Mendelevium is a synthetic element with chemical symbol Md (formerly Mv) and atomic number 101. A metallic radioactive transuranic element in the actinide series, it is the first element that currently cannot be produced in macroscopic quantities through neutron bombardment of lighter elements. It is the third-to-last actinide and the ninth transuranic element. It can only be produced in particle accelerators by bombarding lighter elements with charged particles. A total of sixteen mendelevium isotopes are known, the most stable being 258Md with a half-life of 51 days; nevertheless, the shorter-lived 256Md (half-life 1.17 hours) is most commonly used in chemistry because it can be produced on a larger scale.

Mendelevium was discovered by bombarding einsteinium with alpha particles in 1955, the same method still used to produce it today. It was named after Dmitri Mendeleev, father of the periodic table of the chemical elements. Using available microgram quantities of the isotope einsteinium-253, over a million mendelevium atoms may be produced each hour. The chemistry of mendelevium is typical for the late actinides, with a preponderance of the +3 oxidation state but also an accessible +2 oxidation state. Owing to the small amounts of produced mendelevium and all of its isotopes having relatively short half-lives, there are currently no uses for it outside basic scientific research.

Mendelevium,  101Md
Pronunciation/ˌmɛndɪˈliːviəm/ (MEN-də-LEE-vee-əm)
Mass number258 (most stable isotope)
Mendelevium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson


Atomic number (Z)101
Groupgroup n/a
Periodperiod 7
Element category  actinide
Electron configuration[Rn] 5f13 7s2
Electrons per shell
2, 8, 18, 32, 31, 8, 2
Physical properties
Phase at STPunknown phase (predicted)
Melting point1100 K ​(827 °C, ​1521 °F) (predicted)
Density (near r.t.)10.3(7) g/cm3 (predicted)[1]
Atomic properties
Oxidation states+2, +3
ElectronegativityPauling scale: 1.3
Ionization energies
  • 1st: 635 kJ/mol
  • (estimated)
Other properties
Natural occurrencesynthetic
Crystal structureface-centered cubic (fcc)
Face-centered cubic crystal structure for mendelevium

CAS Number7440-11-1
Namingafter Dmitri Mendeleev
DiscoveryLawrence Berkeley National Laboratory (1955)
Main isotopes of mendelevium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
257Md syn 5.52 h ε 257Fm
α 253Es
258Md syn 51.5 d ε 258Fm
260Md syn 31.8 d SF
α 256Es
ε 260Fm
β 260No


Berkeley 60-inch cyclotron
The 60-inch cyclotron at the Lawrence Radiation Laboratory, University of California, Berkeley, in August 1939

Mendelevium was the ninth transuranic element to be synthesized. It was first synthesized by Albert Ghiorso, Glenn T. Seaborg, Gregory Robert Choppin, Bernard G. Harvey, and team leader Stanley G. Thompson in early 1955 at the University of California, Berkeley. The team produced 256Md (half-life of 77 minutes[2]) when they bombarded an 253Es target consisting of only a billion (109) einsteinium atoms with alpha particles (helium nuclei) in the Berkeley Radiation Laboratory's 60-inch cyclotron, thus increasing the target's atomic number by two. 256Md thus became the first isotope of any element to be synthesized one atom at a time. In total, seventeen mendelevium atoms were produced.[3] This discovery was part of a program, begun in 1952, that irradiated plutonium with neutrons to transmute it into heavier actinides.[4] This method was necessary as the previous method used to synthesize transuranic elements, neutron capture, could not work because of a lack of known beta decaying isotopes of fermium that would produce isotopes of the next element, mendelevium, and also due to the very short half-life to spontaneous fission of 258Fm that thus constituted a hard limit to the success of the neutron capture process.[2]

External video
Reenactment of the discovery of mendelevium at Berkeley

To predict if the production of mendelevium would be possible, the team made use of a rough calculation. The number of atoms that would be produced would be approximately equal to the product of the number of atoms of target material, the target's cross section, the ion beam intensity, and the time of bombardment; this last factor was related to the half-life of the product when bombarding for a time on the order of its half-life. This gave one atom per experiment. Thus under optimum conditions, the preparation of only one atom of element 101 per experiment could be expected. This calculation demonstrated that it was feasible to go ahead with the experiment.[3] The target material, einsteinium-253, could be produced readily from irradiating plutonium: one year of irradiation would give a billion atoms, and its three-week half-life meant that the element 101 experiments could be conducted in one week after the produced einsteinium was separated and purified to make the target. However, it was necessary to upgrade the cyclotron to obtain the needed intensity of 1014 alpha particles per second; Seaborg applied for the necessary funds.[4]

Md datasheet
The data sheet, showing stylus tracing and notes, that proved the discovery of mendelevium.

While Seaborg applied for funding, Harvey worked on the einsteinium target, while Thomson and Choppin focused on methods for chemical isolation. Choppin suggested using α-hydroxyisobutyric acid to separate the mendelevium atoms from those of the lighter actinides.[4] The actual synthesis was done by a recoil technique, introduced by Albert Ghiorso. In this technique, the einsteinium was placed on the opposite side of the target from the beam, so that the recoiling mendelevium atoms would get enough momentum to leave the target and be caught on a catcher foil made of gold. This recoil target was made by an electroplating technique, developed by Alfred Chetham-Strode. This technique gave a very high yield, which was absolutely necessary when working with such a rare and valuable product as the einsteinium target material.[3] The recoil target consisted of 109 atoms of 253Es which were deposited electrolytically on a thin gold foil. It was bombarded by 41 MeV alpha particles in the Berkeley cyclotron with a very high beam density of 6×1013 particles per second over an area of 0.05 cm2. The target was cooled by water or liquid helium, and the foil could be replaced.[3][5]

Initial experiments were carried out in September 1954. No alpha decay was seen from mendelevium atoms; thus, Ghiorso suggested that the mendelevium had all decayed by electron capture to fermium and that the experiment should be repeated to search instead for spontaneous fission events.[4] The repetition of the experiment happened in February 1955.[4]

The element was named after Dmitri Mendeleev.

On the day of discovery, 19 February, alpha irradiation of the einsteinium target occurred in three three-hour sessions. The cyclotron was in the University of California campus, while the Radiation Laboratory was on the next hill. To deal with this situation, a complex procedure was used: Ghiorso took the catcher foils (there were three targets and three foils) from the cyclotron to Harvey, who would use aqua regia to dissolve it and pass it through an anion-exchange resin column to separate out the transuranium elements from the gold and other products.[4][6] The resultant drops entered a test tube, which Choppin and Ghiorso took in a car to get to the Radiation Laboratory as soon as possible. There Thompson and Choppin used a cation-exchange resin column and the α-hydroxyisobutyric acid. The solution drops were collected on platinum disks and dried under heat lamps. The three disks were expected to contain respectively the fermium, no new elements, and the mendelevium. Finally, they were placed in their own counters, which were connected to recorders such that spontaneous fission events would be recorded as huge deflections in a graph showing the number and time of the decays. There thus was no direct detection, but by observation of spontaneous fission events arising from its electron-capture daughter 256Fm. The first one was identified with a "hooray" followed by a "double hooray" and a "triple hooray". The fourth one eventually officially proved the chemical identification of the 101st element, mendelevium. In total, five decays were reported up till 4 a.m. Seaborg was notified and the team left to sleep.[4] Additional analysis and further experimentation showed the produced mendelevium isotope to have mass 256 and to decay by electron capture to fermium-256 with a half-life of 1.5 h.[2]

We thought it fitting that there be an element named for the Russian chemist Dmitri Mendeleev, who had developed the periodic table. In nearly all our experiments discovering transuranium elements, we'd depended on his method of predicting chemical properties based on the element's position in the table. But in the middle of the Cold War, naming an element for a Russian was a somewhat bold gesture that did not sit well with some American critics.[7]

— Glenn T. Seaborg

Being the first of the second hundred of the chemical elements, it was decided that the element would be named "mendelevium" after the Russian chemist Dmitri Mendeleev, father of the periodic table. Because this discovery came during the Cold War, Seaborg had to request permission of the government of the United States to propose that the element be named for a Russian, but it was granted.[4] The name "mendelevium" was accepted by the International Union of Pure and Applied Chemistry (IUPAC) in 1955 with symbol "Mv",[8] which was changed to "Md" in the next IUPAC General Assembly (Paris, 1957).[9]



Fblock fd promotion energy
Energy required to promote an f electron to the d subshell for the f-block lanthanides and actinides. Above around 210 kJ/mol, this energy is too high to be provided for by the greater crystal energy of the trivalent state and thus einsteinium, fermium, mendelevium form divalent metals like the lanthanides europium and ytterbium. (Nobelium is also expected to form a divalent metal, but this has not yet been confirmed.)[10]

In the periodic table, mendelevium is located to the right of the actinide fermium, to the left of the actinide nobelium, and below the lanthanide thulium. Mendelevium metal has not yet been prepared in bulk quantities, and bulk preparation is currently impossible.[11] Nevertheless, a number of predictions and some preliminary experimental results have been done regarding its properties.[11]

The lanthanides and actinides, in the metallic state, can exist as either divalent (such as europium and ytterbium) or trivalent (most other lanthanides) metals. The former have fnd1s2 configurations, whereas the latter have fn+1s2 configurations. In 1975, Johansson and Rosengren examined the measured and predicted values for the cohesive energies (enthalpies of crystallization) of the metallic lanthanides and actinides, both as divalent and trivalent metals.[12][13] The conclusion was that the increased binding energy of the [Rn]5f126d17s2 configuration over the [Rn]5f137s2 configuration for mendelevium was not enough to compensate for the energy needed to promote one 5f electron to 6d, as is true also for the very late actinides: thus einsteinium, fermium, mendelevium, and nobelium were expected to be divalent metals.[12] The increasing predominance of the divalent state well before the actinide series concludes is attributed to the relativistic stabilization of the 5f electrons, which increases with increasing atomic number.[14] Thermochromatographic studies with trace quantities of mendelevium by Zvara and Hübener from 1976 to 1982 confirmed this prediction.[11] In 1990, Haire and Gibson estimated mendelevium metal to have an enthalpy of sublimation between 134 and 142 kJ/mol.[11] Divalent mendelevium metal should have a metallic radius of around 194±10 pm.[11] Like the other divalent late actinides (except the once again trivalent lawrencium), metallic mendelevium should assume a face-centered cubic crystal structure.[1] Mendelevium's melting point has been estimated at 827 °C, the same value as that predicted for the neighboring element nobelium.[15] Its density is predicted to be around 10.3±0.7 g/cm3.[1]


The chemistry of mendelevium is mostly known only in solution, in which it can take on the +3 or +2 oxidation states. The +1 state has also been reported, but has not yet been confirmed.[16]

Before mendelevium's discovery, Seaborg and Katz predicted that it should be predominantly trivalent in aqueous solution and hence should behave similarly to other tripositive lanthanides and actinides. After the synthesis of mendelevium in 1955, these predictions were confirmed, first in the observation at its discovery that it eluted just after fermium in the trivalent actinide elution sequence from a cation-exchange column of resin, and later the 1967 observation that mendelevium could form insoluble hydroxides and fluorides that coprecipitated with trivalent lanthanide salts.[16] Cation-exchange and solvent extraction studies led to the conclusion that mendelevium was a trivalent actinide with an ionic radius somewhat smaller than that of the previous actinide, fermium.[16] Mendelevium can form coordination complexes with 1,2-cyclohexanedinitrilotetraacetic acid (DCTA).[16]

In reducing conditions, mendelevium(III) can be easily reduced to mendelevium(II), which is stable in aqueous solution.[16] The standard reduction potential of the E°(Md3+→Md2+) couple was variously estimated in 1967 as −0.10 V or −0.20 V:[16] later 2013 experiments established the value as −0.16±0.05 V.[17] In comparison, E°(Md3+→Md0) should be around −1.74 V, and E°(Md2+→Md0) should be around −2.5 V.[16] Mendelevium(II)'s elution behavior has been compared with that of strontium(II) and europium(II).[16]

In 1973, mendelevium(I) was reported to have been produced by Russian scientists, who obtained it by reducing higher oxidation states of mendelevium with samarium(II). It was found to be stable in neutral water–ethanol solution and be homologous to caesium(I). However, later experiments found no evidence for mendelevium(I) and found that mendelevium behaved like divalent elements when reduced, not like the monovalent alkali metals.[16] Nevertheless, the Russian team conducted further studies on the thermodynamics of cocrystallizing mendelevium with alkali metal chlorides, and concluded that mendelevium(I) had formed and could form mixed crystals with divalent elements, thus cocrystallizing with them. The status of the +1 oxidation state is still tentative.[16]

Although E°(Md4+→Md3+) was predicted in 1975 to be +5.4 V, suggesting that mendelevium(III) could be oxidized to mendelevium(IV), 1967 experiments with the strong oxidizing agent sodium bismuthate were unable to oxidize mendelevium(III) to mendelevium(IV).[16]


A mendelevium atom has 101 electrons, of which at least three (and perhaps four) can act as valence electrons. They are expected to be arranged in the configuration [Rn]5f137s2 (ground state term symbol 2F7/2), although experimental verification of this electron configuration had not yet been made as of 2006.[18] In forming compounds, three valence electrons may be lost, leaving behind a [Rn]5f12 core: this conforms to the trend set by the other actinides with their [Rn] 5fn electron configurations in the tripositive state. The first ionization potential of mendelevium was measured to be at most (6.58 ± 0.07) eV in 1974, based on the assumption that the 7s electrons would ionize before the 5f ones;[19] this value has since not yet been refined further due to mendelevium's scarcity and high radioactivity.[20] The ionic radius of hexacoordinate Md3+ had been preliminarily estimated in 1978 to be around 91.2 pm;[16] 1988 calculations based on the logarithmic trend between distribution coefficients and ionic radius produced a value of 89.6 pm, as well as an enthalpy of hydration of −3654±12 kJ/mol.[16] Md2+ should have an ionic radius of 115 pm and hydration enthalpy −1413 kJ/mol; Md+ should have ionic radius 117 pm.[16]


Sixteen isotopes of mendelevium are known, with mass numbers from 245 to 260; all are radioactive.[21] Additionally, five nuclear isomers are known: 245mMd, 247mMd, 249mMd, 254mMd, and 258mMd.[2][22] Of these, the longest-lived isotope is 258Md with a half-life of 51.5 days, and the longest-lived isomer is 258mMd with a half-life of 58.0 minutes.[2][22] Nevertheless, the slightly shorter-lived 256Md (half-life 1.17 hours) is more often used in chemical experimentation because it can be produced in larger quantities from alpha particle irradiation of einsteinium.[21] After 258Md, the next most stable mendelevium isotopes are 260Md with a half-life of 31.8 days, 257Md with a half-life of 5.52 hours, 259Md with a half-life of 1.60 hours, and 256Md with a half-life of 1.17 hours. All of the remaining mendelevium isotopes have half-lives that are less than an hour, and the majority of these have half-lives that are less than 5 minutes.[2][21][22]

The half-lives of mendelevium isotopes mostly increase smoothly from 245Md onwards, reaching a maximum at 258Md.[2][21][22] Experiments and predictions suggest that the half-lives will then decrease, apart from 260Md with a half-life of 31.8 days,[2][21][22] as spontaneous fission becomes the dominant decay mode[2] due to the mutual repulsion of the protons posing a limit to the island of relative stability of long-lived nuclei in the actinide series.[23]

Mendelevium-256, the chemically most important isotope of mendelevium, decays through electron capture 90.7% of the time and alpha decay 9.9% of the time.[21] It is most easily detected through the spontaneous fission of its electron-capture daughter fermium-256, but in the presence of other nuclides that undergo spontaneous fission, alpha decays at the characteristic energies for mendelevium-256 (7.205 and 7.139 MeV) can provide more useful identification.[24]

Production and isolation

The lightest mendelevium isotopes (245Md to 247Md) are mostly produced through bombardment of bismuth targets with heavy argon ions, while slightly heavier ones (248Md to 253Md) are produced by bombarding plutonium and americium targets with lighter ions of carbon and nitrogen. The most important and most stable isotopes are in the range from 254Md to 258Md and are produced through bombardment of einsteinium isotopes with alpha particles: einsteinium-253, -254, and -255 can all be used. 259Md is produced as a daughter of 259No, and 260Md can be produced in a transfer reaction between einsteinium-254 and oxygen-18.[21] Typically, the most commonly used isotope 256Md is produced by bombarding either einsteinium-253 or -254 with alpha particles: einsteinium-254 is preferred when available because it has a longer half-life and therefore can be used as a target for longer.[21] Using available microgram quantities of einsteinium, femtogram quantities of mendelevium-256 may be produced.[21]

The recoil momentum of the produced mendelevium-256 atoms is used to bring them physically far away from the einsteinium target from which they are produced, bringing them onto a thin foil of metal (usually beryllium, aluminium, platinum, or gold) just behind the target in a vacuum.[24] This eliminates the need for immediate chemical separation, which is both costly and prevents reusing of the expensive einsteinium target.[24] The mendelevium atoms are then trapped in a gas atmosphere (frequently helium), and a gas jet from a small opening in the reaction chamber carries the mendelevium along.[24] Using a long capillary tube, and including potassium chloride aerosols in the helium gas, the mendelevium atoms can be transported over tens of meters to be chemically analyzed and have their quantity determined.[6][24] The mendelevium can then be separated from the foil material and other fission products by applying acid to the foil and then coprecipitating the mendelevium with lanthanum fluoride, then using a cation-exchange resin column with a 10% ethanol solution saturated with hydrochloric acid, acting as an eluant. However, if the foil is made of gold and thin enough, it is enough to simply dissolve the gold in aqua regia before separating the trivalent actinides from the gold using anion-exchange chromatography, the eluant being 6 M hydrochloric acid.[24]

Mendelevium can finally be separated from the other trivalent actinides using selective elution from a cation-exchange resin column, the eluant being ammonia α-HIB.[24] Using the gas-jet method often renders the first two steps unnecessary.[24] The above procedure is the most commonly used one for the separation of transeinsteinium elements.[24]

Another possible way to separate the trivalent actinides is via solvent extraction chromatography using bis-(2-ethylhexyl) phosphoric acid (abbreviated as HDEHP) as the stationary organic phase and nitric acid as the mobile aqueous phase. The actinide elution sequence is reversed from that of the cation-exchange resin column, so that the heavier actinides elute later. The mendelevium separated by this method has the advantage of being free of organic complexing agent compared to the resin column; the disadvantage is that mendelevium then elutes very late in the elution sequence, after fermium.[6][24]

Another method to isolate mendelevium exploits the distinct elution properties of Md2+ from those of Es3+ and Fm3+. The initial steps are the same as above, and employs HDEHP for extraction chromatography, but coprecipitates the mendelevium with terbium fluoride instead of lanthanum fluoride. Then, 50 mg of chromium is added to the mendelevium to reduce it to the +2 state in 0.1 M hydrochloric acid with zinc or mercury.[24] The solvent extraction then proceeds, and while the trivalent and tetravalent lanthanides and actinides remain on the column, mendelevium(II) does not and stays in the hydrochloric acid. It is then reoxidized to the +3 state using hydrogen peroxide and then isolated by selective elution with 2 M hydrochloric acid (to remove impurities, including chromium) and finally 6 M hydrochloric acid (to remove the mendelevium).[24] It is also possible to use a column of cationite and zinc amalgam, using 1 M hydrochloric acid as an eluant, reducing Md(III) to Md(II) where it behaves like the alkaline earth metals.[24] Thermochromatographic chemical isolation could be achieved using the volatile mendelevium hexafluoroacetylacetonate: the analogous fermium compound is also known and is also volatile.[24]


Although few people come in contact with mendelevium, the International Commission on Radiological Protection has set annual exposure limits for the most stable isotope. For mendelevium-258, the ingestion limit was set at 9×105 becquerels (1 Bq is equivalent to one decay per second), and the inhalation limit at 6000 Bq.[25]


  1. ^ a b c d Fournier, Jean-Marc (1976). "Bonding and the electronic structure of the actinide metals". Journal of Physics and Chemistry of Solids. 37 (2): 235–244. Bibcode:1976JPCS...37..235F. doi:10.1016/0022-3697(76)90167-0.
  2. ^ a b c d e f g h i Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
  3. ^ a b c d Ghiorso, A.; Harvey, B.; Choppin, G.; Thompson, S.; Seaborg, Glenn T. (1955). "New Element Mendelevium, Atomic Number 101". Physical Review. 98 (5): 1518–1519. Bibcode:1955PhRv...98.1518G. doi:10.1103/PhysRev.98.1518. ISBN 9789810214401.
  4. ^ a b c d e f g h Choppin, Gregory R. (2003). "Mendelevium". Chemical and Engineering News. 81 (36).
  5. ^ Hofmann, Sigurd (2002). On beyond uranium: journey to the end of the periodic table. CRC Press. pp. 40–42. ISBN 0-415-28496-1.
  6. ^ a b c Hall, Nina (2000). The new chemistry. Cambridge University Press. pp. 9–11. ISBN 0-521-45224-4.
  7. ^ 101. Mendelevium - Elementymology & Elements Multidict. Peter van der Krogt.
  8. ^ Chemistry, International Union of Pure and Applied (1955). Comptes rendus de la confèrence IUPAC.
  9. ^ Chemistry, International Union of Pure and Applied (1957). Comptes rendus de la confèrence IUPAC.
  10. ^ Haire, Richard G. (2006). "Einsteinium". In Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean. The Chemistry of the Actinide and Transactinide Elements (PDF). 3 (3rd ed.). Dordrecht, the Netherlands: Springer. pp. 1577–1620. doi:10.1007/1-4020-3598-5_12.
  11. ^ a b c d e Silva, pp. 1634–5
  12. ^ a b Silva, pp. 1626–8
  13. ^ Johansson, Börje; Rosengren, Anders (1975). "Generalized phase diagram for the rare-earth elements: Calculations and correlations of bulk properties". Physical Review B. 11 (8): 2836–2857. Bibcode:1975PhRvB..11.2836J. doi:10.1103/PhysRevB.11.2836.
  14. ^ Hulet, E. K. (1980). "Chapter 12. Chemistry of the Heaviest Actinides: Fermium, Mendelevium, Nobelium, and Lawrencium". In Edelstein, Norman M. Lanthanide and Actinide Chemistry and Spectroscopy. doi:10.1021/bk-1980-0131.ch012. ISBN 9780841205680.
  15. ^ Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). CRC Press. pp. 4.121–4.123. ISBN 1439855110.
  16. ^ a b c d e f g h i j k l m n Silva, pp. 1635–6
  17. ^ Toyoshima, Atsushi; Li, Zijie; Asai, Masato; Sato, Nozomi; Sato, Tetsuya K.; Kikuchi, Takahiro; Kaneya, Yusuke; Kitatsuji, Yoshihiro; Tsukada, Kazuaki; Nagame, Yuichiro; Schädel, Matthias; Ooe, Kazuhiro; Kasamatsu, Yoshitaka; Shinohara, Atsushi; Haba, Hiromitsu; Even, Julia (11 October 2013). "Measurement of the Md3+/Md2+ Reduction Potential Studied with Flow Electrolytic Chromatography". Inorganic Chemistry. 52 (21): 12311–3. doi:10.1021/ic401571h.
  18. ^ Silva, pp. 1633–4
  19. ^ Martin, W. C.; Hagan, Lucy; Reader, Joseph; Sugan, Jack (1974). "Ground Levels and Ionization Potentials for Lanthanide and Actinide Atoms and Ions" (PDF). J. Phys. Chem. Ref. Data. 3 (3): 771–9. Bibcode:1974JPCRD...3..771M. doi:10.1063/1.3253147. Archived from the original (PDF) on 2014-02-11. Retrieved 2013-10-19.
  20. ^ David R. Lide (ed), CRC Handbook of Chemistry and Physics, 84th Edition. CRC Press. Boca Raton, Florida, 2003; Section 10, Atomic, Molecular, and Optical Physics; Ionization Potentials of Atoms and Atomic Ions
  21. ^ a b c d e f g h i Silva, pp. 1630–1
  22. ^ a b c d e Nucleonica (2007–2014). "Universal Nuclide Chart". Nucleonica. Retrieved 22 May 2011.
  23. ^ Nurmia, Matti (2003). "Nobelium". Chemical and Engineering News. 81 (36).
  24. ^ a b c d e f g h i j k l m n Silva, pp. 1631–3
  25. ^ Koch, Lothar (2000). Transuranium Elements, in Ullmann's Encyclopedia of Industrial Chemistry. Wiley. doi:10.1002/14356007.a27_167.


Further reading

  • Hoffman, D.C., Ghiorso, A., Seaborg, G. T. The transuranium people: the inside story, (2000), 201–229
  • Morss, L. R., Edelstein, N. M., Fuger, J., The chemistry of the actinide and transactinide element, 3, (2006), 1630–1636
  • A Guide to the Elements – Revised Edition, Albert Stwertka, (Oxford University Press; 1998) ISBN 0-19-508083-1

External links


Einsteinium is a synthetic element with symbol Es and atomic number 99. A member of the actinide series, it is the seventh transuranic element.

Einsteinium was discovered as a component of the debris of the first hydrogen bomb explosion in 1952, and named after Albert Einstein. Its most common isotope einsteinium-253 (half-life 20.47 days) is produced artificially from decay of californium-253 in a few dedicated high-power nuclear reactors with a total yield on the order of one milligram per year. The reactor synthesis is followed by a complex process of separating einsteinium-253 from other actinides and products of their decay. Other isotopes are synthesized in various laboratories, but at much smaller amounts, by bombarding heavy actinide elements with light ions. Owing to the small amounts of produced einsteinium and the short half-life of its most easily produced isotope, there are currently almost no practical applications for it outside basic scientific research. In particular, einsteinium was used to synthesize, for the first time, 17 atoms of the new element mendelevium in 1955.

Einsteinium is a soft, silvery, paramagnetic metal. Its chemistry is typical of the late actinides, with a preponderance of the +3 oxidation state; the +2 oxidation state is also accessible, especially in solids. The high radioactivity of einsteinium-253 produces a visible glow and rapidly damages its crystalline metal lattice, with released heat of about 1000 watts per gram. Difficulty in studying its properties is due to einsteinium-253's decay to berkelium-249 and then californium-249 at a rate of about 3% per day. The isotope of einsteinium with the longest half-life, einsteinium-252 (half-life 471.7 days) would be more suitable for investigation of physical properties, but it has proven far more difficult to produce and is available only in minute quantities, and not in bulk. Einsteinium is the element with the highest atomic number which has been observed in macroscopic quantities in its pure form, and this was the common short-lived isotope einsteinium-253.Like all synthetic transuranic elements, isotopes of einsteinium are very radioactive and are considered highly dangerous to health on ingestion.

Extended periodic table

An extended periodic table theorizes about chemical elements beyond those currently known in the periodic table and proven up through oganesson, which completes the seventh period (row) in the periodic table at atomic number (Z) 118.

If further elements with higher atomic numbers than this are discovered, they will be placed in additional periods, laid out (as with the existing periods) to illustrate periodically recurring trends in the properties of the elements concerned. Any additional periods are expected to contain a larger number of elements than the seventh period, as they are calculated to have an additional so-called g-block, containing at least 18 elements with partially filled g-orbitals in each period.An eight-period table containing this block was suggested by Glenn T. Seaborg in 1969. The first element of the g-block may have atomic number 121, and thus would have the systematic name unbiunium. Despite many searches, no elements in this region have been synthesized or discovered in nature.According to the orbital approximation in quantum mechanical descriptions of atomic structure, the g-block would correspond to elements with partially filled g-orbitals, but spin-orbit coupling effects reduce the validity of the orbital approximation substantially for elements of high atomic number. While Seaborg's version of the extended period had the heavier elements following the pattern set by lighter elements, as it did not take into account relativistic effects, models that take relativistic effects into account do not. Pekka Pyykkö and Burkhard Fricke used computer modeling to calculate the positions of elements up to Z = 172, and found that several were displaced from the Madelung rule. As a result of uncertainty and variability in predictions of chemical and physical properties of elements beyond 120, there is currently no consensus on their placement in the extended periodic table.

Elements in this region are likely to be highly unstable with respect to radioactive decay and undergo alpha decay or spontaneous fission with extremely short half-lives, though element 126 is hypothesized to be within an island of stability that is resistant to fission but not to alpha decay. Other islands of stability beyond the known elements may also be possible, including one theorized around element 164, though the extent of stabilizing effects from closed nuclear shells is uncertain. It is not clear how many elements beyond the expected island of stability are physically possible, whether period 8 is complete, or if there is a period 9. The International Union of Pure and Applied Chemistry (IUPAC) defines an element to exist if its lifetime is longer than 10−14 seconds (0.01 picoseconds, or 10 femtoseconds), which is the time it takes for the nucleus to form an electron cloud.As early as 1940, it was noted that a simplistic interpretation of the relativistic Dirac equation runs into problems with electron orbitals at Z > 1/α ≈ 137, suggesting that neutral atoms cannot exist beyond element 137, and that a periodic table of elements based on electron orbitals therefore breaks down at this point. On the other hand, a more rigorous analysis calculates the analogous limit to be Z ≈ 173 where the 1s subshell dives into the Dirac sea, and that it is instead not neutral atoms that cannot exist beyond element 173, but bare nuclei, thus posing no obstacle to the further extension of the periodic system. Atoms beyond this critical atomic number are called supercritical atoms.


Fermium is a synthetic element with symbol Fm and atomic number 100. It is an actinide and the heaviest element that can be formed by neutron bombardment of lighter elements, and hence the last element that can be prepared in macroscopic quantities, although pure fermium metal has not yet been prepared. A total of 19 isotopes are known, with 257Fm being the longest-lived with a half-life of 100.5 days.

It was discovered in the debris of the first hydrogen bomb explosion in 1952, and named after Enrico Fermi, one of the pioneers of nuclear physics. Its chemistry is typical for the late actinides, with a preponderance of the +3 oxidation state but also an accessible +2 oxidation state. Owing to the small amounts of produced fermium and all of its isotopes having relatively short half-lives, there are currently no uses for it outside basic scientific research.

Gregory Robert Choppin

Gregory R. Choppin (November 9, 1927, Texas, United States – October 21, 2015, Tallahassee, Florida) was an American nuclear chemist and co-discoverer of the element Mendelevium, atomic number 101 Others in the discovery group were Albert Ghiorso, Bernard G. Harvey, Stanley G. Thompson, and Glenn T. Seaborg. The element was named in honor of Dmitri Mendeleev.Choppin received a Bachelor of Science degree at Loyola University New Orleans and earned his doctorate at the University of Texas in 1953. He then worked as a Postdoctoral researcher at the University of California, Berkeley from 1953-1956.

While at Berkeley he co-discovered mendelevium. Video documentation of the discovery was produced by the television station KQED and can be viewed on YouTube with a new narration by Claude Lyneis.He taught at Florida State University from 1956 until 2001. At Florida State University, he served as Chair of the Department of Chemistry and Biochemistry and was named Robert O. Lawton Distinguished Professor, "...the highest honor the Florida State faculty bestows upon one of its own."The chemistry wing of the science building at Loyola University is named for Choppin, and the Gregory R. Choppin Chair in Chemistry and Biochemistry is an endowed chair at Florida State University.Choppin is sometimes credited with co-discovering the elements einsteinium and fermium.

Group 10 element

Group 10, numbered by current IUPAC style, is the group of chemical elements in the periodic table that consists of nickel (Ni), palladium (Pd), platinum (Pt), and perhaps also the chemically uncharacterized darmstadtium (Ds). All are d-block transition metals. All known isotopes of darmstadtium are radioactive with short half-lives, and are not known to occur in nature; only minute quantities have been synthesized in laboratories.

Like other groups, the members of this group show patterns in electron configuration, especially in the outermost shells, although for this group they are particularly weak, with palladium being an exceptional case. The relativistic stabilization of the 7s orbital is the explanation to the predicted electron configuration of darmstadtium, which, unusually for this group, conforms to that predicted by the Aufbau principle.

Group 9 element

Group 9, numbered by IUPAC nomenclature, is a group of chemical element in the periodic table. Members are cobalt (Co), rhodium (Rh), iridium (Ir) and perhaps also the chemically uncharacterized meitnerium (Mt). These are all transition metals in the d-block. All known isotopes of meitnerium are radioactive with short half-lives, and it is not known to occur in nature; only minute quantities have been synthesized in laboratories.

Like other groups, the members of this family show patterns in electron configuration, especially in the outermost shells, resulting in trends in chemical behavior; however, rhodium deviates from the pattern.

Heavy metals

Heavy metals are generally defined as metals with relatively high densities, atomic weights, or atomic numbers. The criteria used, and whether metalloids are included, vary depending on the author and context. In metallurgy, for example, a heavy metal may be defined on the basis of density, whereas in physics the distinguishing criterion might be atomic number, while a chemist would likely be more concerned with chemical behaviour. More specific definitions have been published, but none of these have been widely accepted. The definitions surveyed in this article encompass up to 96 out of the 118 known chemical elements; only mercury, lead and bismuth meet all of them. Despite this lack of agreement, the term (plural or singular) is widely used in science. A density of more than 5 g/cm3 is sometimes quoted as a commonly used criterion and is used in the body of this article.

The earliest known metals—common metals such as iron, copper, and tin, and precious metals such as silver, gold, and platinum—are heavy metals. From 1809 onwards, light metals, such as magnesium, aluminium, and titanium, were discovered, as well as less well-known heavy metals including gallium, thallium, and hafnium.

Some heavy metals are either essential nutrients (typically iron, cobalt, and zinc), or relatively harmless (such as ruthenium, silver, and indium), but can be toxic in larger amounts or certain forms. Other heavy metals, such as cadmium, mercury, and lead, are highly poisonous. Potential sources of heavy metal poisoning include mining, tailings, industrial wastes, agricultural runoff, occupational exposure, paints and treated timber.

Physical and chemical characterisations of heavy metals need to be treated with caution, as the metals involved are not always consistently defined. As well as being relatively dense, heavy metals tend to be less reactive than lighter metals and have much less soluble sulfides and hydroxides. While it is relatively easy to distinguish a heavy metal such as tungsten from a lighter metal such as sodium, a few heavy metals, such as zinc, mercury, and lead, have some of the characteristics of lighter metals, and, lighter metals such as beryllium, scandium, and titanium, have some of the characteristics of heavier metals.

Heavy metals are relatively scarce in the Earth's crust but are present in many aspects of modern life. They are used in, for example, golf clubs, cars, antiseptics, self-cleaning ovens, plastics, solar panels, mobile phones, and particle accelerators.

Inorganic compounds by element

This is a list of common inorganic and organometallic compounds of each element. Compounds are listed alphabetically by their chemical element name rather than by symbol, as in list of inorganic compounds.

Isotopes of mendelevium

Mendelevium (101Md) is a synthetic element, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was 256Md (which was also the first isotope of any element produced one atom at a time) in 1955. There are 16 known radioisotopes, ranging in atomic mass from 245Md to 260Md, and 5 isomers. The longest-lived isotope is 258Md with a half-life of 51.3 days, and the longest-lived isomer is 258mMd with a half-life of 57 minutes.

List of chemical elements naming controversies

The currently accepted names and symbols of the chemical elements are determined by the International Union of Pure and Applied Chemistry (IUPAC), usually following recommendations by the recognized discoverers of each element. However the names of several elements have been the subject of controversies until IUPAC established an official name. In most cases the controversy was due to a priority dispute as to who first found conclusive evidence for the existence of an element, or as to what evidence was in fact conclusive.

Major actinide

Major actinides is a term used in the nuclear power industry that refers to the plutonium and uranium present in used nuclear fuel, as opposed to the minor actinides neptunium, americium, curium, berkelium, and californium.

Minor actinide

The minor actinides are the actinide elements in used nuclear fuel other than uranium and plutonium, which are termed the major actinides. The minor actinides include neptunium (element 93), americium (element 95), curium (element 96), berkelium (element 97), californium (element 98), einsteinium (element 99), and fermium (element 100). The most important isotopes in spent nuclear fuel are neptunium-237, americium-241, americium-243, curium-242 through -248, and californium-249 through -252.

Plutonium and the minor actinides will be responsible for the bulk of the radiotoxicity and heat generation of used nuclear fuel in the medium term (300 to 20,000 years in the future).The plutonium from a power reactor tends to have a greater amount of Pu-241 than the plutonium generated by the lower burnup operations designed to create weapons-grade plutonium. Because the reactor-grade plutonium contains so much Pu-241 the presence of americium-241 makes the plutonium less suitable for making a nuclear weapon. The ingrowth of americium in plutonium is one of the methods for identifying the origin of an unknown sample of plutonium and the time since it was last separated chemically from the americium.

Americium is commonly used in industry as both an alpha particle and as a low photon energy gamma radiation source. For instance it is used in many smoke detectors. Americium can be formed by neutron capture of Pu-239 and Pu-240 forming Pu-241 which then beta decays to Am-241. In general, as the energy of the neutrons increases, the ratio of the fission cross section to the neutron capture cross section changes in favour of fission. Hence if MOX is used in a thermal reactor such as a boiling water reactor (BWR) or pressurized water reactor (PWR) then more americium can be expected in the used fuel than that from a fast neutron reactor.Some of the minor actinides have been found in fallout from bomb tests. See Actinides in the environment for details.


Nobelium is a synthetic chemical element with symbol No and atomic number 102. It is named in honor of Alfred Nobel, the inventor of dynamite and benefactor of science. A radioactive metal, it is the tenth transuranic element and is the penultimate member of the actinide series. Like all elements with atomic number over 100, nobelium can only be produced in particle accelerators by bombarding lighter elements with charged particles. A total of twelve nobelium isotopes are known to exist; the most stable is 259No with a half-life of 58 minutes, but the shorter-lived 255No (half-life 3.1 minutes) is most commonly used in chemistry because it can be produced on a larger scale.

Chemistry experiments have confirmed that nobelium behaves as a heavier homolog to ytterbium in the periodic table. The chemical properties of nobelium are not completely known: they are mostly only known in aqueous solution. Before nobelium's discovery, it was predicted that it would show a stable +2 oxidation state as well as the +3 state characteristic of the other actinides: these predictions were later confirmed, as the +2 state is much more stable than the +3 state in aqueous solution and it is difficult to keep nobelium in the +3 state.

In the 1950s and 1960s, many claims of the discovery of nobelium were made from laboratories in Sweden, the Soviet Union, and the United States. Although the Swedish scientists soon retracted their claims, the priority of the discovery and therefore the naming of the element was disputed between Soviet and American scientists, and it was not until 1997 that International Union of Pure and Applied Chemistry (IUPAC) credited the Soviet team with the discovery, but retained nobelium, the Swedish proposal, as the name of the element due to its long-standing use in the literature.

Period 7 element

A period 7 element is one of the chemical elements in the seventh row (or period) of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The seventh period contains 32 elements, tied for the most with period 6, beginning with francium and ending with oganesson, the heaviest element currently discovered. As a rule, period 7 elements fill their 7s shells first, then their 5f, 6d, and 7p shells, in that order; however, there are exceptions, such as plutonium.


Seaborgium is a synthetic chemical element with symbol Sg and atomic number 106. It is named after the American nuclear chemist Glenn T. Seaborg. As a synthetic element, it can be created in a laboratory but is not found in nature. It is also radioactive; the most stable known isotope, 269Sg, has a half-life of approximately 14 minutes.In the periodic table of the elements, it is a d-block transactinide element. It is a member of the 7th period and belongs to the group 6 elements as the fourth member of the 6d series of transition metals. Chemistry experiments have confirmed that seaborgium behaves as the heavier homologue to tungsten in group 6. The chemical properties of seaborgium are characterized only partly, but they compare well with the chemistry of the other group 6 elements.

In 1974, a few atoms of seaborgium were produced in laboratories in the Soviet Union and in the United States. The priority of the discovery and therefore the naming of the element was disputed between Soviet and American scientists, and it was not until 1997 that International Union of Pure and Applied Chemistry (IUPAC) established seaborgium as the official name for the element. It is one of only two elements named after a living person at the time of naming, the other being oganesson, element 118.

Synthetic element

In chemistry, a synthetic element is a chemical element that does not occur naturally on Earth, and can only be created artificially. So far, 24 synthetic elements have been created (those with atomic numbers 95–118). All are unstable, decaying with half-lives ranging from 15.6 million years to a few hundred microseconds.

Seven other elements were first created artificially and thus considered synthetic, but later discovered to exist naturally (in trace quantities) as well; among them plutonium—first synthesized in 1940—the one best known to laypeople, because of its use in atomic bombs and nuclear reactors.

Transfermium Wars

The names for the chemical elements 104 to 106 were the subject of a major controversy starting in the 1960s, described by some nuclear chemists as the Transfermium Wars because it concerned the elements following fermium (element 100) on the periodic table.

This controversy arose from disputes between American scientists and Soviet scientists as to which had first isolated these elements. The final resolution of this controversy in 1997 also decided the names of elements 107 to 109.

Transuranium element

The transuranium elements (also known as transuranic elements) are the chemical elements with atomic numbers greater than 92, which is the atomic number of uranium. All of these elements are unstable and decay radioactively into other elements.

Unu (disambiguation)

unu was a Romanian art magazine published from 1928 to 1935.

UNU or Unu may also refer to:

United Nations University, the academic and research arm of the United Nations, established in 1973 and based in Tokyo, Japan

University of Nottingham Students' Union, formerly called University of Nottingham Union

Unnilunium (Unu), the IUPAC systematic name for chemical element 101, Mendelevium (symbol: Md)

Unu River, Romania

Unu (Star Wars), a fictional race in the Star Wars universe

unu, a command-line utility for managing files in the nrrd format

Oenoë (alternate spelling Unu), an Indonesian principality in Aceh

UNU social platform

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