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Albert Einstein (īn´stīn), 1879–1955, American theoretical physicist, known for the formulation of the relativity theory, b. Ulm, Germany. He is recognized as one of the greatest physicists of all time.


Einstein lived as a boy in Munich and Milan, continued his studies at the cantonal school at Aarau, Switzerland, and was graduated (1900) from the Federal Institute of Technology, Zürich. Later he became a Swiss citizen. He was examiner (1902–9) at the patent office, Bern. During this period he obtained his doctorate (1905) at the Univ. of Zürich, evolved the special theory of relativity, explained the photoelectric effect, and studied the motion of atoms, on which he based his explanation of Brownian movement. In 1909 his work had already attracted attention among scientists, and he was offered an adjunct professorship at the Univ. of Zürich. He resigned that position in 1910 to become full professor at the German Univ., Prague, and in 1912 he accepted the chair of theoretical physics at the Federal Institute of Technology, Zürich.

By 1913 Einstein had won international fame and was invited by the Prussian Academy of Sciences to come to Berlin as titular professor of physics and as director of theoretical physics at the Kaiser Wilhelm Institute. He assumed these posts in 1914 and subsequently resumed his German citizenship. For his work in theoretical physics, notably on the photoelectric effect, he received the 1921 Nobel Prize in Physics. His property was confiscated (1934) by the Nazi government because he was Jewish, and he was deprived of his German citizenship. He had previously accepted (1933) a post at the Institute for Advanced Study, Princeton, which he held until his death in 1955. An ardent pacifist, Einstein was long active in the cause of world peace; however, in 1939, at the request of a group of scientists, he wrote to President Franklin Delano Roosevelt to stress the urgency of investigating the possible use of atomic energy in bombs. In 1940 he became an American citizen.

Major Contributions to Science

The Special and General Theories of Relativity

Einstein's early work on the theory of relativity (1905) dealt only with systems or observers in uniform (unaccelerated) motion with respect to one another and is referred to as the special theory of relativity; among other results, it demonstrated that two observers moving at great speed with respect to each other will disagree about measurements of length and time intervals made in each other's systems, that the speed of light is the limiting speed of all bodies having mass, and that mass and energy are equivalent. In 1911 he asserted the equivalence of gravitation and inertia, and in 1916 he completed his mathematical formulation of a general theory of relativity that included gravitation as a determiner of the curvature of a space-time continuum. He then began work on his unified field theory, which attempts to explain gravitation, electromagnetism, and subatomic phenomena in one set of laws; the successful development of such a unified theory, however, eluded Einstein.

Photons and the Quantum Theory

In addition to the theory of relativity, Einstein is also known for his contributions to the development of the quantum theory. He postulated (1905) light quanta (photons), upon which he based his explanation of the photoelectric effect, and he developed the quantum theory of specific heat. Although he was one of the leading figures in the development of quantum theory, Einstein regarded it as only a temporarily useful structure. He reserved his main efforts for his unified field theory, feeling that when it was completed the quantization of energy and charge would be found to be a consequence of it. Einstein wished his theories to have that simplicity and beauty which he thought fitting for an interpretation of the universe and which he did not find in quantum theory.


Einstein's writings include Relativity: The Special and the General Theory (1918; tr. 1920, reissued 1947) and excerpts (most of them translated) from letters, articles, and addresses collected in About Zionism (1930), The World as I See It (1934), Out of My Later Years (1950), Ideas and Opinions (1954), and Einstein on Peace (ed. by Otto Nathan and Heinz Norden, 1960). Einstein's manuscripts and correspondence are presently at the Institute for Advanced Study, Princeton. The first volume of an edition of his collected works, under the editorship of John Stachel et al., appeared in 1987.


See the Born-Einstein letters, ed. by M. Born (tr. 1971); biographies by R. W. Clark (1971, repr. 1991), B. Hoffmann (with H. Dukas, 1972, repr. 1989), J. Bernstein (1973, repr. 1997), A. Pais (1982), M. White and J. Gribbin (1995), D. Brian (1997), A. Folsing (1998), W. Isaacson (2007), and J. Neffe (2007); studies by P. A. Schilpp, ed. (1949, repr. 1973), M. Born (rev. ed. 1962), C. Lanczos (1965), A. J. Friedman and C. Donley (1989), D. Howard and J. Stachel (1989), A. Pais (1994), D. Overbye (2000), and Z. Rosenkranz (2011).

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melting point: 1,133K
boiling point: 1,269K
density: 8.8 +/ g/cc
most common ions: Es3+, Es2+

Einsteinium, the tenth member of the actinide series, was discovered in 1952. Einsteinium and fermium (element 100) were most unexpectedly produced in the explosion of the first U.S. thermonuclear device, "Mike," tested at Eniwetok Atoll in the Pacific Ocean on November 1, 1952. Early analyses of debris from that explosion indicated that something unusual had occurred; the new, very neutron-rich isotope of plutonium, 244Pu, was found during mass spectrometric analyses performed at the Argonne National Laboratory and another isotope of plutonium, 246Pu, was detected at the Los Alamos Scientific Laboratory in the course of analyses of the Pu fractions. Scientists at the Radiation Laboratory at the University of California, Berkeley, using their previous experience with the separation of individual actinide elements, then joined in the search for trans-californium elements (elements of higher atomic number than californium). Tons of coral from the atoll were laboriously processed, and 25399 (half-life 20 days) and 255100 (half-life 20 hours) were positively identified based on the order of their elution (removal) from a cation-exchange resin column with an α -hydroxyisobutyrate solution. Because of the huge, nearly instantaneous neutron flux generated in the explosion, at least seventeen neutrons were successively captured by the 238U in the thermonuclear device, producing uranium isotopes through 255U, many of which β -decayed to higher atomic number elements, thus producing 253Es and 255Fm. After their declassification, these results were published jointly by the Berkeley Radiation Laboratory, the Argonne National Laboratory, and the Los Alamos Scientific Laboratory (Ghiorso et al., p. 1048[L], 1955).

The name einsteinium was chosen for element 99, in honor of the great scientist Albert Einstein. Einsteinium isotopes of masses 241 through 256 are known. All are radioactive, decaying by α -particle emission, electron capture, spontaneous fission , and β -decay. The mass 241 isotope has the shortest half-life (8 seconds), and the mass 252 isotope has the longest (1.29 years). The ground state electronic configuration of the gaseous einsteinium atom is [Rn]5f117s2, analogous to that of its lanthanide homologue (holmium). The most stable ion in aqueous solution is Es3+, but Es2+ and Es4+ have been reported, and the metal is divalent.

see also Actinium; Berkelium; Einstein, Albert; Fermium; Lawrencium; Mendelevium; Neptunium; Nobelium; Plutonium; Protactinium; Radioactivity; Rutherfordium; Thorium; Transmutation; Uranium.

Darleane C. Hoffman


Ghiorso, Albert; Thompson, S. G.; Higgins, G. H.; et al. (1955). "New Elements Einsteinium and Fermium, Atomic Numbers 99 and 100." Physical Review 99:1048[L].

Hoffman, Darleane C.; Ghiorso, Albert; and Seaborg, Glenn T. (2000). The Transuranium People: The Inside Story. Singapore: World Scientific Publishing.

Seaborg, Glenn T., and Loveland, Walter D. (1990). The Elements beyond Uranium. New York: Wiley.

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Note: This article, originally published in 1998, was updated in 2006 for the eBook edition.


Einsteinium is a member of the actinide family. The actinide elements are found in Row 7 of the periodic table, a chart that shows how chemical elements are related to each other. The actinides fall between radium (element number 88) and rutherfordium (element number 104). They are usually listed in a separate row at the very bottom of the periodic table.

Einsteinium is also a transuranium element. Transuranium elements are those beyond uranium on the periodic table. Uranium has an atomic number of 92, so elements with larger atomic numbers are transuranium elements.




Transuranium element


Discovery and naming

Einsteinium was discovered by a research team from the University of California at Berkeley. The team was led by Albert Ghiorso (1915- ). The element was discovered in the "ashes" after the first hydrogen bomb test in November 1952 at Eniwetok Atoll, Marshall Islands, in the Pacific Ocean. The discovery was a remarkable accomplishment because no more than a hundred millionth of a gram of the element was present. It was detected because of the characteristic radiation it produced.

Element number 99 was named after German-American physicist Albert Einstein (1879-1955). Some people regard Einstein as the greatest scientist who ever lived.

Physical and chemical properties

Too little einsteinium has been prepared to allow scientists to determine its physical and chemical properties.

Occurrence in nature

Einsteinium does not occur naturally in the Earth's crust.


All isotopes of einsteinium are radioactive. The most stable is einsteinium-252. Its half life is 20.47 days. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope. A radioactive isotope is one that breaks apart and gives off some form of radiation.

The half life of a radioactive element is the time it takes for half of a sample of the element to break down. For example, suppose that scientists made 10 grams of einsteinium. About three weeks later (20.47 days later), only 5 grams of the element would be left. After another three weeks (20.47 days more), only half of that amount (2.5 grams) would remain.


Einsteinium is not extracted from the Earth's crust.


Einsteinium is sometimes used for research purposes, but it has no practical applications.


There are no commercially important compounds of einsteinium.

Einsteinium was named after the great German-American physicist, Albert Einstein.

Health effects

Scientists know too little about einsteinium to be aware of its health effects. As a radioactive element, however, it does pose a threat to human health.

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einsteinium (īn´stī´nēəm, īnstī´–) [for Albert Einstein], artificially produced radioactive chemical element; symbol Es; at. no. 99; mass no. of most stable isotope 252; m.p. about 860°C; b.p. and sp. gr. unknown; valence +2, +3. Einsteinium is a member of Group 3 of the periodic table; its chemical properties are believed to be similar to those of the other members of the actinide series. The seventh transuranium element to be discovered, einsteinium was isolated in Dec., 1952, by Albert Ghiorso and his coworkers at the Univ. of California at Berkeley in residue from the first thermonuclear test explosion in the South Pacific. They identified einsteinium-253, which has a half-life of 20.5 days. It was not until 1961 that a weighable quantity (about 0.01 microgram) of the element was separated; it was used to prepare the element mendelevium. Weighable quantities of einsteinium have since been prepared by neutron bombardment of plutonium. Seventeen isotopes, all of which are radioactive, are known. Einsteinium-252, the most stable isotope, has a half-life of 472 days.

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einsteinium (symbol Es) Radioactive, synthetic metallic element of the actinide series. The isotope, Es253, was first identified in 1952 by US nuclear scientist Albert Ghiorso (1915– ) and colleagues at the University of California at Berkeley; this was after it was found as a decay product of U238 produced by the first large hydrogen bomb explosion. Eleven isotopes have been identified. Properties: at.no. 99; most stable isotope Es254 (half-life 276 days). See also transuranic elements