Uranium (U)


Uranium is a chemical element with the atomic number 92 in the periodic table. This substance makes up about two parts per million of Earth’s crust. Uranium in the layers of Earth is as common as the elements tin, tungsten, and molybdenum.

As a member of the actinide series of periodic table elements, this naturally occurring radioactive element has been used as an abundant source of nuclear energy and in the making of atomic bombs for over 60 years. Uranium is also applied in nanotechnology, virology, cancer research, radiometric dating, materials science, etc. 

Fact Box

Chemical and Physical Properties of Uranium

The symbol in the periodic table of elements: U

Atomic number: 92

Atomic weight (mass): 238.03 g.mol-1

Group number: Actinides

Period: 7 (f-block)

Color: A sivery-white metallic element 

Physical state: Solid at room temperature

Half-life: From 0.52(+0.95−0.21) milliseconds to 4.4683×109 years 

Electronegativity according to Pauling: 1.7

Density: 18.95 g.cm-3 at 20°C

Melting point: 1135°C, 2075°F, 1408 K

Boiling point: 4131°C, 7468°F, 4404 K

Van der Waals radius: 0.121 nm

Ionic radius: 0.103 nm (+3); 0.093 nm (+4)

Isotopes: 29

Most characteristic isotope: 234U, 235U, 238U

Electronic shell: [Rn] 5f3 6d1 7s2

The energy of the first ionization: 6.1941 eV.

The energy of the second ionization: N/A

Discovery date: In 1789 by Martin Klaproth

With the periodic table symbol U, atomic number 92, atomic mass of 238.03 g.mol-1, and electron configuration X, uranium is a dense, hard, ductile, and malleable sivery-white radioactive element. This metallic substance reaches its boiling point at 4131°C, 7468°F, 4404 K, while the melting point is achieved at 1135°C, 2075°F, 1408 K. 

A uranium atom has 92 protons and 92 electrons. Six of them are valence electrons. Uranium is a member of the actinides group in the periodic table with an electronegativity of 1.7 according to Pauling, whereas the atomic radius according to van der Waals is 0.121 nm. Also, this chemical is an electropositive element with an orthorhombic structure. When exposed to air, it quickly tarnishes.                          

How Was Uranium Discovered?

Martin Heinrich Klaproth (1743 – 1817) was a German apothecary and chemist. Interested in the structure of minerals, in 1789 his scientific curiosity was triggered by a sample of the mineral pitchblende (uranium dioxide or uranium(IV) oxide (UO2). Convinced that he had a zinc/iron ore in his hands, Klaproth attempted to dissolve the pitchblende in nitric acid. In the next step, he added potash (an alkaline potassium compound) to the substance in an effort to produce yellow precipitation. 

However, the result was not anticipated or familiar to Klaproth. Because the potash dissolved the yellow precipitate, the German chemist concluded that the substance in front of him is, in fact, a new chemical element.

In 1841, the French chemist Eugène-Melchior Péligot (1811-1890) succeeded in isolating the first sample of uranium metal by conducting a reduction of uranium tetrachloride (UCl4) with potassium. 

The Discovery of Radiation 

Studying phosphorescence and x-ray properties, the French physicist Henri Becquerel had serendipitously discovered the phenomenon of radiation in 1896. Namely, by exposing uranium-based crystals wrapped in thick black paper to sunlight, he observed a shadow on the photographic plate where the crystals were positioned that had pierced through the paper. 

The discovery of this French scientist further led the way of Marie and Pierre Curie to the discovery of the radioactive elements polonium and radium. The Curies were also the first scientists who had coined and used the term radioactivity

How Did Uranium Get Its Name?

Since Martin Klaproth discovered uranium by an unexpected chemical reaction, he named the new element ‘uranium’ after the newly found planet Uranus. In astronomy, the seventh planet from the Sun was named Uranus after the Greek God of the Sky, and represents sudden and unpredictable changes. 

Where Can You Find Uranium?

About 6.6 billion years ago, uranium was created in the Universe by supernova explosions. With an abundance of over 4 parts per million in Earth’s crust, uranium naturally occurs in many minerals. Low concentrations of uranium can be traced in water, soil, rocks, and air. 

Nowadays, element 92 is primarily obtained from the minerals pitchblende, uranitide, torbernite, autunite, torbernite, and carnotite. It’s mainly isolated by an ion-exchange technique, in heap leach facilities, in situ recovery facilities, as well as in uranium mills. 

Kazakhstan, Canada, Australia, Niger, Namibia, Russia, USA, Uzbekistan, United States, China, South Africa and Germany are among the world’s largest producers of uranium. 

List of Uranium Minerals

The wast list of minerals in which uranium occurs contains the following items:


  • Albrechtschraufite
  • Althupite
  • Agrinierite
  • Andersonite
  • Arsenuranospathite
  • Betafite
  • Bayleyite
  • Becquerelite
  • Belakovskiite
  • Bergenite
  • Bijvoetite-(Y)
  • Billietite
  • Boltwoodite
  • Braunerite
  • Clarkeite
  • Carnotite
  • Coconinoite
  • Cuprosklodowskite
  • Curite
  • Davidite
  • Demesmaekerite
  • Derriksite
  • Euxenite
  • Gummite
  • Mathesiusite
  • Metatorbernite
  • Mckelveyite-(Y)
  • Meyrowitzite
  • Margaritasite
  • Marthozite
  • Masuyite
  • Meisserite
  • Metazeunerite
  • Mundite
  • Polycrase
  • Rameauite
  • Rutherfordine
  • Steacyite
  • Sklodowskite
  • Soddyite
  • Studtite
  • Thorianite
  • Umohoite
  • Uranocircite
  • Uranophane
  • Uranopilite
  • Wyartite
  • Yttrogummite

Uranium in Everyday Life

This radioactive chemical element has a reputation of being an element of choice for the creation of deadly weapons. However, element 92 has both military and civilian uses.

  • All uranium ores are sources of nuclear fuel. Namely, they release more energy than all deposits of fossil fuels found in Earth’s layers.
  • Small quantities of uranium are used in the manufacturing process of photographic chemicals, light bulbs, and ceramic glazes. Also, it’s applied in the production of compasses and missile vehicles.
  • The high density of this actinide is utilized in the keels of yachts, and as counterweights for aircraft control surfaces.
  • Uranium dioxide is commonly used in nuclear reactors for production of nuclear energy.
  • Since all uranium isotopes are radioactive, they are employed in the geological radioactive dating. Uranium–lead dating, or U–Pb dating, is one of the oldest radiometric methods for dating of rocks that originate from over 4.5 billion years ago.
  • Most commercial reactor fuel uses low enriched uranium (LEU). On the other hand, the nuclear reactors that use natural uranium as their fuel often employ heavy water as a moderator and coolant. The pressurized heavy water nuclear reactors do not require enriched uranium, which makes the process more ecological.
  • Both plutonium and uranium are used in the production of nuclear weapons, due to their ability to sustain a nuclear chain reaction which results in greater explosive power.

How Dangerous Is Uranium?

The prolonged exposure to radioactive uranium uranium and its decay products (especially radon) via contaminated air, water, soil, food, or direct contact with this substance, is extremely dangerous. Uranium’s toxicity and internal radiation caused by its radionuclides may lead to severe damage of all bodily organs and tissues, as well as to development of cancer of bones, bloodstream, kidneys, and lungs.

It should be noted that uranium is not absorbed through the skin. Also, the alpha particles released by this radioactive element cannot penetrate the skin.

Depleted Uranium

Obtained as a by-product of the enrichment process of natural uranium for nuclear fuel, depleted uranium is a dense radioactive metal mainly used for adding bigger penetrating power to the armor-piercing projectiles and weapons. Since it carries even more radioactivity than the naturally occurring uranium, depleted uranium represents a severe radiological health hazard that often results in lethal health effects and conditions. 

Environmental Effects of Uranium

Uranium is released in the environment via industrial or mining processes, improperly treated nuclear waste and radioactive materials from the nuclear power plants, or after a nuclear catastrophe (such as the Chernobyl nuclear power plant disaster). Uranium mining and provision of nuclear energy is one of the biggest environmental threats and highest environmental impact. According to the World Nuclear Association (WAD), this is due to the ineffective or nonexistent environmental or health and safety rules of the countries engaged in uranium mining and production. 

Isotopes of Uranium

Naturally occurring uranium has no stable isotopes. The naturally occurring form of element 92 is made up of three radioisotopes: 

  • Uranium-238 isotope (99.27 percent of abundance, with a half-life of 4,510,000,000-years); 
  • Uranium-235 isotope (0.72 percent of abundance, with a half-life of 713,000,000-years); 
  • Uranium-234 isotope (0.006 percent of abundance, with a half-life of 247,000-years).

The most important form of element 92 is the isotope U-235 because it can be readily split under specific conditions by creating a self-sustaining cascade of nuclear fission. In this way, it releases a massive amount of energy. 

Uranium’s decay chain (also labeled as “actinium series” or “actinium cascade”) produces 14 different chemical elements. In addition, it has been postulated that uranium-232 can be produced by a beta decay of thorium-232. 

The most abundant and the most stable longest isotope of uranium (238U) has a half-life of 4.4683×109 years which also nears the age of our planet Earth. 


[n 1]



Z N Isotopic mass (Da)[4]

[n 2][n 3]

Half-life Decay


[n 4]



[n 5][n 6]

Spin and


[n 7][n 8]

Natural abundance (mole fraction)
Excitation energy[n 8] Normal proportion Range of variation
214U[5] 92 122 0.52(+0.95−0.21) ms α 210Th 0+
215U[6] 92 123 215.026760(90) 2.24 ms α 211Th 5/2−#
216U[6][7] 92 124 216.024760(30) 2.25(+0.63−0.40) ms[5] α 212Th 0+
217U 92 125 217.02437(9) 26(14) ms

[16(+21−6) ms]

α 213Th 1/2−#
218U 92 126 218.02354(3) 0.65(+0.08−0.07) ms[5] α 214Th 0+
219U 92 127 219.02492(6) 55(25) μs

[42(+34−13) μs]

α 215Th 9/2+#
221U[9] 92 129 221.02640(11)# 0.66(14) μs α 217Th (9/2+)
222U 92 130 222.02609(11)# 1.4(7) μs

[1.0(+10−4) μs]

α 218Th 0+
β+ (10−6%) 222Pa
223U 92 131 223.02774(8) 21(8) μs

[18(+10−5) μs]

α 219Th 7/2+#
224U 92 132 224.027605(27) 940(270) μs α 220Th 0+
225U 92 133 225.02939# 61(4) ms α 221Th (5/2+)#
226U 92 134 226.029339(14) 269(6) ms α 222Th 0+
227U 92 135 227.031156(18) 1.1(1) min α 223Th (3/2+)
β+ (.001%) 227Pa
228U 92 136 228.031374(16) 9.1(2) min α (95%) 224Th 0+
EC (5%) 228Pa
229U 92 137 229.033506(6) 58(3) min β+ (80%) 229Pa (3/2+)
α (20%) 225Th
230U 92 138 230.033940(5) 20.8 d α 226Th 0+
SF (1.4×10−10%) (various)
β+β+ (rare) 230Th
231U 92 139 231.036294(3) 4.2(1) d EC 231Pa (5/2)(+#)
α (.004%) 227Th
232U 92 140 232.0371562(24) 68.9(4) y α 228Th 0+
CD (8.9×10−10%) 208Pb


CD (5×10−12%) 204Hg


SF (10−12%) (various)
233U 92 141 233.0396352(29) 1.592(2)×105 y α 229Th 5/2+ Trace[n 9]
SF (6×10−9%) (various)
CD (7.2×10−11%) 209Pb


CD (1.3×10−13%) 205Hg


234U[n 10][n 11] Uranium II 92 142 234.0409521(20) 2.455(6)×105 y α 230Th 0+ [0.000054(5)][n 12] 0.000050–


SF (1.73×10−9%) (various)
CD (1.4×10−11%) 206Hg


CD (9×10−12%) 184Hf



235U[n 13][n 14][n 15] Actin Uranium


92 143 235.0439299(20) 7.038(1)×108 y α 231Th 7/2− [0.007204(6)] 0.007198–


SF (7×10−9%) (various)
CD (8×10−10%) 186Hf



235mU 0.0765(4) keV ~26 min IT 235U 1/2+
236U Thoruranium[10] 92 144 236.045568(2) 2.342(3)×107 y α 232Th 0+ Trace[n 16]
SF (9.6×10−8%) (various)
237U 92 145 237.0487302(20) 6.75(1) d β 237Np 1/2+ Trace[n 17]
238U[n 11][n 13][n 14] Uranium I 92 146 238.0507882(20) 4.468(3)×109 y α 234Th 0+ [0.992742(10)] 0.992739–


SF (5.45×10−5%) (various)
ββ (2.19×10−10%) 238Pu
239U 92 147 239.0542933(21) 23.45(2) min β 239Np 5/2+
240U 92 148 240.056592(6) 14.1(1) h β 240Np 0+ Trace[n 18]
α (10−10%) 236Th
242U 92 150 242.06293(22)# 16.8(5) min β 242Np 0+

Source: Wikipedia

List of Uranium Compounds 

This electropositive chemical element may adopt the oxidation states +1, +2, +3, +4, +5, and +6. When compounded with other metals, uranium metal is able to form other intermetallic compounds, as well as solutions and solids. Most often element 92 participates in oxides and carbonates, of which some can be soluble. 

The following is a list of the most commonly prepared uranium compounds:


  • Yellowcake
  • Uranium hexafluoride
  • Cerium uranium blue
  • Diuranium pentoxide
  • Ferrouranium
  • MOX fuel
  • Pentavalent uranyl complexes
  • Tetrauranium octadecafluoride
  • Uranium diboride
  • Uranium carbide
  • Template:Uranium compounds
  • Uranium disilicide
  • Uranium hexoxide
  • Uranium monosulfide
  • Triuranium octoxide
  • Uranium oxide
  • Uranium pentabromide
  • Uranium pentachloride
  • Uranium pentafluoride
  • Uranium pentaiodide
  • Uranium rhodium germanium
  • Uranium ruthenium silicide
  • Uranous

5 Interesting Facts and Explanations

  1. Pitchblende is a form of the mineral uraninite (a radioactive uranium-rich ore) that occurs in black or brown formations. This high mineral substance may also contain traces of lead, thorium, and rare-earth elements oxides. 
  2. Uranium oxides that are formed during the purification of uranium ores are referred to as yellowcake
  3. Uranium has the second-highest atomic weight of all naturally occurring elements.
  4. All members of the actinide series of the periodic table are radioactive. This is a result of their large nuclei with unstable electron configuration that is able to release enormous energy. Most of these chemical elements are synthetically produced.
  5. Until the discovery of neptunium in 1940, Mendeleev’s predicted periodic system of elements had a dedicated position for uranium as the heaviest chemical element to be classified in the table.