Americium

Americium, 95Am
Americium
Pronunciation/ˌæməˈrɪsiəm/ ​(AM-ə-RISS-ee-əm)
Appearancesilvery white
Mass number[243]
Americium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Eu
↑
Am
↓
—
plutonium ← americium → curium
Atomic number (Z)95
Groupf-block groups (no number)
Periodperiod 7
Block  f-block
Electron configuration[Rn] 5f7 7s2
Electrons per shell2, 8, 18, 32, 25, 8, 2
Physical properties
Phase at STPsolid
Melting point1449 K ​(1176 °C, ​2149 °F)
Boiling point2880 K ​(2607 °C, ​4725 °F) (calculated)
Density (near r.t.)12 g/cm3
Heat of fusion14.39 kJ/mol
Molar heat capacity28[1] J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 1239 1356
Atomic properties
Oxidation statescommon: +3
+2,[2] +4,[2] +5,[2] +6,[2] +7
ElectronegativityPauling scale: 1.3
Ionization energies
  • 1st: 578 kJ/mol
Atomic radiusempirical: 173 pm
Covalent radius180±6 pm
Color lines in a spectral range
Spectral lines of americium
Other properties
Natural occurrencesynthetic
Crystal structure ​double hexagonal close-packed (dhcp)
Double hexagonal close packed crystal structure for americium
Thermal conductivity10 W/(m⋅K)
Electrical resistivity0.69 µΩ⋅m[1]
Magnetic orderingparamagnetic
Molar magnetic susceptibility+1000.0×10−6 cm3/mol[3]
CAS Number7440-35-9
History
Namingafter the Americas
DiscoveryGlenn T. Seaborg, Ralph A. James, Leon O. Morgan, Albert Ghiorso (1944)
Isotopes of americium
Main isotopes[4] Decay
abun­dance half-life (t1/2) mode pro­duct
241Am synth 432.2 y α 237Np
SF –
242m1Am synth 141 y IT 242Am
α 238Np
SF –
243Am synth 7350 y α 239Np
SF –
 Category: Americium
| references

Americium is a synthetic chemical element; it has 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.[5][6][7]

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 unusual applications, such as nuclear batteries or fuel for space ships with nuclear propulsion, have been proposed for the isotope 242mAm, but they are as yet hindered by the scarcity and high price of this nuclear isomer.

Americium is a relatively soft radioactive metal with a silvery appearance. Its most common isotopes are 241Am and 243Am. In chemical compounds, americium usually assumes the oxidation state +3, especially in solutions. Several other oxidation states are known, ranging from +2 to +7, and can be identified by their characteristic optical absorption spectra. The crystal lattices of solid americium and its compounds contain small intrinsic radiogenic defects, due to metamictization induced by self-irradiation with alpha particles, which accumulates with time; this can cause a drift of some material properties over time, more noticeable in older samples.

  1. ^ a b Muller, W.; Schenkel, R.; Schmidt, H. E.; Spirlet, J. C.; McElroy, D. L.; Hall, R. O. A.; Mortimer, M. J. (1978). "The electrical resistivity and specific heat of americium metal". Journal of Low Temperature Physics. 30 (5–6): 561. Bibcode:1978JLTP...30..561M. doi:10.1007/BF00116197.
  2. ^ a b c d Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 28. ISBN 978-0-08-037941-8.
  3. ^ Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.
  4. ^ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
  5. ^ Seaborg, Glenn T. (1946). "The Transuranium Elements". Science. 104 (2704): 379–386. Bibcode:1946Sci...104..379S. doi:10.1126/science.104.2704.379. JSTOR 1675046. PMID 17842184.
  6. ^ Kostecka, Keith (2008). "Americium – From Discovery to the Smoke Detector and Beyond" (PDF). Bull. Hist. Chem. 33 (2): 89–93. Archived (PDF) from the original on 9 October 2022.
  7. ^ "C&En: It's Elemental: The Periodic Table - Americium".