Curium
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| Name, Symbol, Number | curium, Cm, 96 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Chemical series | actinides | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Group, Period, Block | n/a, 7, f | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Appearance | silvery | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Atomic mass | (247) g/mol | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Electron configuration | [Rn] 5f7 6d1 7s2 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Electrons per shell | 2, 8, 18, 32, 25, 9, 2 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Physical properties | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Phase | solid | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Density (near r.t.) | 13.51 g/cm³ | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Melting point | 1613 K (1340 °C, 2444 °F) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Boiling point | 3383 K (3110 °C, 5630 °F) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Heat of fusion | ? 15 kJ/mol | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Atomic properties | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Crystal structure | hexagonal close-packed | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Oxidation states | 3 (amphoteric oxide) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Electronegativity | 1.3 (Pauling scale) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Ionization energies | 1st: 581 kJ/mol | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Miscellaneous | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Magnetic ordering | no data | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| CAS registry number | 7440-51-9 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Notable isotopes | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Curium (chemical symbol Cm, atomic number 96) is a synthetic chemical element. A radioactive metallic transuranic element of the actinide series, curium is produced by bombarding plutonium with alpha particles (helium ions) and was named after Marie Curie and her husband Pierre.
History
Curium was first synthesized at the University of California, Berkeley by Glenn T. Seaborg, Ralph A. James, and Albert Ghiorso in 1944. The team named the new element after Marie Curie and her husband Pierre who are famous for discovering radium and for their work in radioactivity. It was chemically identified at the Metallurgical Laboratory (now Argonne National Laboratory) at the University of Chicago. It was actually the third transuranium element to be discovered even though it is the second in the series. Curium-242 (half-life 163 days) and one free neutron were made by bombarding alpha particles onto a plutonium-239 target in the 60-inch cyclotron at Berkeley. Louis Werner and Isadore Perlman created a visible sample of curium-242 hydroxide at the University of California in 1947 by bombarding americium-241 with neutrons. Curium was made in its elemental form in 1951 for the first time.
Notable characteristics
Curium is an inner transition metal (or actinide) that lies in period 7 of the periodic table, between americium and berkelium.
The isotope curium-248 has been synthesized only in milligram quantities, but curium-242 and curium-244 are made in multigram amounts, which allows for the determination of some of the element's properties. Curium-244 can be made in quantity by subjecting plutonium to neutron bombardment. Curium does not occur in nature. There are few commercial applications, for curium but it may one day be useful in radioisotope thermoelectric generators. Curium bio-accumulates in bone tissue where its radiation destroys bone marrow and thus stops red blood cell creation.
A rare earth homolog, curium is somewhat chemically similar to gadolinium but with a more complex crystal structure. Chemically reactive, its metal is silvery-white in color and the element is more electropositive than aluminium (most trivalent curium compounds are slightly yellow).
Curium has been studied greatly as a potential fuel for Radioisotope thermoelectric generators. Curium-242 can generate up to 120 watts of thermal energy per gram (W/g); its very short half-life though makes it undesirable as a power source for long-term use. Curium-242 is the precursor to plutonium-238 which is the most common fuel for RTGs. Curium-244 has also been studied as an energy source for RTGs having a maximum energy density ~3 W/g, but produces a large amount of neutron radiation from spontaneous fission. Curium-243 with a ~30 year half-life and good energy density of ~1.6 W/g would seem to make an ideal fuel, but it produces significant amounts of gamma and beta radiation from radioactive decay products.
Isotopes
Many radioisotopes of curium have been characterized, with the most stable being Cm-247 with a half-life of 1.56 × 107 years, Cm-248 with a half-life of 3.40 × 105 years, Cm-250 with a half-life of 9000 years, and Cm-245 with a half-life of 8500 years. All of the remaining radioactive isotopes have half-lifes that are less than 30 years, and the majority of these have half lifes that are less than 33 days. This element also has 4 meta states, with the most stable being Cm-244m (t½ 34 ms). The isotopes of curium range in atomic weight from 233.051 u (Cm-233) to 252.085 u (Cm-252).
Compounds
Known compounds of curium include the following:
- Oxides:
- curium dioxide (CmO2)
- curium trioxide (Cm2O3)
- Halides:
Nuclear fuel cycle
The MOX which is to be used in power reactors should contain little or no curium as the neutron activation of this element will create californium which is a strong neutron emitter. The californium would pollute the back end of the fuel cycle and increase the dose to workers. Hence if the Minor actinides are to be used as fuel in a thermal neutron reactor the curium should be excluded from the fuel or placed in special fuel rods where it is the only actinide present.
See also
ReferencesISBN links support NWE through referral fees
- Emsley, John. 2001. Nature's Building Blocks: An A–Z Guide to the Elements. Oxford: Oxford Univ. Press. ISBN 0198503407 and ISBN 978-0198503408.
- Greenwood, N.N., and A. Earnshaw. 1998. Chemistry of the Elements 2nd ed. Oxford, UK; Burlington, MA: Butterworth-Heinemann. ISBN 0750633654. Online version.
- Hampel, Clifford A. 1968. The Encyclopedia of the Chemical Elements. New York: Reinhold Book Corp. ISBN 0442155980 and ISBN 978-0442155988.
- Morss, Lester R., Norman M. Edelstein, and Jean Fuger, eds. 2006. The Chemistry of the Actinide and Transactinide Elements. 3rd ed. 5 vols. Joseph J. Katz, adapter. Dordrecht: Springer. ISBN 1402035551 and ISBN 978-1402035555.
- Stwertka, Albert. 1998. Guide to the Elements. Rev. ed. Oxford: Oxford University Press. ISBN 0-19-508083-1.
- Chemistry Operations. 2003. "Curium" Los Alamos National Laboratory, Chemistry Division. Retrieved March 14, 2007.
External links
- It's Elemental - Curium
- Human Health Fact Sheet on Curium
- WebElements.com - Curium
- NLM Hazardous Substances Databank – Curium, Radioactive
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