Mendelevium (Md)
actinideSolid
Standard Atomic Weight
[258]Electron configuration
[Rn] 7s2 5f13Melting point
826.85 °CBoiling point
N/ADensity
1.03e+4 kg/m³Oxidation states
+2, +3Electronegativity (Pauling)
1.3Ionization energy (1st)
6.58 eVDiscovery year
1955Atomic radius
N/ADetails
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.
Images
Properties
Physical
- Van der Waals radius
- 246 pm Compare Van der Waals radius of all elements →
- Density
- 1.03 × 104 kg/m³ Compare Density of all elements →
- Phase at STP
- Solid Compare Phase at STP of all elements →
- Melting point
- 826.85 °C Compare Melting point of all elements →
Chemical
- Electronegativity (Pauling)
- 1.3 Compare Electronegativity (Pauling) of all elements →
- Electron affinity
- 0.997 eV
- Ionization energy (1st)
- 6.58 eV Compare Ionization energy (1st) of all elements →
- Ionization energy (2nd)
- 12.400043 eV Compare Ionization energy (2nd) of all elements →
- Ionization energy (3rd)
- 24.300084 eV Compare Ionization energy (3rd) of all elements →
- Ionization energy (4th)
- 40.000138 eV Compare Ionization energy (4th) of all elements →
- Ionization energy (5th)
- 54.100186 eV Compare Ionization energy (5th) of all elements →
- Oxidation states
- +2, +3 Compare Oxidation states of all elements →
- Valence electrons
- 3 Compare Valence electrons of all elements →
- Electron configuration
- [Rn] 7s2 5f13
Thermodynamic
- Heat of sublimation
- 4.197544 eV
- Heat of atomization
- 4.197544 eV
Nuclear
- Protons
- 101 Compare Protons of all elements →
- Neutrons
- 157 Compare Neutrons of all elements →
- Known isotopes
- 19 Compare Known isotopes of all elements →
- Stable isotopes
- 0 Compare Stable isotopes of all elements →
- Mass number (most stable)
- 258
- Most stable isotope
- Md-258
- Discovery year
- 1955
Abundance
N/A
Crystal Structure
N/A
Electronic Structure
- Electrons per shell
- 2, 8, 18, 32, 31, 8, 2 Compare Electrons per shell of all elements →
Identifiers
- CAS number
- 7440-11-1 Compare CAS number of all elements →
- Term symbol
- 2F°7/2
- InChI
- InChI=1S/Md
- InChI Key
- MQVSLOYRCXQRPM-UHFFFAOYSA-N
Electron Configuration Measured
Md: 5f¹³ 7s²[Rn] 5f¹³ 7s²1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f¹⁴ 5d¹⁰ 6s² 6p⁶ 5f¹³ 7s²Atomic model
Isotopes change neutron count, mass, and stability — not the electron configuration of a neutral atom.
Schematic atomic model, not to scale.
Atomic Fingerprint
Emission / Absorption Spectrum
Isotope Distribution
No stable isotopes.
| Mass number | Atomic mass (u) | Natural abundance | Half-life |
|---|---|---|---|
| 256 Radioactive | 256.09389 ± 0.00013 | N/A | 77.7 minutes |
| 250 Radioactive | 250.08441 ± 0.00032 | N/A | 54 seconds |
| 258 Radioactive | 258.0984315 ± 0.000005 | N/A | 51.59 days |
| 261 Radioactive | 261.10583 ± 0.00062 | N/A | 40 minutes |
| 260 Radioactive | 260.10365 ± 0.00034 | N/A | 27.8 days |
Phase / State
Reason: 801.9 °C below sublimation point (826.85 °C)
Schematic, not to scale
Phase transition points
Transition energies
Energy required to sublime 1 mol at sublimation point
Density
At standard conditions
At standard conditions
Atomic Spectra
Showing 10 of 101. Sorted by ion charge (ascending).
Levels Holdings ?
| Ion | Charge | Levels |
|---|---|---|
| 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 |
Crystal structure data not available
Ionic Radii
| Charge | Coordination | Spin | Radius |
|---|---|---|---|
| +3 | 9 | N/A | 109.5 pm |
Compounds
Isotopes (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.
| Mass number | Atomic mass (u) | Natural abundance | Half-life | Decay mode | |
|---|---|---|---|---|---|
| 256 Radioactive | 256.09389 ± 0.00013 | N/A | 77.7 minutes | β+ =90.8±0.7%α =9.2±0.7%SF<3% | |
| 250 Radioactive | 250.08441 ± 0.00032 | N/A | 54 seconds | β+ =93.0±0.8%α =7.0±0.8%β+SF =0.026±1.5% | |
| 258 Radioactive | 258.0984315 ± 0.000005 | N/A | 51.59 days | α ≈100%β+<0.0015% β-<0.0015% | |
| 261 Radioactive | 261.10583 ± 0.00062 | N/A | 40 minutes | α ? | |
| 260 Radioactive | 260.10365 ± 0.00034 | N/A | 27.8 days | SF ≈100%α<5% ε<5% |
Extended Properties
Covalent Radii (Extended)
- Covalent radius (Pyykkö)
- 173 pm
- Covalent radius (Pyykkö, double)
- 139 pm
Van der Waals Radii
- UFF
- 327.4 pm
Numbering Scales
- Mendeleev
- 38
- Pettifor
- 36
- Glawe
- 45
Electronegativity Scales
- Ghosh
- 0
Polarizability & Dispersion
- Dipole polarizability
- 109 a.u.
- Dipole polarizability (unc.)
- 20 a.u.
Phase Transitions & Allotropes
| Melting point | 1100.15 K |
Oxidation State Categories
Advanced Reference Data
Crystal Radii Detail (1)
| Charge | CN | Spin | rcrystal (pm) | Origin |
|---|---|---|---|---|
| 3 | IX | — | 123.5 |
Isotope Decay Modes (45)
| Isotope | Mode | Intensity |
|---|---|---|
| 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% |
Additional Data
Estimated Crustal Abundance
The estimated element abundance in the earth's crust.
Not Applicable
References (1)
- [5] Mendelevium https://education.jlab.org/itselemental/ele101.html
Estimated Oceanic Abundance
The estimated element abundance in the earth's oceans.
Not Applicable
References (1)
- [5] Mendelevium https://education.jlab.org/itselemental/ele101.html
References
(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.