|
Actinoid Contraction
The actinide contraction is the greater-than-expected decrease in atomic radii and ionic radii of the elements in the actinide series, from left to right. Description It is more pronounced than the lanthanide contraction because the 5f electrons are less effective at shielding than 4f electrons. It is caused by the poor shielding effect of nuclear charge by the 5f electrons along with the expected periodic trend of increasing electronegativity and nuclear charge on moving from left to right. About 40-50% of the actinide contraction has been attributed to relativistic effects. A decrease in atomic radii can be observed across the 5f elements from atomic number 89, actinium, to 102, nobelium. This results in smaller than otherwise expected atomic radii and ionic radii for the subsequent d-block elements starting with 103, lawrencium. Jolly, William L. ''Modern Inorganic Chemistry'', McGraw-Hill 1984, p. 22 This effect causes the radii of transition metals of group 5 and 6 to b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atomic Radii
The atomic radius of a chemical element is a measure of the size of its atom, usually the mean or typical distance from the center of the nucleus to the outermost isolated electron. Since the boundary is not a well-defined physical entity, there are various non-equivalent definitions of atomic radius. Four widely used definitions of atomic radius are: Van der Waals radius, ionic radius, metallic radius and covalent radius. Typically, because of the difficulty to isolate atoms in order to measure their radii separately, atomic radius is measured in a chemically bonded state; however theoretical calculations are simpler when considering atoms in isolation. The dependencies on environment, probe, and state lead to a multiplicity of definitions. Depending on the definition, the term may apply to atoms in condensed matter, covalently bonding in molecules, or in ionized and excited states; and its value may be obtained through experimental measurements, or computed from theoretical m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radon
Radon is a chemical element; it has symbol Rn and atomic number 86. It is a radioactive noble gas and is colorless and odorless. Of the three naturally occurring radon isotopes, only Rn has a sufficiently long half-life (3.825 days) for it to be released from the soil and rock where it is generated. Radon isotopes are the immediate decay products of radium isotopes. The instability of Rn, its most stable isotope, makes radon one of the rarest elements. Radon will be present on Earth for several billion more years despite its short half-life, because it is constantly being produced as a step in the decay chains of U and Th, both of which are abundant radioactive nuclides with half-lives of at least several billion years. The decay of radon produces many other short-lived nuclides, known as "radon daughters", ending at stable isotopes of lead. Rn occurs in significant quantities as a step in the normal radioactive decay chain of U, also known as the uranium series, which slo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mendelevium
Mendelevium is a synthetic chemical element; it has symbol Md ( formerly Mv) and atomic number 101. A metallic radioactive transuranium element in the actinide series, it is the first element by atomic number that currently cannot be produced in macroscopic quantities by neutron bombardment of lighter elements. It is the third-to-last actinide and the ninth transuranic element and the first transfermium. It can only be produced in particle accelerators by bombarding lighter elements with charged particles. Seventeen isotopes are known; the most stable is 258Md with half-life 51.59 days; however, the shorter-lived 256Md (half-life 77.7 minutes) is most commonly used in chemistry because it can be produced on a larger scale. Mendelevium was discovered by bombarding einsteinium with alpha particles in 1955, the method still used to produce it today. It is named after Dmitri Mendeleev, the father of the periodic table. Using available microgram quantities of e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fermium
Fermium is a synthetic chemical element; it has symbol Fm and atomic number 100. It is an actinide and the heaviest element that can be formed by neutron bombardment of lighter elements, and hence the last element that can be prepared in macroscopic quantities, although pure fermium metal has not been prepared yet. A total of 20 isotopes are known, with 257Fm being the longest-lived with a half-life of 100.5 days. Fermium was discovered in the debris of the first hydrogen bomb explosion in 1952, and named after Enrico Fermi, one of the pioneers of nuclear physics. Its chemistry is typical for the late actinides, with a preponderance of the +3 oxidation state but also an accessible +2 oxidation state. Owing to the small amounts of produced fermium and all of its isotopes having relatively short half-lives, there are currently no uses for it outside basic scientific research. Discovery Fermium was first discovered in the fallout from the 'Ivy Mike' nuclear test (1 Nove ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Einsteinium
Einsteinium is a synthetic chemical element; it has 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 first hydrogen bomb explosion in 1952. Its most common isotope, einsteinium-253 (Es; half-life 20.47 days), is produced artificially from decay of californium-253 in a few dedicated high-power nuclear reactors 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 synthesiz ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Californium
Californium is a synthetic chemical element; it has symbol Cf and atomic number 98. It was first synthesized in 1950 at Lawrence Berkeley National Laboratory (then the University of California Radiation Laboratory) by bombarding curium with alpha particles (helium-4 ions). It is an actinide element, the sixth transuranium element to be synthesized, and has the second-highest atomic mass of all elements that have been produced in amounts large enough to see with the naked eye (after einsteinium). It was named after the university and the U.S. state of California. Two crystalline forms exist at normal pressure: one above and one below . A third form exists at high pressure. Californium slowly tarnishes in air at room temperature. Californium compounds are dominated by the +3 oxidation state. The most stable of californium's twenty known isotopes is californium-251, with a half-life of 898 years. This short half-life means the element is not found in significant quantities in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Berkelium
Berkelium is a synthetic chemical element; it has symbol Bk and atomic number 97. It is a member of the actinide and transuranium element series. It is named after the city of Berkeley, California, the location of the Lawrence Berkeley National Laboratory (then the University of California Radiation Laboratory) where it was discovered in December 1949. Berkelium was the fifth transuranium element discovered after neptunium, plutonium, curium and americium. The major isotope of berkelium, 249Bk, is synthesized in minute quantities in dedicated high-flux nuclear reactors, mainly at the Oak Ridge National Laboratory in Tennessee, United States, and at the Research Institute of Atomic Reactors in Dimitrovgrad, Russia. The longest-lived and second-most important isotope, 247Bk, can be synthesized via irradiation of 244Cm with high-energy alpha particles. Just over one gram of berkelium has been produced in the United States since 1967. There is no practical application of berkeli ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Curium
Curium is a synthetic chemical element; it has symbol Cm and atomic number 96. This transuranic actinide element was named after eminent scientists Marie and Pierre Curie, both known for their research on radioactivity. Curium was first intentionally made by the team of Glenn T. Seaborg, Ralph A. James, and Albert Ghiorso in 1944, using the cyclotron at Berkeley. They bombarded the newly discovered element plutonium (the isotope 239Pu) with alpha particles. This was then sent to the Metallurgical Laboratory at University of Chicago where a tiny sample of curium was eventually separated and identified. The discovery was kept secret until after the end of World War II. The news was released to the public in November 1947. Most curium is produced by bombarding uranium or plutonium with neutrons in nuclear reactors – one tonne of spent nuclear fuel contains ~20 grams of curium. Curium is a hard, dense, silvery metal with a high melting and boiling point for an actinide. It ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Americium
Americium is a synthetic element, synthetic chemical element; it has Chemical symbol, symbol Am and atomic number 95. It is radioactive and a transuranic member of the actinide series in the periodic table, located under the lanthanide element europium and was thus named after the Americas by analogy. Americium was first produced in 1944 by the group of Glenn T. Seaborg from Berkeley, California, at the Metallurgical Laboratory of the University of Chicago, as part of the Manhattan Project. Although it is the third element in the transuranic series, it was discovered fourth, after the heavier curium. The discovery was kept secret and only released to the public in November 1945. Most americium is produced by uranium or plutonium being bombarded with neutrons in nuclear reactors – one tonne of spent nuclear fuel contains about 100 grams of americium. It is widely used in commercial ionization chamber smoke detectors, as well as in neutron sources and industrial gauges. Several u ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plutonium
Plutonium is a chemical element; it has symbol Pu and atomic number 94. It is a silvery-gray actinide metal that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation states. It reacts with carbon, halogens, nitrogen, silicon, and hydrogen. When exposed to moist air, it forms oxides and hydrides that can expand the sample up to 70% in volume, which in turn flake off as a powder that is pyrophoric. It is radioactive and can accumulate in bones, which makes the handling of plutonium dangerous. Plutonium was first synthesized and isolated in late 1940 and early 1941, by deuteron bombardment of uranium-238 in the cyclotron at the University of California, Berkeley. First, neptunium-238 (half-life 2.1 days) was synthesized, which then beta-decayed to form the new element with atomic number 94 and atomic weight 238 (half-life 88 years). Since uranium had been named after the planet Uranus ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Neptunium
Neptunium is a chemical element; it has chemical symbol, symbol Np and atomic number 93. A radioactivity, radioactive actinide metal, neptunium is the first transuranic element. It is named after Neptune, the planet beyond Uranus in the Solar System, which uranium is named after. A neptunium atom has 93 protons and 93 electrons, of which seven are valence electrons. Neptunium metal is silvery and tarnishes when exposed to air. The element occurs in three allotrope, allotropic forms and it normally exhibits five oxidation states, ranging from +3 to +7. Like all actinides, it is Radioactive decay, radioactive, radiation poisoning, poisonous, pyrophoricity, pyrophoric, and capable of accumulating in bones, which makes the handling of neptunium dangerous. Although many false claims of its discovery were made over the years, the element was first synthesized by Edwin McMillan and Philip H. Abelson at the Berkeley Radiation Laboratory in 1940. Since then, most neptunium has been and still ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Uranium
Uranium is a chemical element; it has chemical symbol, symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium radioactive decay, radioactively decays, usually by emitting an alpha particle. The half-life of this decay varies between 159,200 and 4.5 billion years for different isotopes of uranium, isotopes, making them useful for dating the age of the Earth. The most common isotopes in natural uranium are uranium-238 (which has 146 neutrons and accounts for over 99% of uranium on Earth) and uranium-235 (which has 143 neutrons). Uranium has the highest atomic weight of the primordial nuclide, primordially occurring elements. Its density is about 70% higher than that of lead and slightly lower than that of gold or tungsten. It occurs naturally in low concentrations of a few Parts-per notation#Parts-per expressions, parts per million in soil, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
