Lawrencium

Lawrencium is a synthetic chemical element with symbol Lr (formerly Lw) and atomic number 103. It is named in honor of Ernest Lawrence, inventor of the cyclotron, a device that was used to discover many artificial radioactive elements. A radioactive metal, lawrencium is the eleventh transuranic element and is also the final member of the actinide series. Like all elements with atomic number over 100, lawrencium can only be produced in particle accelerators by bombarding lighter elements with charged particles. Twelve isotopes of lawrencium are currently known; the most stable is 266Lr with a half-life of 11 hours, but the shorter-lived 260Lr (half-life 2.7 minutes) is most commonly used in chemistry because it can be produced on a larger scale.

Chemistry experiments have confirmed that lawrencium behaves as a heavier homolog to lutetium in the periodic table, and is a trivalent element. It thus could also be classified as the first of the 7th-period transition metals: however, its electron configuration is anomalous for its position in the periodic table, having an s2p configuration instead of the s2d configuration of its homolog lutetium. This means that lawrencium may be more volatile than expected for its position in the periodic table and have a volatility comparable to that of lead.

In the 1950s, 1960s, and 1970s, many claims of the synthesis of lawrencium of varying quality were made from laboratories in the Soviet Union and the United States. The priority of the discovery and therefore the naming of the element was disputed between Soviet and American scientists, and while the International Union of Pure and Applied Chemistry (IUPAC) initially established lawrencium as the official name for the element and gave the American team credit for the discovery, this was reevaluated in 1997, giving both teams shared credit for the discovery but not changing the element's name.

Lawrencium,  103Lr
Lawrencium
Pronunciation/ləˈrɛnsiəm/ (listen) (lə-REN-see-əm)
Appearancesilvery (predicted)[1]
Mass number266 (most stable isotope)
Lawrencium 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
Lu

Lr

(Ups)
nobeliumlawrenciumrutherfordium
Atomic number (Z)103
Groupgroup n/a
Periodperiod 7
Blockf-block
Element category  actinide, sometimes considered a transition metal
Electron configuration[Rn] 5f14 7s2 7p1
Electrons per shell
2, 8, 18, 32, 32, 8, 3
Physical properties
Phase at STPunknown phase (predicted)
Melting point1900 K ​(1627 °C, ​2961 °F) (predicted)
Density (near r.t.)~15.6–16.6 g/cm3 (predicted)[2][3]
Atomic properties
Oxidation states+3
ElectronegativityPauling scale: 1.3 (predicted)[4]
Ionization energies
  • 1st: 478.6 kJ/mol[5]
  • 2nd: 1428.0 kJ/mol (predicted)
  • 3rd: 2219.1 kJ/mol (predicted)
Other properties
Natural occurrencesynthetic
Crystal structurehexagonal close-packed (hcp)
Hexagonal close-packed crystal structure for lawrencium

(predicted)[6]
CAS Number22537-19-5
History
Namingafter Ernest Lawrence
DiscoveryLawrence Berkeley National Laboratory and Joint Institute for Nuclear Research (1961–1971)
Main isotopes of lawrencium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
254Lr syn 13 s 78% α 250Md
22% ε 254No
255Lr syn 21.5 s α 251Md
256Lr syn 27 s α 252Md
259Lr syn 6.2 s 78% α 255Md
22% SF
260Lr syn 2.7 min α 256Md
261Lr syn 44 min SF/ε?
262Lr syn 3.6 h ε 262No
266Lr syn 10 h SF

History

96904536.thumb3.jpeg
Albert Ghiorso updating the periodic table in April 1961, inscribing the symbol "Lw" in the position for element 103, as codiscoverers Latimer, Sikkeland, and Larsh (left to right) look on approvingly.

In 1958, scientists at the Lawrence Berkeley National Laboratory claimed the discovery of element 102, now called nobelium. At the same time, they also attempted to synthesize element 103 by bombarding the same curium target used with nitrogen-14 ions. A follow-up on this experiment was not performed, as the target was destroyed. Eighteen tracks were noted, with decay energy around 9±MeV and half-life around ​14 s; the Berkeley team noted that while the cause could be the production of an isotope of element 103, other possibilities could not be ruled out. While the data agrees reasonably with that later discovered for 257Lr (alpha decay energy 8.87 MeV, half-life 0.6 s), the evidence obtained in this experiment fell far short of the strength required to conclusively demonstrate the synthesis of element 103.[7][8] Later, in 1960, the Lawrence Berkeley Laboratory attempted to synthesize the element by bombarding 252Cf with 10B and 11B. The results of this experiment were not conclusive.[7]

The first important work on element 103 was carried out at Berkeley by the nuclear-physics team of Albert Ghiorso, Torbjørn Sikkeland, Almon Larsh, Robert M. Latimer, and their co-workers on February 14, 1961. The first atoms of lawrencium were reportedly produced by bombarding a three-milligram target consisting of three isotopes of the element californium with boron-10 and boron-11 nuclei from the Heavy Ion Linear Accelerator (HILAC).[9] The Berkeley team reported that the isotope 257103 was detected in this manner, and that it decayed by emitting an 8.6 MeV alpha particle with a half-life of 8±2 s.[8] This identification was later corrected to be 258103,[9] as later work proved that 257Lr did not have the properties detected, but 258Lr did.[8] This was considered at the time to be convincing proof of the synthesis of element 103: while the mass assignment was less certain and proved to be mistaken, it did not affect the arguments in favor of element 103 having been synthesized. Scientists at the Joint Institute for Nuclear Research in Dubna (then in the Soviet Union) raised several criticisms: all but one were answered adequately. The exception was that 252Cf was the most common isotope in the target, and in the reactions with 10B, 258Lr could only have been produced by emitting four neutrons, and emitting three neutrons was expected to be much less likely than emitting four or five. This would lead to a narrow yield curve, not the broad one reported by the Berkeley team. A possible explanation was that there was a low number of events attributed to element 103.[8] This was an important intermediate step to the unquestioned discovery of element 103, although the evidence was not completely convincing.[8] The Berkeley team proposed the name "lawrencium" with symbol "Lw", after Ernest Orlando Lawrence, inventor of the cyclotron. The IUPAC Commission on Nomenclature of Inorganic Chemistry accepted the name, but changed the symbol to "Lr".[10] This acceptance of the discovery was later characterized as being hasty by the Dubna team.[8]

252
98
Cf
+ 11
5
B
263
103
Lr
* → 258
103
Lr
+ 5 1
0
n

The first work at Dubna on element 103 came in 1965, when they reported to have created 256103 in 1965 by bombarding 243Am with 18O, identifying it indirectly from its granddaughter fermium-252. The half-life they reported was somewhat too high, possibly due to background events. Later 1967 work on the same reaction identified two decay energies in the ranges 8.35–8.50 MeV and 8.50–8.60 MeV: these were assigned to 256103 and 257103.[8] Despite repeated attempts, they were unable to confirm assignment of an alpha emitter with a half-life of eight seconds to 257103.[11][12] The Russians proposed the name "rutherfordium" for the new element in 1967:[7] this name was later used for element 104.

243
95
Am
+ 18
8
O
261
103
Lr
* → 256
103
Lr
+ 5 1
0
n

Further experiments in 1969 at Dubna and in 1970 at Berkeley demonstrated an actinide chemistry for the new element, so that by 1970 it was known that element 103 is the last actinide.[8][13] In 1970, the Dubna group reported the synthesis of 255103 with half-life 20 s and alpha decay energy 8.38 MeV.[8] However, it was not until 1971, when the nuclear physics team at the University of California at Berkeley successfully performed a whole series of experiments aimed at measuring the nuclear decay properties of the lawrencium isotopes with mass numbers from 255 through 260,[14][15] that all previous results from Berkeley and Dubna were confirmed, apart from the Berkeley's group initial erroneous assignment of their first produced isotope to 257103 instead of the probably correct 258103.[8] All final doubts were finally dispelled in 1976 and 1977 when the energies of X-rays emitted from 258103 were measured.[8]

Ernest Lawrence
The element was named after Ernest Lawrence.

In 1971, the IUPAC granted the discovery of lawrencium to the Lawrence Berkeley Laboratory, even though they did not have ideal data for the element's existence. However, in 1992, the IUPAC Trans-fermium Working Group (TWG) officially recognized the nuclear physics teams at Dubna and Berkeley as the co-discoverers of lawrencium, concluding that while the 1961 Berkeley experiments were an important step to lawrencium's discovery, they were not yet completely convincing; and while the 1965, 1968, and 1970 Dubna experiments came very close to the needed level of confidence taken together, only the 1971 Berkeley experiments, which clarified and confirmed previous observations, finally resulted in complete confidence in the discovery of element 103.[7][10] Because the name "lawrencium" had been in use for a long time by this point, it was retained by IUPAC,[7] and in August 1997, the International Union of Pure and Applied Chemistry (IUPAC) ratified the name lawrencium and the symbol "Lr" during a meeting in Geneva.[10]

Characteristics

Physical

Lawrencium is the final member of the actinide series and is sometimes considered to be a group 3 element, along with scandium, yttrium, and lutetium, as its filled f-shell is expected to make it resemble the 7th-period transition metals. In the periodic table, it is located to the right of the actinide nobelium, to the left of the 6d transition metal rutherfordium, and under the lanthanide lutetium with which it shares many physical and chemical properties. Lawrencium is expected to be a solid under normal conditions and assume a hexagonal close-packed crystal structure (c/a = 1.58), similar to its lighter congener lutetium, though this is not yet known experimentally.[6] The enthalpy of sublimation of lawrencium is estimated to be 352 kJ/mol, close to the value of lutetium and strongly suggesting that metallic lawrencium is trivalent with the 7s and 6d electrons delocalized, a prediction also supported by a systematic extrapolation of the values of heat of vaporization, bulk modulus, and atomic volume of neighboring elements to lawrencium.[16] Specifically, lawrencium is expected to be a trivalent, silvery metal, easily oxidized by air, steam, and acids,[17] and having an atomic volume similar to that of lutetium and a trivalent metallic radius of 171 pm.[16] It is expected to be a rather heavy metal with a density of around 15.6 to 16.6 g/cm3.[2][3] It is also predicted to have a melting point of around 1900 K (1627 °C), not far from the value for lutetium (1925 K).[18]

Chemical

F-block elution sequence
Elution sequence of the late trivalent lanthanides and actinides, with ammonium α-HIB as eluant: the broken curve for lawrencium is a prediction.

In 1949, Glenn T. Seaborg, who devised the actinide concept that elements 89 to 103 formed an actinide series homologous to the lanthanide series from elements 57 to 71, predicted that element 103 (lawrencium) should be its final member and that the Lr3+ ion should be about as stable as Lu3+ in aqueous solution. It was not until decades later that element 103 was finally conclusively synthesized and this prediction was experimentally confirmed.[19]

1969 studies on the element showed that lawrencium reacted with chlorine to form a product that was most likely the trichloride LrCl3. Its volatility was found to be similar to that of the chlorides of curium, fermium, and nobelium and much less than that of rutherfordium chloride. In 1970, chemical studies were performed on 1500 atoms of the isotope 256Lr, comparing it with divalent (No, Ba, Ra), trivalent (Fm, Cf, Cm, Am, Ac), and tetravalent (Th, Pu) elements. It was found that lawrencium coextracted with the trivalent ions, but the short half-life of the 256Lr isotope precluded a confirmation that it eluted ahead of Md3+ in the elution sequence.[19] Lawrencium occurs as the trivalent Lr3+ ion in aqueous solution and hence its compounds should be similar to those of the other trivalent actinides: for example, lawrencium(III) fluoride (LrF3) and hydroxide (Lr(OH)3) should both be insoluble in water.[19] Due to the actinide contraction, the ionic radius of Lr3+ should be smaller than that of Md3+, and it should elute ahead of Md3+ when ammonium α-hydroxyisobutyrate (ammonium α-HIB) is used as an eluant.[19] Later 1987 experiments on the longer-lived isotope 260Lr confirmed lawrencium's trivalency and that it eluted in roughly the same place as erbium, and found that lawrencium's ionic radius was 88.6±0.3 pm, larger than would be expected from simple extrapolation from periodic trends.[19] Later 1988 experiments with more lawrencium atoms refined this value to 88.1±0.1 pm and calculated an enthalpy of hydration value of −3685±13 kJ/mol.[19] It was also pointed out that the actinide contraction at the end of the actinide series was larger than the analogous lanthanide contraction, with the exception of the last actinide, lawrencium: the cause was speculated to be relativistic effects.[19]

It has been speculated that the 7s electrons are relativistically stabilized, so that in reducing conditions, only the 7p1/2 or 6d electron would be ionized, leading to the monovalent Lr+ ion. However, all experiments to reduce Lr3+ to Lr2+ or Lr+ in aqueous solution were unsuccessful, similarly to lutetium. On the basis of this, the standard electrode potential of the E°(Lr3+→Lr+) couple was calculated to be less than −1.56 V, indicating that the existence of Lr+ ions in aqueous solution was unlikely. The upper limit for the E°(Lr3+→Lr2+) couple was predicted to be −0.44 V: the values for E°(Lr3+→Lr) and E°(Lr4+→Lr3+) are predicted to be −2.06 V and +7.9 V.[19] The stability of the group oxidation state in the 6d transition series decreases as RfIV > DbV > SgVI, and lawrencium continues the trend with LrIII being more stable than RfIV.[20]

In the molecule lawrencium dihydride (LrH2), which is predicted to be bent, the 6d orbital of lawrencium is not expected to play a role in the bonding, unlike that of lanthanum dihydride (LaH2). LaH2 has La–H bond distances of 2.158 Å, while LrH2 should have shorter Lr–H bond distances of 2.042 Å due to the relativistic contraction and stabilization of the 7s and 7p orbitals involved in the bonding, in contrast to the core-like 5f subshell and the mostly uninvolved 6d subshell. In general, molecular LrH2 and LrH are expected to resemble the corresponding thallium species (thallium having a 6s26p1 valence configuration in the gas phase, like lawrencium's 7s27p1) more than the corresponding lanthanide species.[21] The electron configurations of Lr+ and Lr2+ are expected to be 7s2 and 7s1 respectively, unlike the lanthanides which tend to be 5d1 as Ln2+. However, in species where all three valence electrons of lawrencium are ionized to give at least formally the Lr3+ cation, lawrencium is expected to behave like a typical actinide and the heavier congener of lutetium, especially because the first three ionization potentials of lawrencium are predicted to be similar to those of lutetium. Hence, unlike thallium but like lutetium, lawrencium would prefer to form LrH3 than LrH, and LrCO is expected to be similar to the also unknown LuCO, both metals having a valence configuration of σ2π1 in their respective monocarbonyls. The pπ–dπ bond is expected to be observed in LrCl3 just as it is for LuCl3 and more generally all the LnCl3, and the complex anion [Lr(C5H4SiMe3)3] is expected to be stable just like its lanthanide congeners, with a configuration of 6d1 for lawrencium; this 6d orbital would be its highest occupied molecular orbital.[22]

Atomic

A lawrencium atom has 103 electrons, of which three can act as valence electrons. In 1970, it was predicted that the ground-state electron configuration of lawrencium was [Rn]5f146d17s2 (ground state term symbol 2D3/2), following the Aufbau principle and conforming to the [Xe]4f145d16s2 configuration of lawrencium's lighter homolog lutetium.[23] However, the next year, calculations were published that questioned this prediction, instead expecting an anomalous [Rn]5f147s27p1 configuration.[23] Though early calculations gave conflicting results,[24] more recent studies and calculations confirm the s2p suggestion.[25][26] 1974 relativistic calculations concluded that the energy difference between the two configurations was small and that it was uncertain which was the ground state.[23] Later 1995 calculations concluded that the s2p configuration should be energetically favored, because the spherical s and p1/2 orbitals are nearest to the atomic nucleus and thus move quickly enough that their relativistic mass increases significantly.[23]

In 1988, a team of scientists led by Eichler calculated that lawrencium's enthalpy of adsorption on metal sources would differ enough depending on its electron configuration that it would be feasible to carry out experiments to exploit this fact to measure lawrencium's electron configuration.[23] The s2p configuration was expected to be more volatile than the s2d configuration, and be more similar to that of the p-block element lead. No evidence for lawrencium being volatile was obtained and the lower limit for the enthalpy of adsorption of lawrencium on quartz or platinum was significantly higher than the estimated value for the s2p configuration.[23]

In 2015, the first ionization energy of lawrencium was measured, using the isotope 256Lr.[27] The measured value, 4.96+0.08
−0.07
eV
, agreed very well with the relativistic theoretical prediction of 4.963(15) eV, and also provided a first step into measuring the first ionization energies of the transactinides.[27] This value is the lowest among all the lanthanides and actinides, and supports the s2p configuration as the 7p1/2 electron is expected to be only weakly bound. This suggests that lutetium and lawrencium behave similarly to the d-block elements (and hence being the true heavier congeners of scandium and yttrium, instead of lanthanum and actinium), and also that lawrencium may behave similarly to the alkali metals sodium and potassium in some ways.[28] Given that the s2p configuration is correct, then lawrencium cannot be regarded as a transition metal under the IUPAC definition ("An element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell"),[29] unlike its lighter homolog lutetium and the group 3 elements, with which lutetium and lawrencium are sometimes classified.[30] It is nevertheless quite likely that metallic lawrencium will behave similarly to curium, which has an [Rn]5f76d17s2 configuration, and show the expected [Rn]5f146d17s2 configuration, which is supported by the earlier volatility experiments.[31]

Isotopes

Twelve isotopes of lawrencium are known, with mass numbers 252–262 and 266; all are radioactive.[32][33] Additionally, one nuclear isomer is known, with mass number 253.[32] The longest-lived lawrencium isotope, 266Lr, has a half-life of ten hours and is one of the longest lived superheavy isotopes known to date, suggesting that it is perhaps on the shore of the island of stability of superheavy nuclei.[34] However, shorter-lived isotopes are usually used in chemical experiments because 266Lr currently can only be produced as a final decay product of even heavier and harder-to-synthesize elements: it was discovered in 2014 in the decay chain of 294Ts.[32][33] The isotope 256Lr (half-life 27 seconds) was used in the first chemical studies on lawrencium: currently, the slightly longer lived isotope 260Lr (half-life 2.7 minutes) is usually used for this purpose.[32] After 266Lr, the longest-lived lawrencium isotopes are 262Lr (3.6 h), 261Lr (44 min), 260Lr (2.7 min), 256Lr (27 s), and 255Lr (22 s).[32][35][36] All other known lawrencium isotopes have half-lives under 20 seconds, and the shortest-lived of them (252Lr) has a half-life of only 390 milliseconds.[32][35][36]However, the undiscovered isotopes with mass numbers 263 to 265 are expected to have longer half-lives (263Lr, 5 h; 264Lr and 265Lr, 10 h).[35][36] The half-lives of lawrencium isotopes mostly increase smoothly from 252Lr to 266Lr, with a dip from 257Lr to 259Lr.[32][35][36]

Preparation and purification

While the lightest (252Lr to 254Lr) and heaviest (266Lr) lawrencium isotopes are produced only as alpha decay products of dubnium (Z = 105) isotopes, the middle isotopes (255Lr to 262Lr) can all be produced by bombarding actinide (americium to einsteinium) targets with light ions (from boron to neon). The two most important isotopes, 256Lr and 260Lr, are both in this range. 256Lr can be produced by bombarding californium-249 with 70 MeV boron-11 ions (producing lawrencium-256 and four neutrons), while 260Lr can be produced by bombarding berkelium-249 with oxygen-18 (producing lawrencium-260, an alpha particle, and three neutrons).[37]

Both 256Lr and 260Lr have half-lives too short to allow a complete chemical purification process. Early experiments with 256Lr therefore used rapid solvent extraction, with the chelating agent thenoyltrifluoroacetone (TTA) dissolved in methyl isobutyl ketone (MIBK) as the organic phase, and with the aqueous phase being buffered acetate solutions. Ions of different charge (+2, +3, or +4) will then extract into the organic phase under different pH ranges, but this method will not separate the trivalent actinides and thus 256Lr must be identified by its emitted 8.24 MeV alpha particles.[37] More recent methods have allowed rapid selective elution with α-HIB to take place in enough time to separate out the longer-lived isotope 260Lr, which can be removed from the catcher foil with 0.05 M hydrochloric acid.[37]

References

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Bibliography

  • Silva, Robert J. (2011). "Chapter 13. Fermium, Mendelevium, Nobelium, and Lawrencium". In Morss, Lester R.; Edelstein, Norman M.; Fuger, Jean. The Chemistry of the Actinide and Transactinide Elements. Netherlands: Springer. doi:10.1007/978-94-007-0211-0_13. ISBN 978-94-007-0210-3.

External links

Actinide

The actinide or actinoid (IUPAC nomenclature) series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.Strictly speaking, both actinium and lawrencium have been labeled as group 3 elements, but both elements are often included in any general discussion of the chemistry of the actinide elements. Actinium is the more often omitted of the two, because its placement as a group 3 element is somewhat more common in texts and for semantic reasons: since "actinide" means "like actinium", it has been argued that actinium cannot logically be an actinide, even though IUPAC acknowledges its inclusion based on common usage.The actinide series derives its name from the first element in the series, actinium. The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide. All but one of the actinides are f-block elements, with the exception being either actinium or lawrencium. The series mostly corresponds to the filling of the 5f electron shell, although actinium and thorium lack any f-electrons, and curium and lawrencium have the same number as the preceding element. In comparison with the lanthanides, also mostly f-block elements, the actinides show much more variable valence. They all have very large atomic and ionic radii and exhibit an unusually large range of physical properties. While actinium and the late actinides (from americium onwards) behave similarly to the lanthanides, the elements thorium, protactinium, and uranium are much more similar to transition metals in their chemistry, with neptunium and plutonium occupying an intermediate position.

All actinides are radioactive and release energy upon radioactive decay; naturally occurring uranium and thorium, and synthetically produced plutonium are the most abundant actinides on Earth. These are used in nuclear reactors and nuclear weapons. Uranium and thorium also have diverse current or historical uses, and americium is used in the ionization chambers of most modern smoke detectors.

Of the actinides, primordial thorium and uranium occur naturally in substantial quantities. The radioactive decay of uranium produces transient amounts of actinium and protactinium, and atoms of neptunium and plutonium are occasionally produced from transmutation reactions in uranium ores. The other actinides are purely synthetic elements. Nuclear weapons tests have released at least six actinides heavier than plutonium into the environment; analysis of debris from a 1952 hydrogen bomb explosion showed the presence of americium, curium, berkelium, californium, einsteinium and fermium.In presentations of the periodic table, the lanthanides and the actinides are customarily shown as two additional rows below the main body of the table, with placeholders or else a selected single element of each series (either lanthanum or lutetium, and either actinium or lawrencium, respectively) shown in a single cell of the main table, between barium and hafnium, and radium and rutherfordium, respectively. This convention is entirely a matter of aesthetics and formatting practicality; a rarely used wide-formatted periodic table inserts the lanthanide and actinide series in their proper places, as parts of the table's sixth and seventh rows (periods).

Actinide chemistry

Actinide chemistry (or actinoid chemistry) is one of the main branches of nuclear chemistry that investigates the processes and molecular systems of the actinides. The actinides derive their name from the group 3 element actinium. The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide. All but one of the actinides are f-block elements, corresponding to the filling of the 5f electron shell; lawrencium, a d-block element, is also generally considered an actinide. In comparison with the lanthanides, also mostly f-block elements, the actinides show much more variable valence. The actinide series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.

Actinide concept

In nuclear chemistry, the actinide concept proposed that the actinides form a second inner transition series homologous to the lanthanides. Its origins stem from observation of lanthanide-like properties in transuranic elements in contrast to the distinct complex chemistry of previously known actinides. Glenn T. Seaborg, one of the researchers who synthesized transuranic elements, proposed the actinide concept in 1944 as an explanation for observed deviations and a hypothesis to guide future experiments. It was accepted shortly thereafter, resulting in the placement of a new actinide series comprising elements 89 (actinium) to 103 (lawrencium) below the lanthanides in Dmitri Mendeleev's periodic table of the elements.

Actinium

Actinium is a chemical element with symbol Ac and atomic number 89. It was first isolated by French chemist André-Louis Debierne in 1899. Friedrich Oskar Giesel later independently isolated it in 1902 and, unaware that it was already known, gave it the name emanium. Actinium gave the name to the actinide series, a group of 15 similar elements between actinium and lawrencium in the periodic table. It is also sometimes considered the first of the 7th-period transition metals, although lawrencium is less commonly given that position. Together with polonium, radium, and radon, actinium was one of the first non-primordial radioactive elements to be isolated.

A soft, silvery-white radioactive metal, actinium reacts rapidly with oxygen and moisture in air forming a white coating of actinium oxide that prevents further oxidation. As with most lanthanides and many actinides, actinium assumes oxidation state +3 in nearly all its chemical compounds. Actinium is found only in traces in uranium and thorium ores as the isotope 227Ac, which decays with a half-life of 21.772 years, predominantly emitting beta and sometimes alpha particles, and 228Ac, which is beta active with a half-life of 6.15 hours. One tonne of natural uranium in ore contains about 0.2 milligrams of actinium-227, and one tonne of thorium contains about 5 nanograms of actinium-228. The close similarity of physical and chemical properties of actinium and lanthanum makes separation of actinium from the ore impractical. Instead, the element is prepared, in milligram amounts, by the neutron irradiation of 226Ra in a nuclear reactor. Owing to its scarcity, high price and radioactivity, actinium has no significant industrial use. Its current applications include a neutron source and an agent for radiation therapy targeting cancer cells in the body and killing them.

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.

Group 3 element

Group 3 is a group of elements in the periodic table. This group, like other d-block groups, should contain four elements, but it is not agreed what elements belong in the group. Scandium (Sc) and yttrium (Y) are always included, but the other two spaces are usually occupied by lanthanum (La) and actinium (Ac), or by lutetium (Lu) and lawrencium (Lr); less frequently, it is considered the group should be expanded to 32 elements (with all the lanthanides and actinides included) or contracted to contain only scandium and yttrium. When the group is understood to contain all of the lanthanides, its trivial name is the rare-earth metals.

Three group 3 elements occur naturally: scandium, yttrium, and either lanthanum or lutetium. Lanthanum continues the trend started by two lighter members in general chemical behavior, while lutetium behaves more similarly to yttrium. While the choice of lutetium would be in accordance with the trend for period 6 transition metals to behave more similarly to their upper periodic table neighbors, the choice of lanthanum is in accordance with the trends in the s-block, which the group 3 elements are chemically more similar to. They all are silvery-white metals under standard conditions. The fourth element, either actinium or lawrencium, has only radioactive isotopes. Actinium, which occurs only in trace amounts, continues the trend in chemical behavior for metals that form tripositive ions with a noble gas configuration; synthetic lawrencium is calculated and partially shown to be more similar to lutetium and yttrium. So far, no experiments have been conducted to synthesize any element that could be the next group 3 element. Unbiunium (Ubu), which could be considered a group 3 element if preceded by lanthanum and actinium, might be synthesized in the near future, it being only three spaces away from the current heaviest element known, oganesson.

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 lawrencium

Lawrencium (103Lr) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was 258Lr in 1961. There are twelve known radioisotopes from 252Lr to 266Lr, and 1 isomer (253mLr). The longest-lived isotope is 266Lr with a half-life of 11 hours. Heavier isotopes are expected to have longer half-lives.

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.

Nobelium

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.

Periodic table

The periodic table, also known as the periodic table of elements, is a tabular display of the chemical elements, which are arranged by atomic number, electron configuration, and recurring chemical properties. The structure of the table shows periodic trends. The seven rows of the table, called periods, generally have metals on the left and non-metals on the right. The columns, called groups, contain elements with similar chemical behaviours. Six groups have accepted names as well as assigned numbers: for example, group 17 elements are the halogens; and group 18 are the noble gases. Also displayed are four simple rectangular areas or blocks associated with the filling of different atomic orbitals.

The organization of the periodic table can be used to derive relationships between the various element properties, and also to predict chemical properties and behaviours of undiscovered or newly synthesized elements. Russian chemist Dmitri Mendeleev published the first recognizable periodic table in 1869, developed mainly to illustrate periodic trends of the then-known elements. He also predicted some properties of unidentified elements that were expected to fill gaps within the table. Most of his forecasts proved to be correct. Mendeleev's idea has been slowly expanded and refined with the discovery or synthesis of further new elements and the development of new theoretical models to explain chemical behaviour. The modern periodic table now provides a useful framework for analyzing chemical reactions, and continues to be widely used in chemistry, nuclear physics and other sciences.

The elements from atomic numbers 1 (hydrogen) through 118 (oganesson) have been discovered or synthesized, completing seven full rows of the periodic table. The first 94 elements all occur naturally, though some are found only in trace amounts and a few were discovered in nature only after having first been synthesized. Elements 95 to 118 have only been synthesized in laboratories or nuclear reactors. The synthesis of elements having higher atomic numbers is currently being pursued: these elements would begin an eighth row, and theoretical work has been done to suggest possible candidates for this extension. Numerous synthetic radionuclides of naturally occurring elements have also been produced in laboratories.

Periodic table (detailed cells)

The periodic table is a tabular method of displaying the chemical elements. It can show much information, after name, symbol and atomic number. Also, for each element mean atomic mass value for the natural isotopic composition of each element can be noted.

The two layout forms originate from two graphic forms of presentation of the same periodic table. Historically, when the f-block was identified it was drawn below the existing table, with markings for its in-table location (this page uses dots or asterisks). Also, a common presentation is to put all 15 lanthanide and actinide columns below, while the f-block only has 14 columns. One lanthanide and actinide each are d-block elements, belonging to group 3 with scandium and yttrium, though whether these are the first of each series (lanthanum and actinium) or the last (lutetium and lawrencium) has been disputed. The tables below show lanthanum and actinium as group 3 elements, as this is the more common form in the literature.

Although precursors to this table exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869. Mendeleev invented the table to illustrate recurring ("periodic") trends in the properties of the elements. The layout of the table has been refined and extended over time, as new elements have been discovered, and new theoretical models have been developed to explain chemical behavior.

Seaborgium

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.

Transactinide element

In chemistry, transactinide elements (also transactinides, superheavy elements, or super-heavy elements) are the chemical elements with atomic numbers from 104 to 120. Their atomic numbers are immediately greater than those of the actinides, the heaviest of which is lawrencium (atomic number 103).

Glenn T. Seaborg first proposed the actinide concept, which led to the acceptance of the actinide series. He also proposed the transactinide series ranging from element 104 to 121 and the superactinide series approximately spanning elements 122 to 153. The transactinide seaborgium was named in his honor.By definition, transactinide elements are also transuranic elements, i.e. have an atomic number greater than uranium (92).

The transactinide elements all have electrons in the 6d subshell in their ground state. Except for rutherfordium and dubnium, even the longest-lasting isotopes of transactinide elements have extremely short half-lives of minutes or less. The element naming controversy involved the first five or six transactinide elements. These elements thus used systematic names for many years after their discovery had been confirmed. (Usually the systematic names are replaced with permanent names proposed by the discoverers relatively shortly after a discovery has been confirmed.)

Transactinides are radioactive and have only been obtained synthetically in laboratories. None of these elements have ever been collected in a macroscopic sample. Transactinide elements are all named after physicists and chemists or important locations involved in the synthesis of the elements.

IUPAC defines an element to exist if its lifetime is longer than 10−14 seconds, which is the time it takes for the nucleus to form an electron cloud.

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.

UNT (disambiguation)

UNT can refer to:

Un Nuevo Tiempo ("A New Era"), a political party in Venezuela

Unión Nacional de Trabajadores (disambiguation), national trade union federations in several countries

Union Nationale Tchadienne, a radical Islamic political party in Chad

Universidad Nacional de Tucumán, a national university in Argentina

University of North Texas, a state university in Denton, Texas

Unt, abbreviation for unniltrium, another name for chemical element 103, Lawrencium

Upsala Nya Tidning, a Swedish newspaper.

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