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Morris Travers, Albert Ghiorso, Marguerite Perey, symbol Xe, electropositive element
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Albumin, one of a class of simple proteins, composed of carbon, hydrogen, oxygen, nitrogen, and a small percentage of sulfur. Albumin is coagulable by heat, mineral acids, alcohol, and ether and is soluble in water and in a weak salt solution. An important part of the diet, albumin is present in such animal tissues as egg white, milk, and muscle and is found in blood plasma; it occurs also in plants, especially in seeds. Because albumin coagulates when heated to 71° C (160° F), it is useful for removing cloudy precipitates, thus clarifying solutions in sugar refining and other processes. Albumin forms insoluble compounds with many metallic salts, such as bichloride of mercury, sulfate of copper, and nitrate of silver, and is, therefore, used as an antidote to these poisons. A paste made of albumin mixed with slaked lime sets to a mass of stony hardness and is used as cement for broken earthenware.
Americium, symbol Am, artificially created, malleable, radioactive metallic element somewhat similar to lead. The atomic number of americium is 95 and its atomic weight is 243. The element is one of the transuranium elements in the actinide series of the periodic table.
Americium was the fourth transuranic element to be synthesized. It was discovered in 1944 and 1945 by the American physicist Glenn Seaborg and his associates at the University of Chicago. They synthesized the americium isotope of mass number 241 by bombarding plutonium-239 with neutrons. Americium isotopes with mass numbers 237 to 247 have been formed; they are all radioactive, with half-lives of from 0.9 minute (americium-232) to about 7,400 years (americium-243). Americium-243 is used as target material in nuclear reactors or particle accelerators for the production of even heavier synthetic elements. Americium melts at 1180°C (2156°F), boils at 2010°C (3650°F), and has a specific gravity of 13.7.
Berkelium, symbol Bk, artificially created radioactive metallic element. The atomic number of berkelium is 97; the element is one of the transuranium elements in the actinide series of the periodic table. Berkelium was discovered in 1949 by the American chemists Glenn T. Seaborg, Stanley G. Thompson, and Albert Ghiorso at the University of California laboratories in Berkeley, California, for which the element was named. An isotope of mass number 243 with a half-life of 4.6 hours was produced by bombarding americium-241 with alpha particles accelerated in a cyclotron. Several other isotopes have subsequently been produced. The most stable isotope of berkelium, with a half-life of about 1,400 years, has a mass number of 247.
Einsteinium, symbol Es, artificially created radioactive element with an atomic number of 99. Einsteinium is one of the transuranium elements in the actinide series of the periodic table. The element was named in honor of German-born American physicist Albert Einstein.
Einsteinium was discovered in 1952 by American chemist Albert Ghiorso and colleagues at the University of California, Berkeley. The scientists discovered the element in the debris produced by a thermonuclear explosion. The isotope first identified had an atomic mass of 253 and a half-life of 20 days. Subsequently, the most long-lived of all the known einsteinium isotopes, einsteinium-254, was prepared by irradiating plutonium in a nuclear reactor; however, only small amounts are now being produced. Isotopes of einsteinium with mass numbers ranging from 241 to 257 are known.
Erbium, symbol Er, metallic element, whose atomic number is 68. The Swedish chemist Carl Gustav Mosander discovered erbium in 1843. Erbium occurs mostly in the same minerals and in the same areas as dysprosium. The elements erbium, terbium, yttrium, and ytterbium were all named for the town of Ytterby in Sweden, the location of a quarry that yielded several rare earth elements.
One of the rare earth elements, erbium is about 43rd in abundance among the elements of Earth's crust. The atomic weight of erbium is 167.26. The element melts at about 1529°C (about 2784°F), boils at about 2868°C (about 5194°F), and has a specific gravity of 9.1.
Metallic erbium has a bright silvery luster. Erbium oxide, Er2O3, is a rose-red compound slowly soluble in many mineral acids, forming a series of rose-colored salts, solutions of which have a sweet, astringent taste. Erbium is used in experimental optical amplifiers that amplify light signals sent along fiber-optic cables.
Europium, symbol Eu, soft, silvery metallic element that is among the least abundant of the rare earth elements. Europium is in the lanthanide series of the periodic table; its atomic number is 63.
Europium was first detected spectroscopically, and was imperfectly isolated by the French chemist Eugene Demarcay in 1901. It ranks 50th in order of abundance of the elements in Earth's crust. The element occurs in monazite, bastnasite, and other rare earth minerals, as well as in fission products of uranium, thorium, and plutonium. Europium melts at 822°C (1512°F) boils at about 1596°C (about 2905°F), and has a specific gravity of 5.2. The atomic weight of europium is 151.96.
Europium is used as a phosphor activator. The screens of some color-television tubes are treated with europium, which, when bombarded with electrons, produces the color red. Because it readily absorbs neutrons, europium is used in the control of nuclear fission in reactors.
Fermium, symbol Fm, artificially created radioactive element with an atomic number of 100. Fermium is one of the transuranium elements in the actinide series of the periodic table. The element was isolated in 1952 from the debris of a hydrogen bomb explosion by the American chemist Albert Ghiorso and coworkers. Subsequently fermium was prepared synthetically in a nuclear reactor by bombarding plutonium with neutrons and in a cyclotron by bombarding uranium-238 with nitrogen ions. Isotopes with mass numbers from 242 to 260 have been produced; fermium-257, the longest-lived of these isotopes, has a half-life of about 100 days. The element was named fermium in 1955 in honor of the Italian-American nuclear physicist Enrico Fermi. Fermium does not have any industrial applications.
Francium, symbol Fr, radioactive metallic element that closely resembles cesium in chemical properties. In group 1 (or Ia) of the periodic table, francium is one of the alkali metals. The atomic number of francium is 87. Marguerite Perey of the Curie Laboratory of the Radium Institute of Paris discovered the element in 1939. The element was named after the country of France.
Francium is produced when the radioactive element actinium disintegrates. Francium is naturally radioactive; its longest-lived isotope, francium-223 (also known as actinium-K) has a half-life of 22 minutes. It emits an extremely energetic beta particle of 1,100,000 electron volts (eV) energy when it decays. Isotopes ranging in atomic weights from 199 to 232 are known.
Francium is the heaviest of the alkali metals; it is the most electropositive element. All its isotopes are radioactive and short-lived. The element is extremely rare, though atoms of francium have been detected in uranium ores.
Indium, symbol In, soft, malleable, silvery white metallic element. The atomic number of indium is 49; the element is in group 13 (or IIIa) of the periodic table.
Indium was discovered spectroscopically in 1863 by the German chemists Hieronymus Theodor Richter and Ferdinand Reich. The element was named for the prominent indigo line in its spectrum. It ranks 63rd in order of abundance of the elements in Earth’s crust. Indium melts at about 157°C (about 315°F), boils at about 2072°C (about 3762°F), and has a specific gravity of 7.3. The atomic weight of indium is 114.82.
Indium never occurs as a free metal and is usually found in certain zinc, tungsten, tin, and iron ores. It is used as an alloying agent with nonferrous metals, in bearing alloys, and in nuclear-reactor control rods. Certain indium compounds have unique semiconductor properties.
Lawrencium, symbol Lr, artificially created radioactive metallic element with an atomic number of 103. Lawrencium is one of the transuranium elements of the periodic table. Named in honor of the American physicist Ernest Lawrence, it was discovered in 1961 at the Lawrence Berkeley National Laboratory of the University of California by American chemist Albert Ghiorso and his colleagues. A mixture of californium isotopes was bombarded with boron ions to produce short-lived lawrencium isotopes. Ten isotopes are now known. The most stable, with a half-life of about 3 minutes, has a mass number of 260. Only small amounts of lawrencium have been produced.
Lutetium, symbol Lu, silvery white metallic element with an atomic number of 71. Lutetium is one of the transition elements of the periodic table.
Lutetium was discovered independently by two investigators, the French chemist Georges Urbain in 1907 and the Austrian chemist Carl Auer von Welsbach about the same time. It was named by Urbain, who derived the word from Lutetia, the ancient name of Paris. Lutetium occurs in various rare earth minerals, usually associated with yttrium. It is the rarest of the rare earth elements and ranks 59th in order of abundance of the elements in Earth's crust. Several trivalent salts are known. A natural radioactive isotope of lutetium that has a half-life of about 30 billion years is used in determining the age of meteorites.
Lutetium melts at about 1663°C (about 3025°F), boils at about 3402°C (about 6156°F) and has a specific gravity of 9.84. The atomic weight of lutetium is 174.97.
Mendelevium, symbol Md, artificially created radioactive element with an atomic number of 101. Mendelevium is one of the transuranium elements in the actinide series of the periodic table. Named for the Russian chemist Dmitry Mendeleyev, mendelevium-256 was discovered in 1955 at the University of California, Berkeley; it was produced by bombarding einsteinium-253 with alpha particles accelerated in a cyclotron. The isotope produced had a half-life of about 1.3 hours. The most stable isotope, mendelevium-258, has a half-life of just over 51 days.
Neodymium (Greek neos + didymos, “new twin”), symbol Nd, silvery metallic element with an atomic number of 60. Neodymium is one of the rare earth elements in the lanthanide series of the periodic table. Neodymium was isolated in 1885 by the Austrian chemist Baron Carl Auer von Welsbach, who separated it from praseodymium. Neodymium and praseodymium had previously been regarded as a single element, called didymium.
Neodymium occurs in the minerals bastnasite and monazite, as do many of the rare earth elements. Neodymium ranks about 27th in order of abundance of the elements in Earth's crust. It forms trivalent salts, which are rose-red or reddish-violet in color. The metal's oxide, Nd2O3, is used in the glass of color-television tubes to increase contrast, and in lasers.
Neodymium melts at about 1021°C (about 1870°F), boils at about 3074°C (about 5565°F), and has a specific gravity of 7.01. The atomic weight of neodymium is 144.24.
Nobelium, symbol No, radioactive metallic element with an atomic number of 102. Nobelium is one of the transuranium elements in the actinide series of the periodic table. The element is named for the Swedish inventor and philanthropist Alfred Bernhard Nobel.
Nobelium is not found in nature but is produced artificially in the laboratory. Separate discovery of the element was first claimed in 1957 by scientific groups in the United States, Britain, and Sweden, but the first confirmed discovery of a nobelium isotope, by a team of scientists at the Lawrence Berkeley National Laboratory in Berkeley, California, took place in 1958. The isotope was created by bombarding curium isotopes with carbon ions.
Chemically, the properties of nobelium are unknown, but because it is an actinide, its properties should somewhat resemble those of the rare earth elements. Several isotopes are now known. The most stable isotope, nobelium-259, has a half-life of 58 minutes.
Petrolatum, odorless, tasteless, greasy substance, obtained as the residue from petroleum after the lighter and more volatile components have been boiled off. The purified residue is obtained in the form of a yellowish or decolorized semisolid, known as petroleum jelly, or by various trademark names, such as Vaseline, and in the form of a clear to faintly yellow liquid, known as mineral oil. The semisolid form is used as an unguent and as a base for pharmaceutical ointments; the liquid form is used as a laxative.
Protactinium, formerly protoactinium, symbol Pa, radioactive metallic element with an atomic number of 91. Protactinium is a member of the actinide series of the periodic table. It was discovered in 1913 by Kasimir Fajans and Otto H. Gohring.
Protactinium is a member of the uranium-actinium radioactive-decay series and trace amounts are found in uranium ores such as pitchblende. Isotopes of protactinium ranging in mass number from 212 to 239 are known; the element’s atomic weight is 231.04. Protactinium-233 has a half-life of 27 days. Protactinium-231, the most stable isotope, has a half-life of more than 32,500 years; it decays to actinium by emission of an alpha particle. This decay chain gave protactinium its name, which is a shortened form of proto-actinium. Protactinium melts at about 1572°C (about 2862°F), boils at about 4227°C (about 7641°F), and has a specific gravity of about 15.37.
Samarium, symbol Sm, hard, brittle, lustrous metallic element. Samarium is one of the rare earth elements in the lanthanide series of the periodic table. The atomic number of samarium is 62.
Samarium was discovered in 1879 by the French chemist P. E. Lecoq de Boisbaudran in the mineral samarskite. The element is named for the mineral. The metal ignites in air at about 150°C (about 302°F). Like other rare earth metals, it is found in minerals such as monazite, bastnasite, cerite, gadolinite, and samarskite. Samarium is about 40th in order of abundance of the elements in Earth's crust. The element forms chiefly trivalent compounds; the salts are pale yellow in color. Samarium oxide is used in the control rods of some nuclear reactors.
Samarium melts at about 1074°C (about 1965°F), boils at about 1794°C (about 3261°F), and has a specific gravity of 7.52. The atomic weight of samarium is 150.4.
Scandium, symbol Sc, soft, silver-white metallic element with an atomic number of 21. Scandium is one of the transition elements in the periodic table.
Scandium was discovered in 1879 by the Swedish chemist Lars Fredrik Nilson, eight years after the Russian chemist Dmitry Ivanovich Mendeleyev had predicted, on the basis of the periodic law, that the element exists in nature and that its properties resemble those of the element boron. The element was named after the region of Scandinavia.
Scandium is sometimes regarded as one of the rare earth elements. It occurs in rare minerals such as wolframite. Scandium is about 50th in order of abundance of the elements in Earth's crust. It forms trivalent, colorless salts.
Scandium melts at about 1541°C (about 2806°F), boils at about 2836°C (about 5137°F), and has a specific gravity of 2.99. The atomic weight of scandium is 44.956.
Terbium, symbol Tb, metallic element with an atomic number of 65. Terbium is one of the rare earth elements in the lanthanide series of the periodic table. The elements terbium, erbium, yttrium, and ytterbium were all named for the town of Ytterby in Sweden, the location of a quarry that yielded several rare earth elements.
Terbium was discovered in 1843 by the Swedish chemist Carl Gustav Mosander. It ranks about 58th in natural abundance among the elements in crustal rock. The element occurs in minute quantities as a white oxide known as terbia, Tb2O3, in such minerals as monazite and gadolinite. Terbium has potential applications in alloys, refractory (high-temperature) materials, and electronic apparatus.
Terbium melts at about 1356°C (about 2473°F), boils at about 3230°C (about 5846°F), and has a specific gravity of 8.23. The atomic weight of terbium is 158.925.
Thulium, symbol Tm, silver-gray metallic element that is the rarest of the rare earth elements. Thulium is in the lanthanide series of the periodic table; the atomic number of thulium is 69. The element’s name come from Thule, an ancient Greek name for the northernmost reaches of Europe.
Thulium was discovered in 1879 by the Swedish chemist Per Teodor Cleve. Thulium ranks about 61st in abundance among the elements in Earth’s crust and is found in small quantities in such rare earth minerals as euxenite, gadolinite, and blomstrandine. The metal can be isolated by reduction of its oxide, Tm2O3, and is soft, malleable, and ductile. Thulium had little practical application until the development in the 1950s of a small, portable X-ray machine that utilizes artificially radioactive thulium as its X-ray source.
Thulium melts at about 1545°C (about 2813°F), boils at about 1950°C (about 3542°F), and has a specific gravity of 9.32. The atomic weight of thulium is 168.934.
Tritium, radioactive hydrogen isotope of atomic mass 3 and symbol 1H3 or T. The nucleus of a tritium atom consists of a proton and two neutrons and has a mass of 3.016049. It undergoes decay by beta emission to give a helium nucleus of mass 3; it has a half-life of 12.26 years. Tritium is produced in a number of ways, including the bombardment of deuterium compounds with high-energy deuterons and by the absorption of neutrons by the lithium isotope of mass 6.
Some tritium is produced in the upper levels of the atmosphere by the bombardment of nitrogen with energetic neutrons produced by cosmic rays; rainwater is usually found to contain minute amounts of tritium. The enormous amount of energy released when tritons react with deuterons in the so-called nuclear-fusion process makes tritium an important constituent of hydrogen bombs. Tritium is also used as a tracer in chemical and biochemical research.
Xenon (Greek xenon, “stranger”), symbol Xe, colorless, odorless gaseous element with an atomic number of 54. In group 18 (or VIIIa) of the periodic table, xenon is one of the noble gases.
Xenon was discovered in 1898 by the British chemists Sir William Ramsay and Morris Travers. It was formerly believed to be chemically inert, but since 1962 several compounds of xenon have been prepared. Xenon is used principally in such lighting devices as high-speed photographic tubes. Xenon is present in the atmosphere in minute amounts. The majority of the gas used commercially is produced by fractional distillation of air.
Xenon melts at -111.8°C (-169.2°F) and boils at -108.1°C (-162.6°F). Its density is 5.9 g/liter at 0°C (32°F) and 1 atmosphere pressure and its atomic weight is 131.29.
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