. In this case, isolation of einsteinium is a tedious procedure which involves several repeating steps of cation exchange, at elevated temperature and pressure, and chromatography. Separation from berkelium is important, because the most common einsteinium isotope produced in nuclear reactors, {{sup|253}}Es, decays with a half-life of only 20 days to {{sup|249}}Bk, which is fast on the timescale of most experiments. Such separation relies on the fact that berkelium easily oxidizes to the solid +4 state and precipitates, whereas other actinides, including einsteinium, remain in their +3 state in solutions.<ref name="h1584">[[#Haire|Haire]], pp. 1584–1585</ref>

Trivalent actinides can be separated from lanthanide fission products by a cation-exchange resin column using a 90% water/10% ethanol solution saturated with [[hydrochloric acid]] (HCl) as [[eluant]]. It is usually followed by [[anion-exchange chromatography]] using 6 [[molar concentration|molar]] HCl as eluant. A cation-exchange resin column (Dowex-50 exchange column) treated with ammonium salts is then used to separate fractions containing elements 99, 100 and 101. These elements can be then identified simply based on their elution position/time, using α-hydroxyisobutyrate solution (α-HIB), for example, as eluant.<ref name="book2">{{cite book|url=https://books.google.com/books?id=U4rnzH9QbT4C&pg=PA11|pages=9–11|title=The new chemistry|last=Hall, Nina|publisher=Cambridge University Press|date=2000|isbn=978-0-521-45224-3|access-date=2016-01-05|archive-date=2016-05-20|archive-url=https://web.archive.org/web/20160520024221/https://books.google.com/books?id=U4rnzH9QbT4C&pg=PA11|url-status=live}}</ref>

The 3+ actinides can also be separated via solvent extraction chromatography, using bis-(2-ethylhexyl) phosphoric acid (abbreviated as HDEHP) as the stationary organic phase, and nitric acid as the mobile aqueous phase. The actinide elution sequence is reversed from that of the cation-exchange resin column. The einsteinium separated by this method has the advantage to be free of organic complexing agent, as compared to the separation using a resin column.<ref name="book2"/>

===Preparation of the metal===
Einsteinium is highly reactive, so strong reducing agents are required to obtain the pure metal from its compounds.<ref name="h1588">[[#Haire|Haire]], p. 1588</ref> This can be achieved by reduction of [[einsteinium(III) fluoride]] with metallic [[lithium]]:
:EsF{{sub|3}} + 3 Li → Es + 3 LiF

However, owing to its low melting point and high rate of self-radiation damage, einsteinium has a higher vapor pressure than [[lithium fluoride]]. This makes this reduction reaction rather inefficient. It was tried in the early preparation attempts and quickly abandoned in favor of reduction of einsteinium(III) oxide with [[lanthanum]] metal:<ref name="ev">{{cite journal|last1=Haire|first1=R.|title=Preparation, properties, and some recent studies of the actinide metals|url=http://www.osti.gov/bridge/product.biblio.jsp?osti_id=5235830|doi=10.1016/0022-5088(86)90554-0|date=1986|pages=379–398|volume=121|journal=Journal of the Less Common Metals|osti=5235830 |s2cid=97518446 |access-date=2010-11-24|archive-date=2013-05-13|archive-url=https://web.archive.org/web/20130513130241/http://www.osti.gov/bridge/product.biblio.jsp?osti_id=5235830|url-status=live}}</ref><ref name="ES_METALL"/><ref name="h1590">[[#Haire|Haire]], p. 1590</ref>
:Es{{sub|2}}O{{sub|3}} + 2 La → 2 Es + La{{sub|2}}O{{sub|3}}

==Chemical compounds==
{{Main|Einsteinium compounds}}

{|class = wikitable
|+Crystal structure and lattice constants of some Es compounds
!Compound!!Color !! Symmetry!![[Space group]]!!No!![[Pearson symbol]]||''a'' ([[picometre|pm]])!!''b'' (pm)!!''c'' (pm)
|-
|Es{{sub|2}}O{{sub|3}}|| Colorless||Cubic<ref name="ES2O3"/>||Ia{{overline|3}}|| 206||cI80||1076.6|| ||
|-
|Es{{sub|2}}O{{sub|3}}|| Colorless||[[Monoclinic crystal system|Monoclinic]]<ref name="ox1"/>||C2/m||12|| mS30||1411||359 || 880
|-
|Es{{sub|2}}O{{sub|3}}|| Colorless||Hexagonal<ref name="ox1"/>|| P{{overline|3}}m1||164 ||hP5||370|| ||600
|-
|EsF{{sub|3}}|| ||Hexagonal<ref name="ES_F3"/>|| || || || || ||
|-
|EsF{{sub|4}}|| ||Monoclinic<ref>{{cite journal|last1=Kleinschmidt|first1=P.|title=Thermochemistry of the actinides|journal=Journal of Alloys and Compounds|volume=213–214|pages=169–172|date=1994|doi=10.1016/0925-8388(94)90898-2|url=https://digital.library.unt.edu/ark:/67531/metadc1401691/|access-date=2019-07-14|archive-date=2020-03-16|archive-url=https://web.archive.org/web/20200316233629/https://digital.library.unt.edu/ark:/67531/metadc1401691/|url-status=live}}</ref> || C2/c||15 ||mS60 || || ||
|-
|EsCl{{sub|3}}||Orange||Hexagonal<ref>{{cite journal|last1=Fujita|first1=D.|title=Crystal structures and lattice parameters of einsteinium trichloride and einsteinium oxychloride|journal=Inorganic and Nuclear Chemistry Letters|volume=5|pages=307–313|date=1969|doi=10.1016/0020-1650(69)80203-5|issue=4|last2=Cunningham|first2=B. B.|last3=Parsons|first3=T. C.|url=http://www.escholarship.org/uc/item/7hz778j2|access-date=2019-07-14|archive-date=2020-03-13|archive-url=https://web.archive.org/web/20200313022142/https://escholarship.org/uc/item/7hz778j2|url-status=live}}</ref><ref name="m99"/>|| C6{{sub|3}}/m|| ||hP8 ||727 || ||410
|-
|EsBr{{sub|3}}||Yellow||Monoclinic<ref>{{cite journal|last1=Fellows|first1=R.|title=X-ray diffraction and spectroscopic studies of crystalline einsteinium(III) bromide, {{sup|253}}EsBr{{sub|3}}|journal=Inorganic and Nuclear Chemistry Letters|volume=11|pages=737–742|date=1975|doi=10.1016/0020-1650(75)80090-0|issue=11|last2=Peterson|first2=J. R.|last3=Noé|first3=M.|last4=Young|first4=J. P.|last5=Haire|first5=R. G.}}</ref>||C2/m || 12|| mS16||727 ||1259 || 681
|-
|EsI{{sub|3}}||Amber||Hexagonal<ref name="h1595"/><ref name="s62">[[#Seaborg|Seaborg]], p. 62</ref>||R{{overline|3}} ||148 ||hR24 || 753|| ||2084
|-
|EsOCl|| ||Tetragonal<ref name="h1595">[[#Haire|Haire]], pp. 1595–1596</ref><ref name="YOUNG_1981"/>|| P4/nmm|| || ||394.8 || || 670.2
|}

===Oxides===
Einsteinium(III) oxide (Es{{sub|2}}O{{sub|3}}) was obtained by burning einsteinium(III) nitrate. It forms colorless cubic crystals, which were first characterized from microgram samples sized about 30 nanometers.<ref name="g1268">[[#Greenwood|Greenwood]], p. 1268</ref><ref name="ES2O3">{{cite journal|last1=Haire|first1=R. G.|last2=Baybarz|first2=R. D.|title=Identification and analysis of einsteinium sesquioxide by electron diffraction|journal=Journal of Inorganic and Nuclear Chemistry|volume=35|pages=489–496|date=1973|doi=10.1016/0022-1902(73)80561-5|issue=2}}</ref> Two other phases, [[Monoclinic crystal system|monoclinic]] and hexagonal, are known for this oxide. The formation of a certain Es{{sub|2}}O{{sub|3}} phase depends on the preparation technique and sample history, and there is no clear phase diagram. Interconversions between the three phases can occur spontaneously, as a result of self-irradiation or self-heating.<ref name="h1598">[[#Haire|Haire]], p. 1598</ref> The hexagonal phase is isotypic with [[lanthanum oxide]] where the Es{{sup|3+}} ion is surrounded by a 6-coordinated group of O{{sup|2−}} ions.<ref name="ox1">{{cite book|title=Handbook on the Physics and Chemistry of Rare Earths|volume=18|chapter=Lanthanides and Actinides Chemistry|editor=K.A. Gscheidner, Jr. |display-editors=etal|location=North-Holland, New York|date=1994|pages=414–505|isbn=978-0-444-81724-2|last=Haire, R. G.|last2=Eyring, L.|name-list-style=amp}}</ref><ref name="h1595"/>

===Halides===
[[File:Einsteinium triiodide by transmitted light.jpg|thumb|[[Einsteinium(III) iodide]] glowing in the dark]]

Einsteinium [[halide]]s are known for the oxidation states +2 and +3.<ref name="YOUNG_1981">{{cite journal|last1=Young|first1=J. P.|last2=Haire|first2=R. G.|last3=Peterson|first3=J. R.|last4=Ensor|first4=D. D.|last5=Fellow|first5=R. L.|title=Chemical consequences of radioactive decay. 2. Spectrophotometric study of the ingrowth of berkelium-249 and californium-249 into halides of einsteinium-253|journal=Inorganic Chemistry|volume=20|pages=3979–3983|date=1981|doi=10.1021/ic50225a076|issue=11}}</ref><ref name = "HOWI_1969">[[#Holleman|Holleman]], p. 1969</ref> The most stable state is +3 for all halides from fluoride to iodide.

Einsteinium(III) fluoride (EsF{{sub|3}}) can be precipitated from Es(III) chloride solutions upon reaction with [[fluoride]] ions. An alternative preparation procedure is to exposure Es(III) oxide to [[chlorine trifluoride]] (ClF{{sub|3}}) or F{{sub|2}} gas at a pressure of 1–2 atmospheres and temperature 300–400°C. The EsF{{sub|3}} crystal structure is hexagonal, as in californium(III) fluoride (CfF{{sub|3}}) where the Es{{sup|3+}} ions are 8-fold coordinated by fluorine ions in a bicapped [[Octahedral molecular geometry#Trigonal prismatic geometry|trigonal prism]] arrangement.<ref name="ES_F3">{{cite journal|last1=Ensor|first1=D. D.|last2=Peterson|first2=J. R.|last3=Haire|first3=R. G.|last4=Young|first4=J. P.|title=Absorption spectrophotometric study of {{sup|253}}EsF{{sub|3}} and its decay products in the bulk-phase solid state|journal=Journal of Inorganic and Nuclear Chemistry|volume=43|pages=2425–2427|date=1981|doi=10.1016/0022-1902(81)80274-6|issue=10}}</ref><ref name="g1270">[[#Greenwood|Greenwood]], p. 1270</ref><ref>{{cite journal|last1=Young|first1=J. P.|last2=Haire|first2=R. G.|last3=Fellows|first3=R. L.|last4=Peterson|first4=J. R.|title=Spectrophotometric studies of transcurium element halides and oxyhalides in the solid state|journal=Journal of Radioanalytical Chemistry|volume=43|pages=479–488|date=1978|doi=10.1007/BF02519508|issue=2|bibcode=1978JRNC...43..479Y |s2cid=95361392}}</ref>

Es(III) chloride (EsCl{{sub|3}}) can be prepared by annealing Es(III) oxide in the atmosphere of dry hydrogen chloride vapors at about 500°C for some 20 minutes. It crystallizes upon cooling at about 425°C into an orange solid with a [[hexagonal crystal family|hexagonal]] structure of [[uranium(III) chloride|UCl{{sub|3}} type]], where einsteinium atoms are 9-fold coordinated by chlorine atoms in a tricapped trigonal prism geometry.<ref name="m99">Miasoedov, B. F. Analytical chemistry of transplutonium elements, Wiley, 1974 (Original from the University of California), {{ISBN|0-470-62715-8}}, p. 99</ref><ref name="g1270"/><ref>{{cite journal|last1=Fujita|first1=D.|title=The solution absorption spectrum of Es<sup>3+</sup>|journal=Inorganic and Nuclear Chemistry Letters|volume=5|pages=245–250|date=1969|doi=10.1016/0020-1650(69)80192-3|issue=4|last2=Cunningham|first2=B. B.|last3=Parsons|first3=T. C.|last4=Peterson|first4=J. R.|url=http://www.escholarship.org/uc/item/3s43w87r|access-date=2019-07-14|archive-date=2020-03-09|archive-url=https://web.archive.org/web/20200309022304/https://escholarship.org/uc/item/3s43w87r|url-status=live}}</ref> [[Einsteinium(III) bromide]] (EsBr{{sub|3}}) is a pale-yellow solid with a [[monoclinic crystal system|monoclinic]] structure of [[aluminium chloride|AlCl{{sub|3}} type]], where the einsteinium atoms are [[Octahedral molecular geometry|octahedrally]] coordinated by bromine (coordination number 6).<ref name="s62"/><ref name="g1270"/>

The divalent compounds of einsteinium are obtained by reducing the trivalent halides with [[hydrogen]]:<ref name="ES_II">{{cite journal|url=http://hal.archives-ouvertes.fr/docs/00/21/88/31/PDF/ajp-jphyscol197940C435.pdf|title=Preparation, characterization, and decay of einsteinium(II) in the solid state|journal=Le Journal de Physique|last=Peterson, J.R.|display-authors=etal|volume=40|issue=4|page=C4–111|date=1979|doi=10.1051/jphyscol:1979435|citeseerx=10.1.1.729.8671|s2cid=95575017 |access-date=2010-11-24|archive-date=2012-03-07|archive-url=https://web.archive.org/web/20120307233035/http://hal.archives-ouvertes.fr/docs/00/21/88/31/PDF/ajp-jphyscol197940C435.pdf|url-status=live}} [http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=6593662 manuscript draft] {{Webarchive|url=https://web.archive.org/web/20130513121141/http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=6593662 |date=2013-05-13 }}</ref>
:2 EsX{{sub|3}} + H{{sub|2}} → 2 EsX{{sub|2}} + 2 HX; X = F, Cl, Br, I

[[Einsteinium(II) chloride]] (EsCl{{sub|2}}),<ref>Fellows, R.L.; Young, J.P.; Haire, R.G. and Peterson J.R. (1977) in: GJ McCarthy and JJ Rhyne (eds) ''The Rare Earths in Modern Science and Technology'', Plenum Press, New York, pp. 493–499.</ref> [[einsteinium(II) bromide]] (EsBr{{sub|2}})<ref>Young, J.P.; Haire R.G., Fellows, R.L.; Noe, M. and Peterson, J.R. (1976) "Spectroscopic and X-Ray Diffraction Studies of the Bromides of Californium-249 and Einsteinium-253", in: W. Müller and R. Lindner (eds.) ''Plutonium 1975'', North Holland, Amsterdam, pp. 227–234.</ref> and [[einsteinium(II) iodide]] (EsI{{sub|2}})<ref name = "YOUNG_1981"/> have been produced and characterized by optical absorption, with no structural information available yet.<ref name="s62"/>

Known oxyhalides of einsteinium include EsOCl,<ref name="YOUNG_1981"/> EsOBr<ref name="ES_II"/> and EsOI.<ref name="YOUNG_1981"/> These salts are synthesized by treating a trihalide with a vapor mixture of water and the corresponding hydrogen halide: for example, EsCl{{sub|3}} + H{{sub|2}}O/HCl to obtain EsOCl.<ref name="s60">[[#Seaborg|Seaborg]], p. 60</ref>

===Organoeinsteinium compounds===
Einsteinium's high radioactivity has a potential use in [[radiation therapy]], and organometallic complexes have been synthesized in order to deliver einsteinium to an appropriate organ in the body. Experiments have been performed on injecting einsteinium [[citric acid|citrate]] (as well as fermium compounds) to dogs.<ref name="h1579"/> Einsteinium(III) was also incorporated into β-diketone [[Chelation|chelate]] complexes, since analogous complexes with lanthanides previously showed strongest UV-excited [[luminescence]] among metallorganic compounds. When preparing einsteinium complexes, the Es{{sup|3+}} ions were 1000 times diluted with Gd{{sup|3+}} ions. This allowed reducing the radiation damage so that the compounds did not disintegrate during the 20 minutes required for the measurements. The resulting luminescence from Es{{sup|3+}} was much too weak to be detected. This was explained by the unfavorable relative energies of the individual constituents of the compound that hindered efficient energy transfer from the chelate matrix to Es{{sup|3+}} ions. Similar conclusion was drawn for americium, berkelium and fermium.<ref>{{cite journal|last1=Nugent|first1=Leonard J.|last2=Burnett|first2=J. L.|last3=Baybarz|first3=R. D.|last4=Werner|first4=George Knoll|last5=Tanner|first5=S. P.|last6=Tarrant|first6=J. R.|last7=Keller|first7=O. L.|title=Intramolecular energy transfer and sensitized luminescence in actinide(III) .beta.-diketone chelates|journal=The Journal of Physical Chemistry|volume=73|pages=1540–1549|date=1969|doi=10.1021/j100725a060|issue=5 |bibcode=1969JPhCh..73.1540N }}</ref>

Luminescence of Es{{sup|3+}} ions was however observed in inorganic hydrochloric acid solutions as well as in organic solution with di(2-ethylhexyl)orthophosphoric acid. It shows a broad peak at about 1064 nanometers (half-width about 100&nbsp;nm) which can be resonantly excited by green light (ca. 495&nbsp;nm wavelength). The luminescence has a lifetime of several microseconds and the quantum yield below 0.1%. The relatively high, compared to lanthanides, non-radiative decay rates in Es{{sup|3+}} were associated with the stronger interaction of f-electrons with the inner Es{{sup|3+}} electrons.<ref>{{cite journal|last1=Beitz|first1=J.|last2=Wester|first2=D.|last3=Williams|first3=C.|title=5f state interaction with inner coordination sphere ligands: Es{{sup|3+}} ion fluorescence in aqueous and organic phases|journal=Journal of the Less Common Metals|volume=93|pages=331–338|date=1983|doi=10.1016/0022-5088(83)90178-9|issue=2}}</ref>

==Applications==
There is almost no use for any isotope of einsteinium outside basic scientific research aiming at production of higher [[transuranium element]]s and [[superheavy element]]s.<ref>[http://education.jlab.org/itselemental/ele099.html It's Elemental – The Element Einsteinium] {{Webarchive|url=https://web.archive.org/web/20190710170841/http://education.jlab.org/itselemental/ele099.html |date=2019-07-10 }}. Retrieved 2 December 2007.</ref>

In 1955, [[mendelevium]] was synthesized by irradiating a target consisting of about 10{{sup|9}} atoms of {{sup|253}}Es in the 60-inch cyclotron at Berkeley Laboratory. The resulting {{sup|253}}Es(α,n){{sup|256}}Md reaction yielded 17 atoms of the new element with the atomic number of 101.<ref name="discovery">{{cite journal|doi=10.1103/PhysRev.98.1518|url=https://books.google.com/books?id=e53sNAOXrdMC&pg=PA101|isbn=978-981-02-1440-1|title=New Element Mendelevium, Atomic Number 101|date=1955|last1=Ghiorso|first1=A.|last2=Harvey|first2=B.|last3=Choppin|first3=G.|last4=Thompson|first4=S.|last5=Seaborg|first5=G.|journal=Physical Review|volume=98|pages=1518–1519|issue=5|bibcode=1955PhRv...98.1518G|access-date=2016-01-05|archive-date=2016-05-18|archive-url=https://web.archive.org/web/20160518212418/https://books.google.com/books?id=e53sNAOXrdMC&pg=PA101|url-status=live|doi-access=free}}</ref>

The rare isotope [[isotopes of einsteinium|{{sup|254}}Es]] is favored for production of [[superheavy element]]s due to its large mass, relatively long half-life of 270 days, and availability in significant amounts of several micrograms.<ref>{{cite journal|last1=Schadel|first1=M.|last2=Bruchle|first2=W.|last3=Brugger|first3=M.|last4=Gaggeler|first4=H.|last5=Moody|first5=K.|last6=Schardt|first6=D.|last7=Summerer|first7=K.|last8=Hulet|first8=E.|last9=Dougan|first9=A.|first10=R.|last10=Dougan|first11=J.|last11=Landrum|first12=R.|last12=Lougheed|first13=J.|last13=Wild|first14=G.|last14=O'Kelley|first15=R.|last15=Hahn|title=Heavy isotope production by multinucleon transfer reactions with {{sup|254}}Es|journal=Journal of the Less Common Metals|volume=122|pages=411–417|date=1986|doi=10.1016/0022-5088(86)90435-2|url=https://zenodo.org/record/1253958|access-date=2018-10-29|archive-date=2020-11-25|archive-url=https://web.archive.org/web/20201125002148/https://zenodo.org/record/1253958|url-status=live}}</ref> Hence {{sup|254}}Es was used as a target in the attempted synthesis of [[ununennium]] (element 119) in 1985 by bombarding it with [[calcium-48]] ions at the superHILAC [[linear particle accelerator]] at Berkeley, California. No atoms were identified, setting an upper limit for the cross section of this reaction at 300 [[barn (unit)|nanobarns]].<ref>{{cite journal|title=Search for superheavy elements using {{sup|48}}Ca + {{sup|254}}Es{{sup|g}} reaction|last=Lougheed, R. W.|last2=Landrum, J. H.|last3=Hulet, E. K.|last4=Wild, J. F.|author5=Dougan, R. J.|author6=Dougan, A. D.|author7=Gäggeler, H.|author8=Schädel, M.|author9=Moody, K. J.|author10=Gregorich, K. E.|author11=Seaborg, G. T.|name-list-style=amp|journal=Physical Review C|date=1985|pages=1760–1763|doi=10.1103/PhysRevC.32.1760|pmid=9953034|volume=32|issue=5|bibcode = 1985PhRvC..32.1760L }}</ref>
:<chem>{}^{254}_{99}Es + {}^{48}_{20}Ca -> {}^{302}_{119}Uue^\ast -> no\ atoms</chem>
{{sup|254}}Es was used as the calibration marker in the chemical analysis spectrometer ("[[Surveyor 5#Alpha-scattering surface analyzer|alpha-scattering surface analyzer]]") of the [[Surveyor 5]] lunar probe. The large mass of this isotope reduced the spectral overlap between signals from the marker and the studied lighter elements of the lunar surface.<ref>{{cite journal|doi=10.1126/science.158.3801.635|title=Chemical Analysis of the Moon at the Surveyor V Landing Site|date=1967|last1=Turkevich|first1=A. L.|last2=Franzgrote|first2=E. J.|last3=Patterson|first3=J. H.|journal=Science|volume=158|issue=3801|pages=635–637|pmid=17732956|bibcode = 1967Sci...158..635T |s2cid=21286144}}</ref>

==Safety==
Most of the available einsteinium toxicity data is from research on animals. Upon ingestion by [[Laboratory rat|rats]], only ~0.01% of it ends in the bloodstream. From there, about 65% goes to the bones, where it would remain for ~50 years if not for its radioactive decay, not to speak of the three-year maximum lifespan of rats, 25% to the lungs (biological half-life ~20 years, though this is again rendered irrelevant by the short half-life of einsteinium), 0.035% to the testicles or 0.01% to the ovaries—where einsteinium stays indefinitely. About 10% of the ingested amount is excreted. The distribution of einsteinium over bone surfaces is uniform and is similar to that of plutonium.<ref>{{cite book|last=International Commission on Radiological Protection|title=Limits for intakes of radionuclides by workers, Part 4|issue=4|volume=19|url=https://books.google.com/books?id=WTxcCV4w0VEC&pg=PA18|isbn=978-0-08-036886-3|publisher=Elsevier Health Sciences|date=1988|pages=18–19|access-date=2016-01-05|archive-date=2016-04-25|archive-url=https://web.archive.org/web/20160425000452/https://books.google.com/books?id=WTxcCV4w0VEC&pg=PA18|url-status=live}}</ref>

==References==
{{Reflist|30em}}

==Bibliography==
* {{cite book|ref=Greenwood|last=Greenwood, Norman N.|last2=Earnshaw, Alan |date=1997|title=Chemistry of the Elements |edition=2nd |publisher=Butterworth–Heinemann|isbn=978-0080379418}}
* {{cite book|first = Richard G.|last = Haire|ref = Haire|contribution = Einsteinium|title = The Chemistry of the Actinide and Transactinide Elements|editor1-first = Lester R.|editor1-last = Morss|editor2-first = Norman M.|editor2-last = Edelstein|editor3-first = Jean|editor3-last = Fuger|edition = 3rd|date = 2006|volume = 3|publisher = Springer|location = Dordrecht, the Netherlands|pages = 1577–1620|url = http://radchem.nevada.edu/classes/rdch710/files/einsteinium.pdf|doi = 10.1007/1-4020-3598-5_12|url-status = dead|archive-url = https://web.archive.org/web/20100717154427/http://radchem.nevada.edu/classes/rdch710/files/einsteinium.pdf|archive-date = 2010-07-17|isbn = 978-1-4020-3555-5}}
* {{cite book|ref=Holleman|last=Holleman, Arnold F.|last2=Wiberg, Nils|name-list-style=amp |title=Textbook of Inorganic Chemistry|edition=102nd |publisher=de Gruyter|place= Berlin |date=2007|isbn=978-3-11-017770-1}}
*{{cite book|ref=Seaborg|editor= Seaborg, G.T. |url=http://www.escholarship.org/uc/item/92g2p7cd.pdf |title=Proceedings of the Symposium Commemorating the 25th Anniversary of Elements 99 and 100|date=23 January 1978|publisher=Report LBL-7701}}

==External links==
{{Commons}}
{{wiktionary|einsteinium}}
* [http://www.periodicvideos.com/videos/099.htm Einsteinium] at ''[[The Periodic Table of Videos]]'' (University of Nottingham)
* [https://books.google.com/books?id=cgqNoNWLGBMC&pg=PA311 Age-related factors in radionuclide metabolism and dosimetry: Proceedings] – contains several health related studies of einsteinium
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