Neptunium (Np)
actinideSolid
Peso atómico estándar
[237]Configuración electrónica
[Rn] 7s2 5f4 6d1Punto de fusión
643,85 °CPunto de ebullición
3901,85 °CDensidad
2,025e+4 kg/m³Estados de oxidación
+2, +3, +4, +5, +6, +7Electronegatividad (Pauling)
1,36Energía de ionización (1.ª)
6,265608 eVAño de descubrimiento
1940Radio atómico
175 pmDetalles
Neptunium is a radioactive actinide and the first transuranium element. It is produced mainly by neutron reactions involving uranium in nuclear reactors and occurs naturally only in minute amounts from neutron capture and decay processes in uranium ores. Its chemistry bridges uranium and plutonium, with several accessible oxidation states in solution. The isotope ²³⁷Np is the most important for handling and study because of its long half-life and availability as a reactor by-product.
Neptunium metal buttons (photo courtesy Lawrence Berkeley National Laboratory)
Neptunium was first produced by Edwin M. McMillian and Philip H. Abelson, working at the University of California, Berkeley, in 1940. They produced neptunium-239, an isotope of neptunium with a half-life of about 2.4 days, by bombarding uranium with slow moving neutrons.
Named for the planet Neptune (named after the Roman god of the sea), the next planet out from the Sun after Uranus. There were many early false reports of the discovery of neptunium. The most significant was by Enrico Fermi who believed that bombarding uranium with neutrons followed by beta decay would lead to the formation of element 93. In 1934, he bombarded uranium atoms with neutrons and reported that he had produced elements 93 and 94. As it turned out, Fermi had actually fissioned or split uranium atoms into many fragment radioisotopes. The explanation and announcement of the discovery of fission was later published by Hahn and Strassman, although it was their co-worker Lisa Meitner who had correctly interpreted the results of the experiments. In 1940, with excitement about fission reaching the University of California at Berkeley, Professor Edwin McMillan and graduate student Philip Abelson bombarded uranium with cyclotron-produced moderated (slow) neutrons, resulting not in “fission” but "fusion" of the reactants forming the new element 93, which they named "neptunium":
23892U + 10n → 23992U → 23993Np + β-
Neptunium-239 was the first transuranium element produced synthetically and the first actinide series transuranium element discovered. This isotope has a beta-decay half-life of 2.3565 days, which forms daughter product plutonium-239 with a half-life of 24,000 years.
Metallic neptunium has been prepared in visible quantities. Fresh metal is silvery, dense, and chemically reactive, but it tarnishes in air as oxide layers form. It has several solid allotropes, and bulk physical measurements are limited by radioactivity, scarcity, and self-heating.
Neptunium has no broad commercial use as an element. ²³⁷Np is used in research on actinide chemistry, nuclear fuel cycles, and long-lived radioactive waste behavior. It is also the principal target material for producing ²³⁸Pu by neutron irradiation; ²³⁸Pu is then used in radioisotope heat sources and power systems. Small quantities of neptunium compounds have been used as analytical standards and in radiochemical method development.
Neptunium's most stable isotope, neptunium-237, has a half-life of about 2,144,000 years. It decays into protactinium-233 through alpha decay. Neptunium-237, which is produced in gram quantities as a by-product of the production of plutonium in nuclear reactors, is used in neutron detectors.
Once considered to be completely artificial, extremely small amounts of neptunium are produced naturally in uranium ores through the interaction of atoms of uranium in the ore with neutrons produced by the decay of other atoms of uranium in the ore.
Isotopes in Industry
237Np (with a half-life of 2.14×106 years) is fissionable, meaning that neptunium can be bombarded with neutrons and, as a result, create more neutrons that are free to interact with nearby material and can be used in fast neutron reactors or in nuclear weapons (Fig. IUPAC.93.1) [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., [603] P. Weiss. Science News.162, 259 (2002)., [604] T. Kenna. J. Anal. At. Spectrom.17, 1471 (2002).. 237Np is used in neutron detection instruments [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..
Isotopes Used as a Source of Radioactive Isotope(s)
237Np is used in the production of 238Pu (with a half-life of 87.7 years), which is an emitter of alpha particles used in thermoelectric generators and radioisotope-heater units. When 237Np captures a neutron, it becomes 238Np, with a half-life of 2.117 days, which decays to 238Pu [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..
Neptunium forms compounds in oxidation states from +3 to +7, with +4, +5, and +6 especially important in aqueous chemistry. The neptunyl ion NpO₂⁺ is a characteristic +5 species and is often relatively mobile in oxidizing waters, while NpO₂²⁺ represents +6 chemistry. Neptunium dioxide NpO₂ is a stable refractory oxide and an important solid phase. Halides such as neptunium tetrachloride NpCl₄ and neptunium hexafluoride NpF₆ illustrate the element’s actinide-like coordination and redox behavior.
See more information at the Neptunium compound page.
All neptunium isotopes are radioactive, and hazards depend strongly on isotope, chemical form, and exposure route. ²³⁷Np emits mainly alpha radiation with associated gamma emissions from decay products, so ingestion, inhalation, or contamination of wounds is the principal concern. Finely divided metal and soluble compounds require strict radiological containment. External dose rates can be significant for some samples because of accompanying gamma-emitting impurities or daughters.
Natural neptunium is extremely scarce, but anthropogenic neptunium occurs in spent nuclear fuel, reprocessing wastes, and fallout residues. Environmental behavior is controlled by oxidation state, complexation, mineral sorption, and reducing conditions. Np(V) as NpO₂⁺ can migrate more readily than many tetravalent actinides, whereas Np(IV) tends to form less soluble solids or strongly sorbed species. Its long half-life makes it important in repository performance assessments.
Neptunium is not traded as a commodity and has no ordinary industrial supply chain. Recoverable ²³⁷Np is generated as a by-product in irradiated uranium fuel and can be separated only in specialized nuclear facilities under heavy regulation. Demand is small and centered on research inventories and on target preparation for ²³⁸Pu production. Costs are dominated by radiochemical separation, safeguards, licensing, waste management, and secure storage rather than by ore mining or conventional refining.
Produced by bombarding uranium with slow neutrons.
Neptunium has no stable isotopes, so any primordial neptunium has decayed away. It can be formed in trace amounts by neutron capture in uranium-bearing materials and in nuclear explosions or reactors, and transient neptunium isotopes may occur in astrophysical rapid neutron-capture processes. Its extraterrestrial abundance is effectively negligible compared with long-lived actinides such as uranium and thorium.
- Neptunium was named after Neptune, following uranium’s naming after Uranus.
- ²³⁷Np has a half-life of about 2.14 million years.
- Neptunium was the first element beyond uranium to be identified.
- NpF₆ is volatile, a property relevant to actinide fluoride chemistry.
- The common aqueous Np(V) ion is linear neptunyl, NpO₂⁺.
- Separated neptunium metal darkens on exposure to air.
Imágenes
Propiedades
Físicas
- Radio atómico (empírico)
- 175 pm Comparar Radio atómico (empírico) de todos los elementos →
- Radio covalente
- 190 pm Comparar Radio covalente de todos los elementos →
- Radio de van der Waals
- 221 pm Comparar Radio de van der Waals de todos los elementos →
- Densidad
- 2,025 × 104 kg/m³ Comparar Densidad de todos los elementos →
- Volumen molar
- 0,0211 L/mol
- Fase en CNPT
- Sólido Comparar Fase en CNPT de todos los elementos →
- Punto de fusión
- 643,85 °C Comparar Punto de fusión de todos los elementos →
- Punto de ebullición
- 3901,85 °C Comparar Punto de ebullición de todos los elementos →
- Estructura cristalina
- Ortorrómbica Comparar Estructura cristalina de todos los elementos →
Químicas
- Electronegatividad (Pauling)
- 1,36 Comparar Electronegatividad (Pauling) de todos los elementos →
- Afinidad electrónica
- 0,48 eV
- Energía de ionización (1.ª)
- 6,265608 eV Comparar Energía de ionización (1.ª) de todos los elementos →
- Energía de ionización (2.ª)
- 11,50004 eV Comparar Energía de ionización (2.ª) de todos los elementos →
- Energía de ionización (3.ª)
- 19,700068 eV Comparar Energía de ionización (3.ª) de todos los elementos →
- Energía de ionización (4.ª)
- 33,800116 eV Comparar Energía de ionización (4.ª) de todos los elementos →
- Energía de ionización (5.ª)
- 48,000165 eV Comparar Energía de ionización (5.ª) de todos los elementos →
- Estados de oxidación
- +2, +3, +4, +5, +6, +7 Comparar Estados de oxidación de todos los elementos →
- Electrones de valencia
- 3 Comparar Electrones de valencia de todos los elementos →
- Configuración electrónica
- [Rn] 7s2 5f4 6d1
Termodinámicas
- Calor de fusión
- 0,10364305 eV Comparar Calor de fusión de todos los elementos →
- Calor de vaporización
- 3,482407 eV Comparar Calor de vaporización de todos los elementos →
- Calor de sublimación
- 4,33228 eV
- Calor de atomización
- 4,33228 eV
- Entalpía de atomización
- 4,817329 eV
Nucleares
- Protones
- 93 Comparar Protones de todos los elementos →
- Neutrones
- 144 Comparar Neutrones de todos los elementos →
- Isótopos conocidos
- 27 Comparar Isótopos conocidos de todos los elementos →
- Isótopos estables
- 0 Comparar Isótopos estables de todos los elementos →
- Número másico (isótopo más estable)
- 237
- Isótopo más estable
- Np-237
- Año de descubrimiento
- 1940
Abundancia
N/D
Estructura cristalina
- Constante de red a
- 472 pm
Estructura electrónica
- Electrones por capa
- 2, 8, 18, 32, 22, 9, 2 Comparar Electrones por capa de todos los elementos →
Identificadores
- Número CAS
- 7439-99-8 Comparar Número CAS de todos los elementos →
- Símbolo del término
- 6L11/2
- InChI
- InChI=1S/Np
- Clave InChI
- LFNLGNPSGWYGGD-UHFFFAOYSA-N
Configuración electrónica Medido
Np: 5f⁴ 6d¹ 7s²[Rn] 5f⁴ 6d¹ 7s²1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f¹⁴ 5d¹⁰ 6s² 6p⁶ 5f⁴ 6d¹ 7s²Modelo atómico
Los isótopos cambian el número de neutrones, la masa y la estabilidad, pero no la configuración electrónica de un átomo neutro.
Modelo atómico esquemático, no a escala.
Huella atómica
Espectro de emisión / absorción
Distribución isotópica
No hay isótopos estables.
| Número másico | Masa atómica (u) | Abundancia natural | Periodo de semidesintegración |
|---|---|---|---|
| 219 Radiactivo | 219,03143 ± 0,00021 | N/D | 570 us |
| 227 Radiactivo | 227,034957 ± 0,000078 | N/D | 510 ms |
| 222 Radiactivo | 222,0333 ± 0,00021 | N/D | 480 ns |
| 235 Radiactivo | 235,0440635 ± 0,0000021 | N/D | 396.1 días |
| 236 Radiactivo | 236,04657 ± 0,000054 | N/D | 153 ky |
Fase / Estado
Motivo: 618,9 °C por debajo del punto de fusión (643,85 °C)
Esquemático, no a escala
Puntos de transición de fase
Energías de transición
Energía necesaria para fundir 1 mol en el punto de fusión
Energía necesaria para vaporizar 1 mol en el punto de ebullición
Energía necesaria para sublimar 1 mol en el punto de sublimación
Densidad
En condiciones estándar
En condiciones estándar
Espectros atómicos
Se muestran 10 de 93. Ordenado por carga del ion (ascendente).
Líneas disponibles ?
| Ion | Carga | Total de líneas | Probabilidades de transición | Designaciones de los niveles |
|---|---|---|---|---|
| Np I | 0 | 96 | 0 | 0 |
Niveles disponibles ?
| Ion | Carga | Niveles |
|---|---|---|
| Np I | 0 | 2 |
| Np II | +1 | 2 |
| Np III | +2 | 2 |
| Np IV | +3 | 2 |
| Np V | +4 | 2 |
| Np VI | +5 | 2 |
| Np VII | +6 | 2 |
| Np VIII | +7 | 2 |
| Np IX | +8 | 2 |
| Np X | +9 | 2 |
Radios iónicos
| Carga | Coordinación | Espín | Radio |
|---|---|---|---|
| +2 | 6 | N/D | 110.00000000000001 pm |
| +3 | 6 | N/D | 101 pm |
| +3 | 9 | N/D | 117.8 pm |
| +4 | 6 | N/D | 87 pm |
| +4 | 8 | N/D | 98 pm |
| +5 | 6 | N/D | 75 pm |
| +6 | 6 | N/D | 72 pm |
| +7 | 6 | N/D | 71 pm |
Compuestos
Isótopos (5)
There are 25 known radioactive isotopes of neptunium ranging in atomic weights from 225 to 244 with 5 of those as metastable isotopes. The most stable are Np-237 with a half-life of 2.14 million years; Np-236 with a half-life of 154,000 years; and Np-235 with a half-life of 396 days. All of the remaining isotopes have half-lives less than 4.5 days, with most less than 50 minutes. The primary decay mode for isotopes lighter than 237Np is by electron capture with a great deal of alpha emission. The products are mostly isotopes of uranium. The primary decay mode for Np-237 is by alpha-decay forming protactinium. The primary decay mode for the isotopes heavier than Np-237 is by beta-decay, forming plutonium. Neptunium-237, after decaying to protactinium then to uranium, eventually decays to form bismuth-209 and thallium-205. Unlike most other common heavy nuclei which decay to make isotopes of lead this decay chain is known as the neptunium series.
| Número másico | Masa atómica (u) | Abundancia natural | Periodo de semidesintegración | Modo de desintegración | |
|---|---|---|---|---|---|
| 219 Radiactivo | 219,03143 ± 0,00021 | N/D | 570 us | α =100% | |
| 227 Radiactivo | 227,034957 ± 0,000078 | N/D | 510 ms | α ≈100%β+ ? | |
| 222 Radiactivo | 222,0333 ± 0,00021 | N/D | 480 ns | α =100% | |
| 235 Radiactivo | 235,0440635 ± 0,0000021 | N/D | 396.1 días | ε =99.99740±1.3%α =0.00260±1.3% | |
| 236 Radiactivo | 236,04657 ± 0,000054 | N/D | 153 ky | ε =86.3±0.8%β- =13.5±0.8%α =0.16±0.4% |
Propiedades ampliadas
Radios covalentes (ampliados)
- Radio covalente (Pyykkö)
- 171 pm
- Radio covalente (Pyykkö, enlace doble)
- 136 pm
- Radio covalente (Pyykkö, enlace triple)
- 116 pm
Radios de van der Waals
- Alvarez
- 282 pm
- UFF
- 342,4 pm
- MM3
- 252 pm
Radios atómicos y metálicos
- Radio atómico (Rahm)
- 281 pm
Escalas de numeración
- Mendeleev
- 22
- Pettifor
- 44
- Glawe
- 37
Escalas de electronegatividad
- Ghosh
- 0
Polarizabilidad y dispersión
- Polarizabilidad dipolar
- 151 a.u.
- Polarizabilidad dipolar (incert.)
- 20 a.u.
Transiciones de fase y alótropos
| Punto de fusión | 917,15 K |
Categorías de estados de oxidación
Datos de referencia avanzados
Detalle de los radios cristalinos (8)
| Carga | CN | Espín | rcrystal (pm) | Origen |
|---|---|---|---|---|
| 2 | VI | 124 | ||
| 3 | VI | 115 | from r^3 vs V plots, | |
| 4 | VI | 101 | from r^3 vs V plots, | |
| 4 | VIII | 112 | from r^3 vs V plots, | |
| 5 | VI | 89 | ||
| 6 | VI | 86 | from r^3 vs V plots, | |
| 7 | VI | 85 | Ahrens (1952) ionic radius, | |
| 3 | IX | — | 131,8 |
Modos de desintegración de los isótopos (44)
| Isótopo | Modo | Intensidad |
|---|---|---|
| 219 | A | 100% |
| 220 | A | 100% |
| 221 | A | — |
| 222 | A | 100% |
| 223 | A | 100% |
| 224 | A | 100% |
| 225 | A | 100% |
| 225 | B+ | — |
| 226 | A | 100% |
| 226 | B+ | — |
Datos adicionales
Estimated Crustal Abundance
The estimated element abundance in the earth's crust.
Not Applicable
Referencias (1)
- [5] Neptunium https://education.jlab.org/itselemental/ele093.html
Estimated Oceanic Abundance
The estimated element abundance in the earth's oceans.
Not Applicable
Referencias (1)
- [5] Neptunium https://education.jlab.org/itselemental/ele093.html
Referencias
(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 Neptunium.
The element property data was retrieved from publications.