Americium (Am)
Americium (Am) is a radioactive synthetic element with the atomic number 95, classified among the actinides in the periodic table. It resides below europium and between plutonium and curium in the actinide series, which encompasses elements with atomic numbers from 89 to 103. First produced in 1944 by American scientists during the Manhattan Project, americium was derived from bombarding plutonium-239 with neutrons. The element was named after America, reflecting its discovery context. Americium has a shiny silvery-white appearance and exists in solid form at room temperature, with a melting point of 1176°C and a boiling point of 2011°C.
The most stable isotopes of americium are americium-241 and americium-243, both of which have significant half-lives and are used in various applications. Americium-241 is commonly utilized as an ionization source in smoke detectors, valued for being less harmful than radium. Despite its practical uses, americium's highly radioactive nature necessitates careful handling to avoid health risks, making it suitable for use primarily by trained professionals in industries such as healthcare and environmental monitoring.
Subject Terms
Americium (Am)
- Element Symbol: Am
- Atomic Number: 95
- Atomic Mass: 243
- Group # in Periodic Table: n/a
- Group Name: Actinides
- Period in Periodic Table: 7
- Block of Periodic Table: f-block
- Discovered by: Glenn T. Seaborg, Ralph A. James, Leon O. Morgan, Albert Ghiorso (1944)
Americium is a highly radioactive alkali metal whose chemical symbol is Am. It is one of the fifteen metallic elements in the actinide series, which is the sixth group in the periodic table. The atomic numbers in that group range from 89 to 103. The first element in the actinide series, actinium, is the element that gives this group its name; the last element is lawrencium. Americium has an atomic number of 95. In the periodic table, americium is located below europium and between plutonium and curium in row 7, which is the actinide-series row. Because americium falls in this row, its period number is 7. It is also an f-block element, which means it belongs to the group of elements that are called the inner transition elements. This name reflects the position of these elements in the periodic table. Transuranium elements are those whose atomic numbers are larger than that of uranium. Americium is the third transuranium element, although it was the fourth to be discovered after curium, which is the fourth element in the series. Americium was first produced by a team of American scientists; most of them were affiliated with the University of California, Berkeley. The Berkeley team included Glenn T. Seaborg, Ralph A. James, and Leon O. Morgan. Joining them, from the metallurgical laboratory at the University of Chicago, was Albert Ghiorso. Americium was first produced during work on the Manhattan Project when plutonium-239 was bombarded with neutrons in a nuclear reactor. This World War II project was a top-secret effort to develop an atomic bomb. Although the element was first produced in 1944, news of its discovery was kept hidden at first because of the secret nature of the wartime work. When its discovery was finally reported a year later, the announcement included the news that the element had been named after America. Earlier, europium had also been named after the continent where it was discovered. Americium and Europium share several similar physical and chemical properties.
Physical Properties
Americium is a shiny metal with a silvery-white luster. It has an atomic mass of 243, and its standard state at 298 K is solid. The density of americium is 12 grams per cubic centimeter. Its specific gravity is 13.67 grams per cubic centimeter, and its specific heat is 0.11 joules per kilogram. It has a melting point of 1176°C and a boiling point of 2011°C. The thermal conductivity of americium is 10 watts per meter kelvin. It has an electrical conductivity of 0.7 × 106 siemens per meter. Americium is not magnetic. Only at high temperatures does it display superconducting properties. At high pressure, it changes from a high-symmetry cubic structure to an orthorhombic or tetragonal crystal structure. The orthorhombic structure, which is based on three unequal axes that are all at right angles to each other, consists of a seven lattice-point group.
Chemical Properties
Americium has a double hexagonal, close-packed, crystal structure. It reacts slowly with oxygen but dissolves readily in acids. The most common oxidation states of americium are +6, +5, +4, and +3; and the range of the other states is between +2 and +7. Each oxidation state has its characteristic spectrum. Americium’s electron configuration is [Rn]5f<sup>7</sup>7s<sup>2</sup>. The element has an electronegativity of 1.3. Its first ionization energy is 578 kilojoules per mole. Americium has nineteen isotopes, none of which are stable. The element can decay through alpha decay and spontaneous fission. The mass numbers of the isotopes range from 231 to 249. The most common isotopes are americium-241 and americium-243. Its most stable isotope, americium-243, has a half-life of 7,370 years. Americium-241, the first isotope to be isolated, has a half-life of 432 years. The americium-242 isotope has a half-life of about 16 hours. All other isotopes have half-lives of less than 50 hours. The americium-243 isotope is difficult to extract. The americium-243 isotope, on the other hand, is relatively easy to extract, thus making it the most commonly used isotope. Americium is produced from plutonium-239, and it decays into neptunium-237.
Applications
Because Americium is not a naturally occurring element, it has to be synthesized. The most common method of synthesis involves bombarding plutonium with neutrons in nuclear reactors. However, it is often difficult to get a pure form of americium. Different forms of compounds are generated during this bombardment procedure, and these different forms require further processing before the pure form of the element can be extracted. In the early years after its discovery, it was possible to synthesize very small quantities (in milligrams) of the radioactive element. Since then, however, producing larger quantities (in kilograms) has become possible. The element is a strong emitter of alpha particles and gamma rays, and it therefore finds several uses in various industries, such as the glass industry, the oil and natural gas industry, and the health care industry. The americium-241 isotope, in the form of americium dioxide, is used in extremely small quantities as an ionization source in domestic smoke detectors. Americium is preferred over radium in these devices because it is the less harmful of the two elements. Americium also has uses in spectroscopy. Due to the highly radioactive nature of americium, exposure can pose great health risks. Extreme care should be taken to ensure that it is handled only by experts who are taking the necessary precautions.
Bibliography
"Americium." Periodic Table. Royal Society of Chemistry, 2015. Web. 28 Sept. 2015. <www.rsc.org/periodic-table/element/95/americium>.
"Americium." Periodic Table. Wolfram Research, 2015. Web. 28 Sept. 2015. <http://periodictable.com/Elements/095/index.html>.
Editors of Encyclopaedia Britannica. "Americium (Am)." Encyclopaedia Britannica. Encyclopaedia Britannica Inc., 2015. Web. 28 Sept. 2015. <https://www.britannica.com/science/americium>.
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