Uranium (U)
actinideSolid
Peso atomico standard
238,02891 uConfigurazione elettronica
[Rn] 7s2 5f3 6d1Punto di fusione
1134,85 °CPunto di ebollizione
4130,85 °CDensità
1,895e+4 kg/m³Stati di ossidazione
−1, +1, +2, +3, +4, +5, +6Elettronegatività (Pauling)
1,38Energia di ionizzazione (1ª)
6,19405 eVAnno della scoperta
1789Raggio atomico
175 pmDettagli
Uranium is a dense actinide metal and the heaviest element found in substantial natural abundance on Earth. Natural uranium is dominated by ²³⁸U, with smaller amounts of fissile ²³⁵U and trace ²³⁴U. Its chemistry is strongly oxophilic and commonly involves the uranyl ion, UO₂²⁺. Uranium is technologically important as nuclear fuel and historically important in the discovery and development of radioactivity and nuclear fission.
Pure uranium is a silvery white, weakly radioactive metal, which is harder than most elements. It is malleable, ductile, slightly paramagnetic, strongly electropositive and is a poor electrical conductor. Uranium metal has very high density, being approximately 70% denser than lead, but slightly less dense than gold. Uranium metal exhibits in three crystallographic modifications: alpha > (688°C) > beta > (776°C) > gamma. Uranium is pyrophoric when finely divided. It is a little softer than steel and is attacked by cold water in a finely divided state.In air, uranium metal becomes coated with a layer of oxide. Acids dissolve the metal, forming the +3 oxidation state which oxidizes rapidly by water and air to form higher oxidation states. Uranium metal is unaffected by alkalis. Uranium metal can be prepared by reducing uranium halides with alkali or alkaline earth metals or by reducing uranium oxides by calcium, aluminum, or carbon at high temperatures. The metal can also be produced by electrolysis of KUF5 or UF4, dissolved in a molten salt mixture of CaCl2 and NaCl. High-purity uranium can be prepared by the thermal decomposition of uranium halides on a hot filament.
Uranium metal reacts with almost all nonmetallic elements and their compounds, with reactivity increasing with temperature. Hydrochloric and nitric acids dissolve uranium, but non-oxidizing acids other than hydrochloric acid attack the element very slowly. When finely divided, it can react with cold water. In air, uranium metal oxidizes and becomes coated with a dark layer of uranium oxide. Uranium forms a variety of alloys and compounds with the most important oxidation states being uranium(IV) and uranium(VI), and their two corresponding oxides are, respectively, uranium dioxide, UO2 and uranium trioxide, UO3. Besides the oxides, other Important uranium compounds include fluorides, chlorides, bromides, iodides, carbonates, hydrides, carbides, nitrides, phosphates, etc. At room temperatures, uranium hexafluoride, UF6, has a high vapor pressure, making it useful in the gaseous diffusion process used to separate the rare U-235 from the common U-238 isotope. Uranium hydrides, nitrides and carbides are relatively inertsemimetallic compounds that are minimally soluble in acids and have been used as stable fuel pellets in nuclear power reactor technology.
Uranium exists in aqueous solutions in the +3, +4, +5, and +6 oxidation states. Oxidation state +6 as the UO22+ ion (yellow in color) is the most stable state in solution. Uranium in the +5 state as the UO2+ ion is colorless, quite unstable and disproportionates (reacts with itself) to form the +6 and +4 states. The +4 state (green) is reasonably stable in solution, but the +3 state (dark green or dark red depending on the illumination source - daylight vs fluorescent light) is unstable and easily oxidizes to +4. The +4 state in near-neutral pH solutions readily hydrolyzes to form black oxy-hydroxide precipitates.
The name derives from the planet Uranus, which in Roman mythology was "Father Heaven". The German chemist Martin-Heinrich Klaproth discovered the element in 1789, following William Hershel's discovery of the planet in 1781. The metallic uranium was first isolated by the French chemist Eugène-Melchior Peligot in 1841.
Uranium was discovered by Martin Heinrich Klaproth, a German chemist, in the mineral pitchblende (primarily a mix of uranium oxides) in 1789. Although Klaproth, as well as the rest of the scientific community, believed that the substance he extracted from pitchblende was pure uranium, it was actually uranium dioxide (UO2). After noticing that 'pure' uranium reacted oddly with uranium tetrachloride (UCl4), Eugène-Melchoir Péligot, a French chemist isolated pure uranium by heating uranium dioxide with potassium in a platinum crucible. Radioactivity was first discovered in 1896 when Antoine Henri Becquerel, a French physicist, detected it from a sample of uranium. Today, uranium is obtained from uranium ores such as pitchblende, uraninite (UO2), carnotite (K2(UO2)2VO4·1-3H2O) and autunite (Ca(UO2)2(PO4)2·10H2O) as well as from phosphate rock (Ca3(PO4)2), lignite (brown coal) and monazite sand ((Ce, La, Th, Nd, Y)PO4). Since there is little demand for uranium metal, uranium is usually sold in the form of sodium diuranate (Na2U2O7·6H2O), also known as yellow cake, or triuranium octoxide (U3O8).
The use of uranium in its natural oxide form dates back to 79 A.D. when it was used as a yellow coloring agent in ceramic glazes. Yellow glass with 1% uranium oxide was found in an ancient Roman villa near Naples, Italy. In the late Middle Ages, pitchblende was extracted from the silver mines and was used as a coloring agent in the glassmaking industry. The identification of uranium as an element is generally credited to Martin H. Klaproth. While experimenting with pitchblende in 1789, he concluded that it contained a new element, which he named after the newly discovered planet Uranus (named after the Greek god of the sky or heaven). What Klaproth actually identified was not the pure element but uranium oxide. The pure metal was first isolated in 1841 by Eugène-Melchior Péligot, who reduced anhydrous uranium tetrachloride with potassium metal.
In 1896 Antoine H. Becquerel discovered that uranium exhibited invisible light or rays; it was radioactivity. In 1934 research by Enrico Fermi and others eventually led to the use of uranium fission in the first nuclear weapon used in war and later in the peaceful use of uranium as fuel in nuclear power production. An ensuing arms race during the Cold War between the United States and the Soviet Union produced tens of thousands of nuclear weapons that used uranium metal and uranium-derived plutonium-239. The security of those weapons and their fissile material following the breakup of the Soviet Union in 1991 is an ongoing concern.
In 1972 French physicist Francis Perrin discovered ancient and no longer active prehistoric natural nuclear fission reactors in uranium ore deposits at the Oklo mine in Gabon, West Africa, collectively known as the Oklo Fossil Reactors. The ore deposit is 1.7 billion years old; at that time, uranium-235 constituted about 3% of the total uranium on Earth (0.72% today). This is high enough to permit a sustained nuclear fission chain reaction to occur, provided other supporting geologic conditions exist.
Pure uranium is a silvery-gray metal when freshly prepared, but it darkens in air as oxide layers form. It is very dense, malleable in some forms, and exists in several solid allotropes below its melting point. Finely divided uranium can be pyrophoric.
The dominant use of uranium is as fuel for nuclear reactors after mining, conversion, isotopic enrichment when required, and fabrication into fuel, commonly uranium dioxide, UO₂. ²³⁵U is the principal naturally occurring fissile isotope used in most power reactors. Depleted uranium, left after enrichment, has been used in radiation shielding, counterweights, armor-piercing penetrators, and some military armor because of its high density. Uranium compounds were once used to color glass and ceramics, but such uses are now limited and regulated.
Since it is naturally radioactive, uranium, usually in the form of uranium dioxide (UO2), is most commonly used in the nuclear power industry to generate electricity. Naturally occurring uranium consists of three isotopes: uranium-234, uranium-235 and uranium-238. Although all three isotopes are radioactive, only uranium-235 is a fissionable material that can be used for nuclear power.
When a fissionable material is struck by a neutron, its nucleus can release energy by splitting into smaller fragments. If some of the fragments are other neutrons, they can strike other atoms and cause them to split as well. A fissionable material, such as uranium-235, is a material capable of producing enough free neutrons to sustain a nuclear chain reaction.
Only 0.7204% of naturally occurring uranium is uranium-235. This is too low a concentration to sustain a nuclear chain reaction without the help of a material known as a moderator. A moderator is a material that can slow down a neutron without absorbing it. Slow neutrons are more likely to react with uranium-235 and reactors using natural uranium can be made using graphite or heavy water as a moderator. Methods also exist for concentrating uranium-235. Once the levels of uranium-235 have been increased to about 3%, normal water can be used as a moderator.
Uranium-238, uranium's most common isotope, can be converted into plutonium-239, a fissionable material that can also be used as a fuel in nuclear reactors. To produce plutonium-239, atoms of uranium-238 are exposed to neutrons. Uranium-239 forms when uranium-238 absorbs a neutron. Uranium-239 has a half-life of about 23 minutes and decays into neptunium-239 through beta decay. Neptunium-239 has a half-life of about 2.4 days and decays into plutonium-239, also through beta decay.
Although it does not occur naturally, uranium-233 is also a fissionable material that can be used as a fuel in nuclear reactors. To produce uranium-233, atoms of thorium-232 are exposed to neutrons. Thorium-233 forms when thorium-232 absorbs a neutron. Thorium-233 has a half-life of about 22 minutes and decays into protactinium-233 through beta decay. Protactinium-233 has a half-life of about 27 days and decays into uranium-233, also through beta decay. If completely fissioned, one pound (0.45 kilograms) of uranium-233 will provide the same amount of energy as burning 1,500 tons (1,350,000 kilograms) of coal.
Uranium is a dense metal that has uses outside of the nuclear power industry. It is used as a target for X-ray production, as ammunition for some types of military weaponry, as a shield against radiation, as a counterweight for aircraft control surfaces and in the gyroscopes of inertial guidance systems.
Uranium compounds have been used for centuries to color glass. A 2,000 year old sample of yellow glass found near Naples, Italy contains uranium oxide. Uranium trioxide (UO3) is an orange powder and has been used in the manufacture of Fiestaware plates. Other uranium compounds have also been used to make vaseline glass and glazes. The uranium within these items is radioactive and should be treated with care.
Uranium's most stable isotope, uranium-238, has a half-life of about 4,468,000,000 years. It decays into thorium-234 through alpha decay or decays through spontaneous fission.
Uranium was used in as coloring agents in ceramic glazes and glass in ancient Rome and in the Middle Ages producing orange-red to lemon yellow hues. More recently it was used as an orange glaze in contemporary Fiestaware© dishware but was later discontinued for health reasons. Many contemporary uses of uranium exploit its unique nuclear properties. Uranium-235 has the distinction of being the only naturally occurring fissileisotope. This means it can be split into two or three fragments (fission products) by thermal neutrons. Uranium-238 is fissionable by fast neutrons, and is fertile, meaning it can be transmuted to fissile plutonium-239 in a nuclear reactor. Another fissile isotope, uranium-233, can be produced from natural thorium and is also important in nuclear technology. While uranium-238 has a small probability for spontaneous fission or even induced fission with fast neutrons, uranium-235 and to a lesser degree uranium-233 have a much higher fission cross-section for slow neutrons. In sufficient concentration, these isotopes maintain a sustained nuclear chain reaction. This generates the heat in nuclear power reactors, and produces the fissile material for nuclear weapons. This nuclear conversion can be brought about in breeder reactors where it is possible to produce more new fissionable material than the fissionable material used in maintaining the chain reaction. Depleted uranium (238U) (depleted of uranium-235) is used in balistic armor penetration and as armor plating.
Uranium-238 is not fissile, but is a fertile isotope, because after neutron activation it can produce plutonium-239, another fissile isotope. Indeed, the238U nucleus can absorb one neutron to produce the radioactive isotope uranium-239. 239U decays by beta emission to neptunium-239, also a beta-emitter, that decays in its turn, within a few days into plutonium-239. 239Pu was used as fissile material in the first atomic bomb detonated in the "Trinity test" on 15 July 1945 in New Mexico.
Uranium-235 is of even greater importance because it is the key to utilizing uranium. 235U, while occurring in natural uranium to the extent of only 0.71%, is so fissionable with slow neutrons that a self-sustaining fission chain reaction can be made in a reactor constructed from natural uranium and a suitable moderator, such as heavy water or graphite, alone.
Uranium-235 can be concentrated by gaseous diffusion and other physical processes, if desired, and used directly as a nuclear fuel, instead of natural uranium, or used as an explosive.
Natural uranium, slightly enriched with 235U by a small percentage, is used to fuel nuclear power reactors to generate electricity. Natural thorium can be irradiated with neutrons to produce the important isotope 233U as follows: 232Th(n, gamma) >233Th(beta) >233Pa(beta) >233U. While thorium itself is not fissionable, 233U is, and in this way may be used as a nuclear fuel. One pound of completely fissioned uranium has the fuel value of over 1500 tons of coal.
The uses of nuclear fuels to generate electrical power, to make isotopes for peaceful purposes, and to make explosives are well known. Uranium in the U.S.A. is controlled by the U.S. Nuclear Regulatory Commission. New uses are being found for depleted uranium, i.e., uranium with the percentage of 235U lowered to about 0.2%. Uranium is used in inertial guidance devices, in gyro compasses, as counterweights for aircraft control surfaces, as ballast for missile reentry vehicles, and as a shielding material. Uranium metal is used for X-ray targets for production of high-energy X-rays; the nitrate was once used as a photographic toner, and the acetate was once used in analytical chemistry. Crystals of uranium nitrate are triboluminescent. Uranium salts have also been used for producing yellow "Vaseline" glass and glazes.
Isotopes in Earth/Planetary Science
234U (with a half-life of 2.432×105 years) is a daughter product of 238U (with a half-life of 4.47×1010 years) and makes up only 0.0054 percent of the total uranium today. During the decay of the parent radionuclide 238U nucleus (first to 234Th (with a half-life of 24 days) by alpha decay, then to 234Pa (with a half-life of 6.7 h) by beta-minus, and finally to 234U by beta-minus), the energy released will damage the chemical and physical bonds holding the 234U product nuclei in a mineral. As a result, 234U may be leached more easily from water or rock samples than 238U and the isotope-amount ratio n(234U)/n(238U) will vary depending on the extent of water-rock interaction [598] J. Riotte, F. Chabaux. Geochim. Cosmochim. Acta63, 1263 (1999)..
Isotopes in Geochronology
The three natural radioactive decay chains beginning with 238U, 235U, and 232Th each have comparable half-lives that are much longer than the radioactive isotopes that follow until the production of stable isotopes of 206Pb, 207Pb, and 208Pb, respectively. When undisturbed, the activities of daughter isotopes in each decay chain are equal to their parents and one can measure the accumulation of the stable isotopes of lead to date the time that has elapsed since a mineral became a closed system (a system that does not exchange matter with its surroundings). Rocks formed hundreds of millions to billions of years ago can be dated using this technique [591] R. R. Parrish, S. R. Noble. Rev. Mineral. Geochem.53, 183 (2003).. If a mineral is disturbed at some point during the decay and isotopes in the decay chain are preferentially removed from the system, the equilibria in a decay sequence will be disturbed. For example, one can measure the excess of 230Th (with a half-life of 7.56×104 years) relative to the 234U parent radionuclide to date carbonates (speleothems or corals) that are less than 5×105 years old [591] R. R. Parrish, S. R. Noble. Rev. Mineral. Geochem.53, 183 (2003)..
Isotopes in Industry
Nuclei of 235U are split when bombarded by thermal neutrons. The process is known as nuclear fission and can release tremendous amounts of energy per uranium nucleus. The nucleus that splits will release additional neutrons that, if slowed down sufficiently, can cause subsequent fission events. When properly controlled, 235U fission can be used to generate heat to drive steam turbines, which in turn produces electricity (Fig. IUPAC.92.1). If the fission process is not controlled, then a rapid and explosive release of energy will occur, similar to that of nuclear weapons [599] M. G. Sowerby. 4.7.1 Nuclear Fission, Kaye & Laby-Tables of Physical & Chemical Constants. National Physical Laboratory (2014), Feb. 25; http://www.kayelaby.npl.co.uk/atomic_and_nuclear_physics/4_7/4_7_1.html.. Uranium depleted in 235U by fission in nuclear reactors (and hence greatly enriched in 238U compared to “natural” uranium) is used in the manufacture of DUCRETE concrete (Fig. IUPAC.92.2). The incorporation of the large 238U nuclei makes this material an effective absorber of neutrons and gamma rays, and DUCRETE concrete is used to reduce fluxes of neutrons and high-energy photons. The alpha particles produced by the decay of 238U are effectively absorbed by the concrete and do not pose a health risk. DUCRETE is being proposed as a suitable material for the storage of radioactive waste [600] C. M. Les Dole, J. Ferrada. Depleted Uranium as Aggregate in Concrete Shielding Material, Oak Ridge National Laboratory (2014), Feb. 25; http://web.ead.anl.gov/uranium/pdf/DUCRETEIntroductionJune2003.pdf., [601] Environmental Science Division, Argonne National Laboratory. High-Volume: Casks-DUCRETE, Environmental Science Division, Argonne National Laboratory (2014), Feb. 25; http://web.ead.anl.gov/uranium/uses/buscase/slide14.cfm..
Uranium forms compounds in several oxidation states, especially +4, +5, and +6, with +6 common in oxidizing aqueous environments as the linear uranyl ion, UO₂²⁺. Uranium dioxide, UO₂, is a major nuclear fuel material, while triuranium octoxide, U₃O₈, is a stable oxide often used for storage and assay. Uranium hexafluoride, UF₆, is volatile enough for isotope enrichment and is central to the nuclear fuel cycle. Uranyl nitrate, UO₂(NO₃)₂, and uranyl acetate, UO₂(CH₃COO)₂, are soluble laboratory and process compounds.
See more information at the Uranium compound page.
Uranium presents both chemical and radiological hazards. Natural and depleted uranium are weakly radioactive compared with many fission products, but inhaled dust or soluble compounds can deliver internal alpha radiation and cause heavy-metal toxicity, with the kidneys a principal chemical target. Enriched uranium has greater fissile content and requires criticality controls. Finely divided metal is a fire hazard, and uranium hexafluoride, UF₆, reacts with moisture to form corrosive hydrogen fluoride, HF.
Uranium occurs naturally in many rocks, soils, and waters at low concentrations, with higher levels in uranium-bearing minerals and some phosphates. Its mobility depends strongly on redox conditions and carbonate chemistry: oxidizing waters can transport soluble uranyl carbonate complexes, while reducing environments may immobilize U(IV) minerals. Mining, milling tailings, and fuel-cycle wastes can create localized contamination requiring long-term control of dust, drainage, and radon-bearing decay products.
Uranium is mined mainly from uranium ores or recovered by in situ leaching where geology permits. Concentrates are processed through conversion and, for many reactor designs, enrichment before fuel fabrication. Demand is driven chiefly by nuclear electricity generation, with strategic inventories and long contracting cycles making the market different from ordinary industrial metals. Recycling is possible through reprocessing spent fuel, but its use depends on reactor type, policy, safeguards, and economics. Depleted uranium is abundant as an enrichment by-product and has limited specialized markets.
Uranium is the heaviest naturally-occurring element available in large quantities. The heavier “transuranic” elements are either man-made or they exist only as trace quantities in uranium ore deposits as activation products. Uranium occurs naturally in low concentrations of a few parts per million in soil, rock and water, and is commercially extracted from uranium-bearing minerals. Uranium, not as rare as once thought, is now considered to be more plentiful than mercury, antimony, silver, or cadmium, and is about as abundant as molybdenum or arsenic. It occurs in numerous natural minerals such as pitchblende, uraninite, carnotite, autunite, uranophane, and tobernite. It is also found in phosphate rocks, lignite, monazite sands, and is recovered commercially from these sources. The United States Department of Energy purchases uranium in the form of acceptable U3O8 concentrates. This incentive program has greatly increased the known uranium reserves.
Uranium is produced in rare, neutron-rich nucleosynthesis events, most likely including neutron-star mergers and some classes of supernova-related environments. It is present only in trace cosmic abundance because it is heavy and radioactive. Long-lived ²³⁸U and ²³⁵U were incorporated into the early Solar System and remain useful in planetary heat production and radiometric dating, although ²³⁵U has decayed much more substantially over geologic time.
- Natural uranium contains only about 0.7% ²³⁵U by atoms.
- Fresh uranium metal tarnishes rapidly even when the bulk metal remains solid and massive.
- Uranium glass can fluoresce green under ultraviolet light.
- Uranium hexafluoride is used for enrichment because it can be made into a gas at moderate temperatures.
- The isotope ²³⁸U can breed plutonium-239 in reactors after neutron capture.
- Ancient natural nuclear fission reactors operated at Oklo in Gabon about two billion years ago.
Immagini
Proprietà
Fisiche
- Raggio atomico (empirico)
- 175 pm Confronta Raggio atomico (empirico) di tutti gli elementi →
- Raggio covalente
- 196 pm Confronta Raggio covalente di tutti gli elementi →
- Raggio di van der Waals
- 240 pm Confronta Raggio di van der Waals di tutti gli elementi →
- Densità
- 1,895 × 104 kg/m³ Confronta Densità di tutti gli elementi →
- Volume molare
- 0,0125 L/mol
- Fase in condizioni STP
- Solido Confronta Fase in condizioni STP di tutti gli elementi →
- Punto di fusione
- 1134,85 °C Confronta Punto di fusione di tutti gli elementi →
- Punto di ebollizione
- 4130,85 °C Confronta Punto di ebollizione di tutti gli elementi →
- Conducibilità termica
- 27,5 W/(m·K) Confronta Conducibilità termica di tutti gli elementi →
- Capacità termica specifica
- 0,116 J/(g·K) Confronta Capacità termica specifica di tutti gli elementi →
- Capacità termica molare
- 27,665 J/(mol·K) Confronta Capacità termica molare di tutti gli elementi →
- Struttura cristallina
- Ortorombica Confronta Struttura cristallina di tutti gli elementi →
Chimiche
- Elettronegatività (Pauling)
- 1,38 Confronta Elettronegatività (Pauling) di tutti gli elementi →
- Affinità elettronica
- 0,3 eV
- Energia di ionizzazione (1ª)
- 6,19405 eV Confronta Energia di ionizzazione (1ª) di tutti gli elementi →
- Energia di ionizzazione (2ª)
- 11,60004 eV Confronta Energia di ionizzazione (2ª) di tutti gli elementi →
- Energia di ionizzazione (3ª)
- 19,800068 eV Confronta Energia di ionizzazione (3ª) di tutti gli elementi →
- Energia di ionizzazione (4ª)
- 36,700126 eV Confronta Energia di ionizzazione (4ª) di tutti gli elementi →
- Energia di ionizzazione (5ª)
- 46,000158 eV Confronta Energia di ionizzazione (5ª) di tutti gli elementi →
- Stati di ossidazione
- −1, +1, +2, +3, +4, +5, +6 Confronta Stati di ossidazione di tutti gli elementi →
- Elettroni di valenza
- 3 Confronta Elettroni di valenza di tutti gli elementi →
- Configurazione elettronica
- [Rn] 7s2 5f3 6d1
Termodinamiche
- Calore di fusione
- 0,14561849 eV Confronta Calore di fusione di tutti gli elementi →
- Calore di vaporizzazione
- 4,321915 eV Confronta Calore di vaporizzazione di tutti gli elementi →
- Calore di sublimazione
- 5,524175 eV
- Calore di atomizzazione
- 5,524175 eV
- Entalpia di atomizzazione
- 5,524175 eV
Nucleari
- Protoni
- 92 Confronta Protoni di tutti gli elementi →
- Neutroni
- 146 Confronta Neutroni di tutti gli elementi →
- Isotopi noti
- 29 Confronta Isotopi noti di tutti gli elementi →
- Isotopi stabili
- 0 Confronta Isotopi stabili di tutti gli elementi →
- Isotopo più stabile
- U-238
- Anno della scoperta
- 1789
Abbondanza
- Abbondanza (crosta terrestre)
- 2,7 mg/kg Confronta Abbondanza (crosta terrestre) di tutti gli elementi →
- Abbondanza (oceano)
- 0,003 mg/L Confronta Abbondanza (oceano) di tutti gli elementi →
Struttura cristallina
- Costante reticolare a
- 285 pm
Struttura elettronica
- Elettroni per guscio
- 2, 8, 18, 32, 21, 9, 2 Confronta Elettroni per guscio di tutti gli elementi →
Identificativi
- Numero CAS
- 7440-61-1 Confronta Numero CAS di tutti gli elementi →
- Simbolo di termine
- 5L°6
- InChI
- InChI=1S/U
- Chiave InChI
- JFALSRSLKYAFGM-UHFFFAOYSA-N
Configurazione elettronica Misurato
U: 5f³ 6d¹ 7s²[Rn] 5f³ 6d¹ 7s²1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f¹⁴ 5d¹⁰ 6s² 6p⁶ 5f³ 6d¹ 7s²Modello atomico
Gli isotopi modificano il numero di neutroni, la massa e la stabilità — non la configurazione elettronica di un atomo neutro.
Modello atomico schematico, non in scala.
Impronta atomica
Spettro di emissione / assorbimento
Distribuzione isotopica
Nessun isotopo stabile.
| Numero di massa | Massa atomica (u) | Abbondanza naturale | Emivita |
|---|---|---|---|
| 217 Radioattivo | 217,02466 ± 0,00011 | N/D | 850 us |
| 235 Radioattivo | 235,0439301 ± 0,0000019 | 0,7204% | 704 My |
| 221 Radioattivo | 221,02628 ± 0,00011 | N/D | 660 ns |
| 224 Radioattivo | 224,027605 ± 0,000027 | N/D | 396 us |
| 218 Radioattivo | 218,023523 ± 0,00002 | N/D | 354 us |
Fase / Stato
Motivo: 1109,8 °C sotto il punto di fusione (1134,85 °C)
Schema non in scala
Punti di transizione di fase
Energie di transizione
Energia necessaria per fondere 1 mol al punto di fusione
Energia necessaria per vaporizzare 1 mol al punto di ebollizione
Energia necessaria per sublimare 1 mol al punto di sublimazione
Densità
In condizioni standard
In condizioni standard
Spettri atomici
Sono visualizzati 10 di 92. Ordinamento per carica ionica crescente.
Righe disponibili ?
| Ione | Carica | Righe totali | Probabilità di transizione | Designazioni dei livelli |
|---|---|---|---|---|
| U I | 0 | 216 | 57 | 0 |
| U II | +1 | 258 | 0 | 0 |
Livelli disponibili ?
| Ione | Carica | Livelli |
|---|---|---|
| U I | 0 | 2 |
| U II | +1 | 2 |
| U III | +2 | 2 |
| U IV | +3 | 2 |
| U V | +4 | 2 |
| U VI | +5 | 2 |
| U VII | +6 | 2 |
| U VIII | +7 | 2 |
| U IX | +8 | 2 |
| U X | +9 | 2 |
Raggi ionici
Sono visualizzati 10 di 14.
| Carica | Coordinazione | Spin | Raggio |
|---|---|---|---|
| +3 | 6 | N/D | 102.49999999999999 pm |
| +3 | 9 | N/D | 118.9 pm |
| +4 | 6 | N/D | 89 pm |
| +4 | 7 | N/D | 95 pm |
| +4 | 8 | N/D | 100 pm |
| +4 | 9 | N/D | 105 pm |
| +4 | 12 | N/D | 117 pm |
| +5 | 6 | N/D | 76 pm |
| +5 | 7 | N/D | 84 pm |
| +6 | 2 | N/D | 45 pm |
Composti
Isotopi (5)
Uranium is weakly radioactive because all naturally occurring (or primordial) isotopes of uranium (238U, 235U and 234U) are unstable, with half-lives varying between 159,200 years and 4.5 billion years. There are 27 known isotopes of uranium ranging in atomic weights 217–219, 222–240 and 242, with half-lives of from billions of years to a few nanoseconds. Naturally occurring uranium consists of three major isotopes: 238U (99.28% abundance), 235U (0.71%), and 234U (0.0054%). (The US DOE has adopted the value of 0.711 as being their official percentage of 235U in natural uranium.) All three isotopes are radioactive, with small probabilities of undergoing spontaneous fission but preferentially decaying by alpha emission. The half-life of uranium-238 is about 4.47 billion years and that of uranium-235 is 704 million years, making them useful in dating the age of the Earth. It also suggests that half of the uranium that existed from the formation of the Earth has decayed to other radioactive elements and eventually to stable elements. Much of the internal heat of the earth is thought to be attributable to the decay of uranium and thorium radio-isotopes.
| Numero di massa | Massa atomica (u) | Abbondanza naturale | Emivita | Modalità di decadimento | |
|---|---|---|---|---|---|
| 217 Radioattivo | 217,02466 ± 0,00011 | N/D | 850 us | α ≈100%β- ? | |
| 235 Radioattivo | 235,0439301 ± 0,0000019 | 0,7204% ± 0,0006% | 704 My | IS =0.7204±0.6%α =100%SF =7e-9±0.2% | |
| 221 Radioattivo | 221,02628 ± 0,00011 | N/D | 660 ns | α ≈100%β+ ? | |
| 224 Radioattivo | 224,027605 ± 0,000027 | N/D | 396 us | α =100%β+ ? | |
| 218 Radioattivo | 218,023523 ± 0,00002 | N/D | 354 us | α =100% |
Proprietà estese
Raggi covalenti (dati estesi)
- Raggio covalente (Pyykkö)
- 170 pm
- Raggio covalente (Pyykkö, legame doppio)
- 134 pm
- Raggio covalente (Pyykkö, legame triplo)
- 118 pm
Raggi di van der Waals
- Batsanov
- 230 pm
- Alvarez
- 271 pm
- UFF
- 339,5 pm
- MM3
- 252 pm
Raggi atomici e metallici
- Raggio atomico (Rahm)
- 283 pm
Scale di numerazione
- Mendeleev
- 20
- Pettifor
- 45
- Glawe
- 36
Scale di elettronegatività
- Ghosh
- 0
- Miedema
- 4
Polarizzabilità e dispersione
- Polarizzabilità dipolare
- 129 a.u.
- Polarizzabilità dipolare (inc.)
- 17 a.u.
Affinità chimica
- Affinità protonica
- 995,2 kJ/mol
- Basicità in fase gassosa
- 973,2 kJ/mol
Parametri di Miedema
- Volume molare di Miedema
- 13,15 cm3/mol
- Densità elettronica di Miedema
- 3
Rischio di approvvigionamento ed economia
- Concentrazione della produzione
- 33
- Rischio relativo di approvvigionamento
- 6
- Distribuzione delle riserve
- 31
- Stabilità politica (principale produttore)
- 62
- Stabilità politica (principale detentore di riserve)
- 75
Transizioni di fase e allotropi
| Punto di fusione | 1408,15 K |
| Punto di ebollizione | 4404,15 K |
Categorie degli stati di ossidazione
Dati di riferimento avanzati
Dettaglio dei raggi cristallini (14)
| Carica | CN | Spin | rcrystal (pm) | Origine |
|---|---|---|---|---|
| 3 | VI | 116,5 | from r^3 vs V plots, | |
| 4 | VI | 103 | ||
| 4 | VII | 109 | estimated, | |
| 4 | VIII | 114 | from r^3 vs V plots, | |
| 4 | IX | 119 | ||
| 4 | XII | 131 | estimated, | |
| 5 | VI | 90 | ||
| 5 | VII | 98 | estimated, | |
| 6 | II | 59 | ||
| 6 | IV | 66 |
Modalità di decadimento degli isotopi (60)
| Isotopo | Modalità | Intensità |
|---|---|---|
| 215 | A | — |
| 215 | B+ | — |
| 216 | A | 100% |
| 217 | A | 100% |
| 217 | B- | — |
| 218 | A | 100% |
| 219 | A | 100% |
| 219 | B+ | — |
| 220 | A | — |
| 220 | B+ | — |
Fattori di diffusione dei raggi X (514)
| Energia (eV) | f₁ | f₂ |
|---|---|---|
| 10 | — | 1,627 |
| 10,1617 | — | 1,61282 |
| 10,3261 | — | 1,59877 |
| 10,4931 | — | 1,58416 |
| 10,6628 | — | 1,56547 |
| 10,8353 | — | 1,547 |
| 11,0106 | — | 1,52874 |
| 11,1886 | — | 1,5107 |
| 11,3696 | — | 1,49287 |
| 11,5535 | — | 1,47526 |
Dati aggiuntivi
Estimated Crustal Abundance
The estimated element abundance in the earth's crust.
2.7 milligrams per kilogram
Riferimenti (1)
Estimated Oceanic Abundance
The estimated element abundance in the earth's oceans.
3.2×10-3 milligrams per liter
Riferimenti (1)
Sources
Sources of this element.
Uranium is the heaviest naturally-occurring element available in large quantities. The heavier “transuranic” elements are either man-made or they exist only as trace quantities in uranium ore deposits as activation products. Uranium occurs naturally in low concentrations of a few parts per million in soil, rock and water, and is commercially extracted from uranium-bearing minerals. Uranium, not as rare as once thought, is now considered to be more plentiful than mercury, antimony, silver, or cadmium, and is about as abundant as molybdenum or arsenic. It occurs in numerous natural minerals such as pitchblende, uraninite, carnotite, autunite, uranophane, and tobernite. It is also found in phosphate rocks, lignite, monazite sands, and is recovered commercially from these sources. The United States Department of Energy purchases uranium in the form of acceptable U3O8 concentrates. This incentive program has greatly increased the known uranium reserves.
Riferimenti (1)
- [6] Uranium https://periodic.lanl.gov/92.shtml
Riferimenti
(9)
Data deposited in or computed by PubChem
The half-life and atomic mass data was provided by the Atomic Mass Data Center at the International Atomic Energy Agency.
Element data are cited from the Atomic weights of the elements (an IUPAC Technical Report). The IUPAC periodic table of elements can be found at https://iupac.org/what-we-do/periodic-table-of-elements/. Additional information can be found within IUPAC publication doi:10.1515/pac-2015-0703 Copyright © 2020 International Union of Pure and Applied Chemistry.
The information are cited from Pure Appl. Chem. 2018; 90(12): 1833-2092, https://doi.org/10.1515/pac-2015-0703.
Thomas Jefferson National Accelerator Facility (Jefferson Lab) is one of 17 national laboratories funded by the U.S. Department of Energy. The lab's primary mission is to conduct basic research of the atom's nucleus using the lab's unique particle accelerator, known as the Continuous Electron Beam Accelerator Facility (CEBAF). For more information visit https://www.jlab.org/
The periodic table at the LANL (Los Alamos National Laboratory) contains basic element information together with the history, source, properties, use, handling and more. The provenance data may be found from the link under the source name.
The periodic table contains NIST's critically-evaluated data on atomic properties of the elements. The provenance data that include data for atomic spectroscopy, X-ray and gamma ray, radiation dosimetry, nuclear physics, and condensed matter physics may be found from the link under the source name. Ref: https://www.nist.gov/pml/atomic-spectra-database
This section provides all form of data related to element Uranium.
The element property data was retrieved from publications.