Mendelevium (Md)
actinideSolid
標準原子量
[258]電子配置
[Rn] 7s2 5f13融点
826.85 °C沸点
データなし密度
1.03e+4 kg/m³酸化数
+2, +3電気陰性度（Pauling）
1.3第1イオン化エネルギー
6.58 eV発見年
1955原子半径
データなし詳細
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.
画像
性質
物理的性質
- ファンデルワールス半径
- 246 pm 全元素のファンデルワールス半径を比較 →
- 密度
- 1.03 × 104 kg/m³ 全元素の密度を比較 →
- 標準温度・圧力（STP）での相
- 固体 全元素の標準温度・圧力（STP）での相を比較 →
- 融点
- 826.85 °C 全元素の融点を比較 →
化学的性質
- 電気陰性度（Pauling）
- 1.3 全元素の電気陰性度（Pauling）を比較 →
- 電子親和力
- 0.997 eV
- 第1イオン化エネルギー
- 6.58 eV 全元素の第1イオン化エネルギーを比較 →
- 第2イオン化エネルギー
- 12.400043 eV 全元素の第2イオン化エネルギーを比較 →
- 第3イオン化エネルギー
- 24.300084 eV 全元素の第3イオン化エネルギーを比較 →
- 第4イオン化エネルギー
- 40.000138 eV 全元素の第4イオン化エネルギーを比較 →
- 第5イオン化エネルギー
- 54.100186 eV 全元素の第5イオン化エネルギーを比較 →
- 酸化数
- +2, +3 全元素の酸化数を比較 →
- 価電子
- 3 全元素の価電子を比較 →
- 電子配置
- [Rn] 7s2 5f13
熱力学的性質
- 昇華熱
- 4.197544 eV
- 原子化熱
- 4.197544 eV
原子核
- 陽子数
- 101 全元素の陽子数を比較 →
- 中性子数
- 157 全元素の中性子数を比較 →
- 既知の同位体
- 19 全元素の既知の同位体を比較 →
- 安定同位体
- 0 全元素の安定同位体を比較 →
- 質量数（最も安定な同位体）
- 258
- 最も安定な同位体
- Md-258
- 発見年
- 1955
存在度
データなし
結晶構造
データなし
電子構造
- 各電子殻の電子数
- 2, 8, 18, 32, 31, 8, 2 全元素の各電子殻の電子数を比較 →
識別子
- CAS登録番号
- 7440-11-1 全元素のCAS登録番号を比較 →
- 項記号
- 2F°7/2
- InChI
- InChI=1S/Md
- InChI Key
- MQVSLOYRCXQRPM-UHFFFAOYSA-N
電子配置 測定値
Md: 5f¹³ 7s²[Rn] 5f¹³ 7s²1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f¹⁴ 5d¹⁰ 6s² 6p⁶ 5f¹³ 7s²原子モデル
同位体によって中性子数、質量、安定性は変わりますが、中性原子の電子配置は変わりません。
模式的な原子モデルです。実際の縮尺とは異なります。
原子の指紋
発光／吸収スペクトル
同位体分布
安定同位体はありません。
| 質量数 | 原子質量（u） | 天然存在比 | 半減期 |
|---|---|---|---|
| 256 放射性 | 256.09389 ± 0.00013 | データなし | 77.7 分 |
| 250 放射性 | 250.08441 ± 0.00032 | データなし | 54 秒 |
| 258 放射性 | 258.0984315 ± 0.000005 | データなし | 51.59 日 |
| 261 放射性 | 261.10583 ± 0.00062 | データなし | 40 分 |
| 260 放射性 | 260.10365 ± 0.00034 | データなし | 27.8 日 |
相／状態
理由: 昇華点（826.85 °C）より801.9 °C低い
模式図、実際の縮尺とは異なります
相転移点
相転移エネルギー
昇華点で1 molを昇華させるのに必要なエネルギー
密度
標準条件下
標準条件下
原子スペクトル
全101件中10件を表示しています。 イオンの電荷の昇順で並べています。
準位データの収録状況 ?
| イオン | 電荷 | 準位 |
|---|---|---|
| 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 |
結晶構造のデータはありません
イオン半径
| 電荷 | 配位 | スピン | 半径 |
|---|---|---|---|
| +3 | 9 | データなし | 109.5 pm |
化合物
同位体 (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.
| 質量数 | 原子質量（u） | 天然存在比 | 半減期 | 崩壊形式 | |
|---|---|---|---|---|---|
| 256 放射性 | 256.09389 ± 0.00013 | データなし | 77.7 分 | β+ =90.8±0.7%α =9.2±0.7%SF<3% | |
| 250 放射性 | 250.08441 ± 0.00032 | データなし | 54 秒 | β+ =93.0±0.8%α =7.0±0.8%β+SF =0.026±1.5% | |
| 258 放射性 | 258.0984315 ± 0.000005 | データなし | 51.59 日 | α ≈100%β+<0.0015% β-<0.0015% | |
| 261 放射性 | 261.10583 ± 0.00062 | データなし | 40 分 | α ? | |
| 260 放射性 | 260.10365 ± 0.00034 | データなし | 27.8 日 | SF ≈100%α<5% ε<5% |
詳細な性質
共有結合半径（詳細）
- 共有結合半径（Pyykkö）
- 173 pm
- 共有結合半径（Pyykkö、二重結合）
- 139 pm
ファンデルワールス半径
- UFF
- 327.4 pm
番号付けの尺度
- Mendeleev
- 38
- Pettifor
- 36
- Glawe
- 45
電気陰性度の尺度
- Ghosh
- 0
分極率と分散
- 双極子分極率
- 109 a.u.
- 双極子分極率（不確かさ）
- 20 a.u.
相転移と同素体
| 融点 | 1100.15 K |
酸化数の分類
専門参考データ
結晶半径の詳細 (1)
| 電荷 | CN | スピン | rcrystal (pm) | 由来 |
|---|---|---|---|---|
| 3 | IX | — | 123.5 |
同位体の崩壊形式 (45)
| 同位体 | モード | 強度 |
|---|---|---|
| 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% |
追加データ
Estimated Crustal Abundance
The estimated element abundance in the earth's crust.
Not Applicable
参考文献 (1)
- [5] Mendelevium https://education.jlab.org/itselemental/ele101.html
Estimated Oceanic Abundance
The estimated element abundance in the earth's oceans.
Not Applicable
参考文献 (1)
- [5] Mendelevium https://education.jlab.org/itselemental/ele101.html
参考文献
(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.