Curium (Cm)
actinideSolid
Peso atomico standard
[247]Configurazione elettronica
[Rn] 7s2 5f7 6d1Punto di fusione
1344,85 °CPunto di ebollizione
3126,85 °CDensità
1,351e+4 kg/m³Stati di ossidazione
+3, +4, +5, +6Elettronegatività (Pauling)
1,3Energia di ionizzazione (1ª)
5,992241 eVAnno della scoperta
1944Raggio atomico
N/DDettagli
Curium is a synthetic transuranium actinide named for Marie and Pierre Curie. It is produced in nuclear reactors by successive neutron capture in plutonium and americium, and all of its isotopes are radioactive. Chemically it is a typical later actinide, dominated by the +3 oxidation state in water and by compounds resembling those of americium and the lanthanides. Its most important practical feature is the intense alpha emission of selected isotopes, especially ²⁴⁴Cm.
Curium does not occur naturally in the Earth’s crust. It was first synthesized in 1944 by Glenn T. Seaborg and his team at the University of California in Berkeley using the reaction 239Pu (4He, n) 242Cm. The element was named after Pierre and Marie Curie, who discovered radium and polonium.
Minute amounts of curium probably exist in natural deposits of uranium, as a result of a sequence of neutron captures and beta decays sustained by the very low flux of neutrons naturally present in uranium ores. The presence of natural curium, however, has never been detected. 242Cm and 244Cm are available in multigram quantities. 248Cm has been produced only in milligram amounts. Curium is similar in some regards to gadolinium, its rare earth homolog, but it has a more complex crystal structure. Curium metal is lustrous, malleable, silver in color, chemically reactive, and is more electropositive than aluminum. Curium metal exist in two crystal forms, a double hexagonal close packed (dhcp) and a high temperature face-centered cubic close packed (fcc) structure. Metallic curium dissolves rapidly in dilute acid to form Cm(III) solutions. Curium metal surfaces rapidly oxidize in air to form a thin film possibly starting out as CmO, Oxidation then progressing to Cm2O3, and eventually to form stable CmO2. Note however that the formation of divalent compounds of curium such as CmO have never been observed in bulk form. Most compounds and solutions of trivalent curium are quite stable and are faintly yellow or yellow-green in color. The stability of the trivalent state for curium is attributed to the half-filled 5f7 electron shell configuration. Curium in the tetravalent state is meta-stable in concentrated fluoride solutions but very stable in the solid state, primarily as the oxides and fluorides. Because curium isotopes are available in macro quantities a number of curium compounds have been prepared and characterized with the majority in the trivalent state.
242Cm generates about three watts of thermal energy per gram. This compares to one-half watt per gram of 238Pu. Both 242Cm and 244Cm have been used as power sources for space and medical uses. 244Cm is now offered for sale at $100/mg. Curium absorbed into the body accumulates in the bones, and is therefore very toxic as its radiation destroys the red-cell forming mechanism. The maximum permissible total body burden of 244Cm (soluble) in a human being is 0.3 microcurie.
This element reviewed and Updated by Dr. David Hobart, 2011
Curium was first produced by Glenn T. Seaborg, Ralph A. James and Albert Ghiorso, working at the University of California, Berkeley, in 1944. They bombarded atoms of plutonium-239, an isotope of plutonium, with alpha particles that had been accelerated in a device called a cyclotron. This produced atoms of curium-242 and one free neutron. Curium-242 has a half-life of about 163 days and decays into plutonium-238 through alpha decay or decays through spontaneous fission. Curium's most stable isotope, curium-247, has a half-life of about 15,600,000 years. It decays into plutonium-243 through alpha decay.
Although curium follows americium in the periodic system, it was actually the third transuranium element to be discovered. It was identified by Seaborg, James, and Ghiorso in 1944 at the wartime metallurgical laboratory at the University of Chicago as a result of helium-ion bombardment of 239Pu in the Berkeley, California, 60-inch cyclotron. Visible amounts (30 µg) of 242Cm, in the form of the hydroxide, were first isolated by Werner and Perlman of the University of California in 1947. In 1950, Crane, Wallmann, and Cunningham found that the magnetic susceptibility of microgram samples of CmF3 was of the same magnitude as that of GdF3. This provided direct experimental evidence for assigning an electronic configuration to Cm+3. In 1951, the same workers prepared curium in its elemental form for the first time. Fourteen isotopes of curium are now known ranging in mass from 237 to 251. The most stable, 247Cm, with a half-life of 16 million years, is so short compared to the earth's age that any primordial curium must have disappeared long ago from the natural scene.
Curium has been prepared as a metallic element in small amounts. The metal is described as silvery and lustrous when freshly prepared, but it is highly radioactive and self-heating in appreciable quantities. Handling is normally confined to sealed or shielded laboratory forms rather than visible bulk pieces.
Curium has no broad commercial use as an element. ²⁴⁴Cm and related isotopes are used as compact alpha-particle sources, most notably in alpha particle X-ray spectrometers that determine the elemental composition of rocks and soils on planetary missions. Curium also serves as a target material for producing heavier actinides and transactinide elements in research reactors and particle accelerators. Some isotope heat-source applications have been investigated, but they are not a general industrial use.
Since only milligram amounts of curium have ever been produced, there are currently no commercial applications for it, although it might be used in radioisotope thermoelectric generators in the future. Curium is primarily used for basic scientific research.
Scientists have produced several curium compounds. They include: curium dioxide (CmO2), curium trioxide (Cm2O3), curium bromide (CmBr3), curium chloride (CmCl3), curium chloride (CmCl3), curium tetrafluoride (CmF4) and curium iodide (CmI3). As with the element, the compounds currently have no commercial applications and are primarily used for basic scientific research.
Isotopes in Industry
244Cm and 242Cm (with half-lives of 18.1 years and 163 days, respectively) are strong alpha emitters (see alpha decay). The alpha emission from these isotopes creates a considerable quantity of heat that makes them useful as alpha particle sources, as well as heat generators in RTGs (radioisotopic thermoelectric generators) [75] J. Peterson, M. McDonell, L. Haroun, F. Monette, R. D. Hildebrand, A. Taboas. Radiological and Chemical Fact Sheets to Support Health Risk Analyses for Contaminated Areas, Prepared by Argonne National Laboratory Environmental Science Division in collaboration with U.S. Department of Energy, Richland Operations Office and Chicago Operations Office (2014), Feb. 22; http://www.remm.nlm.gov/ANL_ContaminantFactSheets_All_070418.pdf.. During a number of space missions based in America and Europe, 244Cm was the source used for the alpha particle X-ray spectrometer that was on board vehicles such as the Mars Exploration Rover and the Rosetta/Philae [75] J. Peterson, M. McDonell, L. Haroun, F. Monette, R. D. Hildebrand, A. Taboas. Radiological and Chemical Fact Sheets to Support Health Risk Analyses for Contaminated Areas, Prepared by Argonne National Laboratory Environmental Science Division in collaboration with U.S. Department of Energy, Richland Operations Office and Chicago Operations Office (2014), Feb. 22; http://www.remm.nlm.gov/ANL_ContaminantFactSheets_All_070418.pdf., [618] Royal Australian Chemical Institute. Curium, Royal Australian Chemical Institute (2016), October 10; http://www.rsc.org/periodic-table/element/96/curium.. 244Cm has a large neutron capture to neutron fission cross-section ratio and has been used in a nuclear reactor to produce higher mass radio-isotopes of curium (Fig. IUPAC.96.1) [75] J. Peterson, M. McDonell, L. Haroun, F. Monette, R. D. Hildebrand, A. Taboas. Radiological and Chemical Fact Sheets to Support Health Risk Analyses for Contaminated Areas, Prepared by Argonne National Laboratory Environmental Science Division in collaboration with U.S. Department of Energy, Richland Operations Office and Chicago Operations Office (2014), Feb. 22; http://www.remm.nlm.gov/ANL_ContaminantFactSheets_All_070418.pdf., [618] Royal Australian Chemical Institute. Curium, Royal Australian Chemical Institute (2016), October 10; http://www.rsc.org/periodic-table/element/96/curium..
Curium chemistry is centered on Cm³⁺ in aqueous solution, where its salts often show strong orange to yellow luminescence useful in spectroscopic studies. Representative compounds include curium(III) oxide, Cm₂O₃, curium dioxide, CmO₂, curium(III) fluoride, CmF₃, and curium(III) chloride, CmCl₃. The +4 state is accessible in some solids such as dioxide and fluoride systems, but it is less stable in ordinary aqueous chemistry. Higher oxidation states have been reported only under specialized conditions and are not central to curium chemistry.
See more information at the Curium compound page.
Curium is a severe radiological hazard. Most accessible isotopes emit alpha particles, which are readily stopped outside the body but dangerous if curium is inhaled, ingested, or enters wounds. Some isotopes and decay products also produce gamma radiation or neutrons, especially where spontaneous fission is significant. Milligram quantities can generate noticeable heat. Work requires contamination control, shielding appropriate to the isotope mixture, and remote handling for larger sources.
Curium is not a naturally cycling element in any significant sense. Trace amounts can be formed in nuclear explosions, reactor fuel, and other intense neutron fields, and it occurs in spent nuclear fuel and high-level waste. In the environment it tends to bind strongly to mineral surfaces, organic matter, and fine particles, while its mobility depends on acidity, complexing ligands, and redox conditions. Its ecological significance is mainly radiological rather than nutritional or geochemical.
Curium has no commodity market. It is obtained only in specialized nuclear programs by irradiating actinide targets, followed by difficult radiochemical separation from chemically similar transuranium elements and fission products. Supply is constrained by reactor capacity, target availability, isotope purity requirements, heat generation, and radiation shielding. Recovered curium is allocated mainly to research, source fabrication, and production of heavier elements. Recycling is possible within nuclear laboratories but is not comparable to industrial metal recycling.
Made by bombarding plutonium with helium ions. So radioactive it glows in the dark.
Curium is not a primordial cosmic element because all known isotopes have half-lives far shorter than the age of the Solar System. It can be made in very small amounts by rapid neutron-capture processes in extreme astrophysical events, but any such curium decays away on geological timescales. Present curium in the Solar System is therefore artificial, apart from possible transient atoms in unusual natural nuclear environments.
- ²⁴⁴Cm is a common laboratory curium isotope because it combines useful alpha emission with a manageable half-life.
- Curium’s strong radioactivity can damage its own crystal lattice over time.
- The element was first identified during wartime transuranium research before it was publicly announced.
- Curium targets have been used in attempts to synthesize still heavier elements.
- Cm³⁺ luminescence is unusually useful for studying actinide coordination chemistry.
Immagini
Proprietà
Fisiche
- Raggio covalente
- 169 pm Confronta Raggio covalente di tutti gli elementi →
- Raggio di van der Waals
- 245 pm Confronta Raggio di van der Waals di tutti gli elementi →
- Densità
- 1,351 × 104 kg/m³ Confronta Densità di tutti gli elementi →
- Volume molare
- 0,01828 L/mol
- Fase in condizioni STP
- Solido Confronta Fase in condizioni STP di tutti gli elementi →
- Punto di fusione
- 1344,85 °C Confronta Punto di fusione di tutti gli elementi →
- Punto di ebollizione
- 3126,85 °C Confronta Punto di ebollizione di tutti gli elementi →
Chimiche
- Elettronegatività (Pauling)
- 1,3 Confronta Elettronegatività (Pauling) di tutti gli elementi →
- Affinità elettronica
- 0,277 eV
- Energia di ionizzazione (1ª)
- 5,992241 eV Confronta Energia di ionizzazione (1ª) di tutti gli elementi →
- Energia di ionizzazione (2ª)
- 12,400043 eV Confronta Energia di ionizzazione (2ª) di tutti gli elementi →
- Energia di ionizzazione (3ª)
- 20,100069 eV Confronta Energia di ionizzazione (3ª) di tutti gli elementi →
- Energia di ionizzazione (4ª)
- 37,70013 eV Confronta Energia di ionizzazione (4ª) di tutti gli elementi →
- Energia di ionizzazione (5ª)
- 51,000176 eV Confronta Energia di ionizzazione (5ª) di tutti gli elementi →
- Stati di ossidazione
- +3, +4, +5, +6 Confronta Stati di ossidazione di tutti gli elementi →
- Elettroni di valenza
- 3 Confronta Elettroni di valenza di tutti gli elementi →
- Configurazione elettronica
- [Rn] 7s2 5f7 6d1
Termodinamiche
- Calore di sublimazione
- 4,145722 eV
- Calore di atomizzazione
- 4,145722 eV
- Entalpia di atomizzazione
- 4,000622 eV
Nucleari
- Protoni
- 96 Confronta Protoni di tutti gli elementi →
- Neutroni
- 151 Confronta Neutroni di tutti gli elementi →
- Isotopi noti
- 22 Confronta Isotopi noti di tutti gli elementi →
- Isotopi stabili
- 0 Confronta Isotopi stabili di tutti gli elementi →
- Numero di massa (isotopo più stabile)
- 247
- Isotopo più stabile
- Cm-247
- Anno della scoperta
- 1944
Abbondanza
N/D
Struttura cristallina
N/D
Struttura elettronica
- Elettroni per guscio
- 2, 8, 18, 32, 25, 9, 2 Confronta Elettroni per guscio di tutti gli elementi →
Identificativi
- Numero CAS
- 7440-51-9 Confronta Numero CAS di tutti gli elementi →
- Simbolo di termine
- 9D°2
- InChI
- InChI=1S/Cm
- Chiave InChI
- NIWWFAAXEMMFMS-UHFFFAOYSA-N
Configurazione elettronica Misurato
Cm: 5f⁷ 6d¹ 7s²[Rn] 5f⁷ 6d¹ 7s²1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f¹⁴ 5d¹⁰ 6s² 6p⁶ 5f⁷ 6d¹ 7s²Modello atomico
Gli isotopi modificano il numero di neutroni, la massa e la stabilità — non la configurazione elettronica di un atomo neutro.
Modello atomico schematico, non in scala.
Impronta atomica
Spettro di emissione / assorbimento
Distribuzione isotopica
Nessun isotopo stabile.
| Numero di massa | Massa atomica (u) | Abbondanza naturale | Emivita |
|---|---|---|---|
| 250 Radioattivo | 250,078358 ± 0,000012 | N/D | 8300 anni |
| 248 Radioattivo | 248,0723499 ± 0,0000056 | N/D | 348 ky |
| 242 Radioattivo | 242,058836 ± 0,0000019 | N/D | 162.8 giorni |
| 249 Radioattivo | 249,0759548 ± 0,0000056 | N/D | 64.15 minuti |
| 234 Radioattivo | 234,05016 ± 0,00002 | N/D | 52 secondi |
Fase / Stato
Motivo: 3101,8 °C sotto il punto di sublimazione (3126,85 °C)
Schema non in scala
Punti di transizione di fase
Energie di transizione
Energia necessaria per sublimare 1 mol al punto di sublimazione
Densità
In condizioni standard
In condizioni standard
Spettri atomici
Sono visualizzati 10 di 96. Ordinamento per carica ionica crescente.
Righe disponibili ?
| Ione | Carica | Righe totali | Probabilità di transizione | Designazioni dei livelli |
|---|---|---|---|---|
| Cm I | 0 | 140 | 0 | 0 |
| Cm II | +1 | 32 | 0 | 0 |
Livelli disponibili ?
| Ione | Carica | Livelli |
|---|---|---|
| Cm I | 0 | 2 |
| Cm II | +1 | 2 |
| Cm III | +2 | 2 |
| Cm IV | +3 | 2 |
| Cm V | +4 | 2 |
| Cm VI | +5 | 2 |
| Cm VII | +6 | 2 |
| Cm VIII | +7 | 2 |
| Cm IX | +8 | 2 |
| Cm X | +9 | 2 |
Dati sulla struttura cristallina non disponibili
Raggi ionici
| Carica | Coordinazione | Spin | Raggio |
|---|---|---|---|
| +3 | 6 | N/D | 97 pm |
| +3 | 9 | N/D | 114.7 pm |
| +4 | 6 | N/D | 85 pm |
| +4 | 8 | N/D | 95 pm |
Composti
Isotopi (5)
| Numero di massa | Massa atomica (u) | Abbondanza naturale | Emivita | Modalità di decadimento | |
|---|---|---|---|---|---|
| 250 Radioattivo | 250,078358 ± 0,000012 | N/D | 8300 anni | SF ≈74%α ?β- ? | |
| 248 Radioattivo | 248,0723499 ± 0,0000056 | N/D | 348 ky | α =91.61±1.6%SF =8.39±1.6%2β- ? | |
| 242 Radioattivo | 242,058836 ± 0,0000019 | N/D | 162.8 giorni | α =100%SF =6.2e-6±0.3%34Si =1.1e-14±0.4% | |
| 249 Radioattivo | 249,0759548 ± 0,0000056 | N/D | 64.15 minuti | β- =100% | |
| 234 Radioattivo | 234,05016 ± 0,00002 | N/D | 52 secondi | β+ ≈71%α ≈27%SF ≈2% |
Proprietà estese
Raggi covalenti (dati estesi)
- Raggio covalente (Pyykkö)
- 166 pm
- Raggio covalente (Pyykkö, legame doppio)
- 136 pm
Raggi di van der Waals
- Alvarez
- 305 pm
- UFF
- 332,6 pm
Raggi atomici e metallici
- Raggio atomico (Rahm)
- 276 pm
Scale di numerazione
- Mendeleev
- 28
- Pettifor
- 41
- Glawe
- 40
Scale di elettronegatività
- Ghosh
- 0
Polarizzabilità e dispersione
- Polarizzabilità dipolare
- 144 a.u.
- Polarizzabilità dipolare (inc.)
- 25 a.u.
Transizioni di fase e allotropi
| Punto di fusione | 1618,15 K |
Categorie degli stati di ossidazione
Dati di riferimento avanzati
Dettaglio dei raggi cristallini (4)
| Carica | CN | Spin | rcrystal (pm) | Origine |
|---|---|---|---|---|
| 3 | VI | 111 | from r^3 vs V plots, | |
| 4 | VI | 99 | from r^3 vs V plots, | |
| 4 | VIII | 109 | from r^3 vs V plots, | |
| 3 | IX | — | 128,7 |
Modalità di decadimento degli isotopi (50)
| Isotopo | Modalità | Intensità |
|---|---|---|
| 231 | B+ | — |
| 231 | A | — |
| 232 | B+ | — |
| 232 | A | — |
| 233 | A | 20% |
| 233 | B+ | 80% |
| 234 | B+ | 71% |
| 234 | A | 27% |
| 234 | SF | 2% |
| 235 | B+ | — |
Dati aggiuntivi
Estimated Crustal Abundance
The estimated element abundance in the earth's crust.
Not Applicable
Riferimenti (1)
Estimated Oceanic Abundance
The estimated element abundance in the earth's oceans.
Not Applicable
Riferimenti (1)
Riferimenti
(9)
Data deposited in or computed by PubChem
The half-life and atomic mass data was provided by the Atomic Mass Data Center at the International Atomic Energy Agency.
Element data are cited from the Atomic weights of the elements (an IUPAC Technical Report). The IUPAC periodic table of elements can be found at https://iupac.org/what-we-do/periodic-table-of-elements/. Additional information can be found within IUPAC publication doi:10.1515/pac-2015-0703 Copyright © 2020 International Union of Pure and Applied Chemistry.
The information are cited from Pure Appl. Chem. 2018; 90(12): 1833-2092, https://doi.org/10.1515/pac-2015-0703.
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The periodic table at the LANL (Los Alamos National Laboratory) contains basic element information together with the history, source, properties, use, handling and more. The provenance data may be found from the link under the source name.
The periodic table contains NIST's critically-evaluated data on atomic properties of the elements. The provenance data that include data for atomic spectroscopy, X-ray and gamma ray, radiation dosimetry, nuclear physics, and condensed matter physics may be found from the link under the source name. Ref: https://www.nist.gov/pml/atomic-spectra-database
This section provides all form of data related to element Curium.
The element property data was retrieved from publications.