Mendelevium (Md)
actinideSolid
Peso atômico padrão
[258]Configuração eletrônica
[Rn] 7s2 5f13Ponto de fusão
826,85 °CPonto de ebulição
N/DDensidade
1,03e+4 kg/m³Estados de oxidação
+2, +3Eletronegatividade (Pauling)
1,3Energia de ionização (1ª)
6,58 eVAno da descoberta
1955Raio atômico
N/DDetalhes
Mendelevium is a synthetic actinide and the first element that was initially identified one atom at a time. All known isotopes are radioactive, and none is present in nature in measurable primordial amounts. Its chemistry is dominated by the +3 oxidation state, broadly resembling neighboring late actinides and lanthanides, with a distinctive accessible +2 state under reducing conditions. Work on mendelevium is limited by very small samples and short half-lives.
Mendelevium does not occur naturally in the Earth’s crust. It was first synthesized in 1955 by Glenn T. Seaborg and his team at the University of California using the reactions 253Es (4He, n) 256Md and 253Es (4He, 2n) 255Md. Mendelevium is named for the Russian scientist, Dmitri Mendeleev (Fig. IUPAC.101.1), who developed the Periodic Table of the chemical elements [636], [637]. There are no applications for isotopes of mendelevium aside from scientific research.
Experiments seem to show that the element possesses a moderately stable dipositive (II) oxidation state in addition to the tripositive (III) oxidation state, which is characteristic of the actinide elements.
Mendelevium was first produced by Stanley G. Thompson, Glenn T. Seaborg, Bernard G. Harvey, Gregory R. Choppin and Albert Ghiorso working at the University of California, Berkeley, in 1955. They bombarded atoms of einsteinium-253 with helium ions using a device known as a cyclotron. This produced atoms of mendelevium-256, an isotope with a half-life of about 77 minutes, and a free neutron. Mendelevium's most stable isotope, mendelevium-258, has a half-life of about 51.5 days. It decays into einsteinium-254 through alpha decay or decays through spontaneous fission.
Mendelevium is named after Dmitri Mendeleev. It is the ninth transuranium element of the actinide series discovered. It was first identified by Ghiorso, Harvey, Choppin, Thompson, and Seaborg in early in 1955 during the bombardment of the isotope 253Es with helium ions in the Berkeley 60-inch cyclotron. The isotope produced was 256Md, which has a half-life of 76 min. This first identification was notable in that 256Md was synthesized on a one-atom-at-a-time basis.
No macroscopic sample of mendelevium has been isolated, so its real bulk appearance is unknown. A metallic solid is expected by periodic trends, but color, texture, density, and other ordinary bulk properties have not been directly measured.
Mendelevium has no practical use outside scientific research. Its isotopes are produced for nuclear-chemistry studies, tracer-scale separation experiments, and investigations of actinide electronic structure and redox behavior. Historically, mendelevium was important in demonstrating that new elements could be discovered and chemically characterized from only a few atoms. It is not used in medicine, industry, consumer products, or power generation.
Since only small amounts of mendelevium have ever been produced, it currently has no uses outside of basic scientific research.
256Md has been used to elucidate some of the chemical properties of mendelevium in aqueous solution.
Mendelevium chemistry has been studied in solution and on surfaces at tracer scale. The Md³⁺ ion is the most stable aqueous form and behaves much like a heavy trivalent actinide. The Md²⁺ ion can be produced by reduction and is unusually important for identifying mendelevium relative to many neighboring actinides. Simple compounds such as mendelevium(III) chloride, MdCl₃, and mendelevium(III) fluoride, MdF₃, are inferred or studied only in minute quantities; no bulk compound chemistry exists.
See more information at the Mendelevium compound page.
The main hazard from mendelevium is ionizing radiation, with risk depending strongly on isotope, activity, chemical form, and containment. The longest-lived isotope, ²⁵⁸Md, has a half-life of about 51 days, while many others decay much faster. Amounts normally handled are extremely small, but work requires specialized radiochemical facilities to prevent contamination and external or internal exposure.
Mendelevium has no significant natural environmental cycle. Any environmental presence would come from specialized nuclear research or decay chains in artificial material and would involve vanishingly small quantities. Because it is radioactive and produced atom by atom or in tracer amounts, its environmental chemistry is inferred mainly from actinide behavior rather than observed field distribution.
Mendelevium is not a traded commodity and has no commercial supply chain. It is made in high-flux reactors or particle accelerators by neutron capture and charged-particle nuclear reactions involving heavy actinide targets, followed by rapid radiochemical separation. Production yields are extremely small, often atom-scale to tracer-scale, and are constrained by target availability, irradiation time, isotope half-life, and the need for specialized laboratories. There is no meaningful recycling market or industrial substitution issue because demand is confined to research.
Made by bombarding einsteinium with helium ions.
Mendelevium is not expected to have appreciable cosmic abundance. Its isotopes have half-lives far too short to survive since stellar nucleosynthesis or Solar System formation. It may be formed transiently in extreme neutron-rich events or in artificial nuclear reactions, but any naturally produced atoms would decay quickly and would not accumulate in planets, meteorites, or interstellar matter.
- Mendelevium was named for Dmitri Mendeleev, the developer of the periodic table.
- The first identification used only about a few atoms produced by bombarding einsteinium.
- Its accessible +2 state is a key diagnostic feature in radiochemical separations.
- ²⁵⁶Md has been used in atom-at-a-time chemical studies despite its short half-life.
- No weighing, casting, or visual inspection of elemental mendelevium has been possible.
Imagens
Propriedades
Física
- Raio de van der Waals
- 246 pm Comparar Raio de van der Waals de todos os elementos →
- Densidade
- 1,03 × 104 kg/m³ Comparar Densidade de todos os elementos →
- Fase nas CNTP
- Sólido Comparar Fase nas CNTP de todos os elementos →
- Ponto de fusão
- 826,85 °C Comparar Ponto de fusão de todos os elementos →
Química
- Eletronegatividade (Pauling)
- 1,3 Comparar Eletronegatividade (Pauling) de todos os elementos →
- Afinidade eletrônica
- 0,997 eV
- Energia de ionização (1ª)
- 6,58 eV Comparar Energia de ionização (1ª) de todos os elementos →
- Energia de ionização (2ª)
- 12,400043 eV Comparar Energia de ionização (2ª) de todos os elementos →
- Energia de ionização (3ª)
- 24,300084 eV Comparar Energia de ionização (3ª) de todos os elementos →
- Energia de ionização (4ª)
- 40,000138 eV Comparar Energia de ionização (4ª) de todos os elementos →
- Energia de ionização (5ª)
- 54,100186 eV Comparar Energia de ionização (5ª) de todos os elementos →
- Estados de oxidação
- +2, +3 Comparar Estados de oxidação de todos os elementos →
- Elétrons de valência
- 3 Comparar Elétrons de valência de todos os elementos →
- Configuração eletrônica
- [Rn] 7s2 5f13
Termodinâmica
- Calor de sublimação
- 4,197544 eV
- Calor de atomização
- 4,197544 eV
Nuclear
- Prótons
- 101 Comparar Prótons de todos os elementos →
- Nêutrons
- 157 Comparar Nêutrons de todos os elementos →
- Isótopos conhecidos
- 19 Comparar Isótopos conhecidos de todos os elementos →
- Isótopos estáveis
- 0 Comparar Isótopos estáveis de todos os elementos →
- Número de massa (mais estável)
- 258
- Isótopo mais estável
- Md-258
- Ano da descoberta
- 1955
Abundância
N/D
Estrutura cristalina
N/D
Estrutura eletrônica
- Elétrons por camada
- 2, 8, 18, 32, 31, 8, 2 Comparar Elétrons por camada de todos os elementos →
Identificadores
- Número CAS
- 7440-11-1 Comparar Número CAS de todos os elementos →
- Símbolo de termo
- 2F°7/2
- InChI
- InChI=1S/Md
- Chave InChI
- MQVSLOYRCXQRPM-UHFFFAOYSA-N
Configuração eletrônica Medido
Md: 5f¹³ 7s²[Rn] 5f¹³ 7s²1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f¹⁴ 5d¹⁰ 6s² 6p⁶ 5f¹³ 7s²Modelo atômico
Os isótopos alteram o número de nêutrons, a massa e a estabilidade — não a configuração eletrônica de um átomo neutro.
Modelo atômico esquemático, sem escala.
Assinatura atômica
Espectro de emissão / absorção
Distribuição isotópica
Sem isótopos estáveis.
| Número de massa | Massa atômica (u) | Abundância natural | Meia-vida |
|---|---|---|---|
| 256 Radioativo | 256,09389 ± 0,00013 | N/D | 77.7 minutos |
| 250 Radioativo | 250,08441 ± 0,00032 | N/D | 54 segundos |
| 258 Radioativo | 258,0984315 ± 0,000005 | N/D | 51.59 dias |
| 261 Radioativo | 261,10583 ± 0,00062 | N/D | 40 minutos |
| 260 Radioativo | 260,10365 ± 0,00034 | N/D | 27.8 dias |
Fase / Estado
Motivo: 801,9 °C abaixo do ponto de sublimação (826,85 °C)
Esquemático, sem escala
Pontos de transição de fase
Energias de transição
Energia necessária para sublimar 1 mol no ponto de sublimação
Densidade
Em condições padrão
Em condições padrão
Espectros atômicos
Mostrando 10 de 101. Ordenado por carga do íon (ordem crescente).
Dados de níveis disponíveis ?
| Íon | Carga | Níveis |
|---|---|---|
| Md I | 0 | 2 |
| Md II | +1 | 2 |
| Md III | +2 | 2 |
| Md IV | +3 | 2 |
| Md V | +4 | 2 |
| Md VI | +5 | 2 |
| Md VII | +6 | 2 |
| Md VIII | +7 | 2 |
| Md IX | +8 | 2 |
| Md X | +9 | 2 |
Dados de estrutura cristalina indisponíveis
Raios iônicos
| Carga | Coordenação | Spin | Raio |
|---|---|---|---|
| +3 | 9 | N/D | 109.5 pm |
Compostos
Isótopos (5)
Fourteen isotopes are now recognized. 258Md has a half-life of 2 months. This isotope has been produced by the bombardment of an isotope of einsteinium with ions of helium. Eventually enough 258Md should be made to determine its physical properties.
| Número de massa | Massa atômica (u) | Abundância natural | Meia-vida | Modo de decaimento | |
|---|---|---|---|---|---|
| 256 Radioativo | 256,09389 ± 0,00013 | N/D | 77.7 minutos | β+ =90.8±0.7%α =9.2±0.7%SF<3% | |
| 250 Radioativo | 250,08441 ± 0,00032 | N/D | 54 segundos | β+ =93.0±0.8%α =7.0±0.8%β+SF =0.026±1.5% | |
| 258 Radioativo | 258,0984315 ± 0,000005 | N/D | 51.59 dias | α ≈100%β+<0.0015% β-<0.0015% | |
| 261 Radioativo | 261,10583 ± 0,00062 | N/D | 40 minutos | α ? | |
| 260 Radioativo | 260,10365 ± 0,00034 | N/D | 27.8 dias | SF ≈100%α<5% ε<5% |
Propriedades ampliadas
Raios covalentes (dados ampliados)
- Raio covalente (Pyykkö)
- 173 pm
- Raio covalente (Pyykkö, ligação dupla)
- 139 pm
Raios de van der Waals
- UFF
- 327,4 pm
Escalas de numeração
- Mendeleev
- 38
- Pettifor
- 36
- Glawe
- 45
Escalas de eletronegatividade
- Ghosh
- 0
Polarizabilidade e dispersão
- Polarizabilidade dipolar
- 109 a.u.
- Polarizabilidade dipolar (incerteza)
- 20 a.u.
Transições de fase e alótropos
| Ponto de fusão | 1100,15 K |
Categorias de estados de oxidação
Dados de referência avançados
Detalhes dos raios cristalinos (1)
| Carga | CN | Spin | rcrystal (pm) | Origem |
|---|---|---|---|---|
| 3 | IX | — | 123,5 |
Modos de decaimento dos isótopos (45)
| Isótopo | Modo | Intensidade |
|---|---|---|
| 244 | A | 100% |
| 244 | B+ | — |
| 244 | B+SF | 14% |
| 245 | A | 100% |
| 245 | B+ | — |
| 246 | A | 100% |
| 247 | A | 100% |
| 247 | SF | 0,1% |
| 248 | B+ | 80% |
| 248 | A | 20% |
Dados adicionais
Estimated Crustal Abundance
The estimated element abundance in the earth's crust.
Not Applicable
Referências (1)
- [5] Mendelevium https://education.jlab.org/itselemental/ele101.html
Estimated Oceanic Abundance
The estimated element abundance in the earth's oceans.
Not Applicable
Referências (1)
- [5] Mendelevium https://education.jlab.org/itselemental/ele101.html
Referências
(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.
Thomas Jefferson National Accelerator Facility (Jefferson Lab) is one of 17 national laboratories funded by the U.S. Department of Energy. The lab's primary mission is to conduct basic research of the atom's nucleus using the lab's unique particle accelerator, known as the Continuous Electron Beam Accelerator Facility (CEBAF). For more information visit https://www.jlab.org/
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 Mendelevium.
The element property data was retrieved from publications.